HUMAN 


PHYSIOLOGY 


PREPARED  WITH  SPECIAL  REFERENCE  TO 


STUDENTS  OF  MEDICINE 


BY 

JOSEPH  HOWARD  RAYMOND,  A.M.,  M.D. 

V  IN 

Professor  of  Physiology  and  Hygiene  in  the  Long  Island  College  Hospital,  New  York  City 


THIRD  EDITION,  THOROUGHLY  REVISED 

444  Illustrations,  some  of  them  in  Colors,  and  4  full-page 
Lithographic  Plates 


PHILADELPHIA  AND  LONDON 

.  B.  SAUNDERS  &  COMPANY 
J905 


rs 


3IOLOGY 

LIBRARY 

8 


Set  up,  electrotyped,  printed,  and  copyrighted  September,  1894.     Reprinted  March,  1895. 

Revised,  entirely  reset,  reprinted,  and  recopyrighted  September,  1901. 

Revised,  reprinted,  and  recopyrighted  April,  1905. 


Copyright,  1905,  by  W.  B.  Saunders  &  Company. 


7 


PRESS  OF 
W.   B.    SAUNDERS  &  COMPANY, 


TO   THE  MEMORY 


ALEXANDER  JOHNSTON  CHALMERS  SKENE,  M.D.,  LL.D. 

COLLEAGUE  AND  FRIEND  FOR  MORE  THAN  A 
QUARTER  OF  A  CENTURY 

This  Volume  is  Affectionately  Inscribed  by 
THE  AUTHOR 


PREFACE  TO  THE  THIRD  EDITION. 


IN  the  present  edition  the  author  has  availed  himself  of  the 
valuable  contribution  of  Chittenden,  under  the  title  of  "  Physi- 
ological Economy  of  Nutrition,"  to  this  portion  of  Human 
Physiology.  The  results  of  the  experiments  therein  reported 
he  regards  as  among  the  most  important  additions  to  the  physi- 
ology of  nutrition  made  during  the  present  decade. 

The  completion  of  the  work  of  Atwater  and  others,  as  recorded 
in  the  publication  entitled  "  Physiological  Aspects  of  the  Liquor 
Problem/7  has  enabled  the  author  to  discuss  more  fully  the  nutritive 
value  of  alcohol. 

Among  other  topics,  either  more  fully  elaborated  or  introduced 
for  the  first  time,  are :  Vegetarianism ;  The  Identity  of  Human 
and  Bovine  Tuberculosis  in  connection  with  the  subject  of  Food ; 
The  Experiments  of  Cannon  and  others  on  the  Movements  of 
the  Stomach  and  Intestines ;  The  Influence  of  Alcohol  and  Alco- 
holic Fluids  on  the  Excretion  of  Uric  Acid ;  Hemolysis  and 
Bacteriolysis ;  The  Effect  of  Cold  on  Bacteria  with  reference 
to  the  purification  of  water  in  freezing ;  and  Ovarian  and  Ab- 
dominal Pregnancy. 

Many  other  minor  changes  have  been  made  in  the  text, 
rendered  necessary  by  the  advance  in  Physiology  since  the  publi- 
cation of  the  previous  edition. 

The  author  desires  to  extend  his  thanks  to  critics  who  have 
pointed  out  defects  in  the  former  edition,  which  might  otherwise 
have  escaped  detection,  and  all  of  which  he  hopes  have  been  cor- 
rected in  the  present  edition. 

APRIL  15,  1905. 

9 


PREFACE. 


THE  author's  experience  of  twenty  years  as  a  teacher  of 
Physiology  to  medical  students  has  brought  him  to  the  con- 
clusion that  in  the  short  time  allotted  to  the  study  of  physi- 
ology in  medical  schools  students  can  assimilate  only  the  main 
facts  and  principles  of  this  branch  of  medicine,  which  lies  at 
the  very  foundation  of  a  sound  knowledge  of  the  healing  art; 
and  that  even  if  there  were  time  to  investigate  the  more 
recondite  and  abstruse  parts  of  the  subject,  such  an  investiga- 
tion would  be  profitless  during  this  formative  period.  In  his 
teaching  the  author  has  kept  this  thought  constantly  in  mind, 
and  in  this  manual  has  endeavored  to  put  into  a  concrete  and 
available  form  the  results  of  his  experience. 

11 


CONTENTS. 


PAGE 

INTRODUCTION 17 

Definitions,  17 — Branches  of  Physiology,  19— Human  Physiology 
Defined,  20 — Classification  of  Functions,  21 — Histology  of  the  Human 
Body,  21— Physiologic  Chemistry,  21 — Arrangement  of  Topics,  22. 

I.  HISTOLOGY  OF  THE  HUMAN  BODY 23 

Cells,  23— Division  of  Cells,  28. 

Elementary  Tissues,  30— Epithelial  Tissue,  30— Connective  Tissue, 
34 — Areolar  Tissue,  34 — Adipose  Tissue,  35 — Ketiform  Tissue,  37 — 
Lymphoid  Tissue,  37— Elastic  Tissue,  37— Fibrous  Tissue,  38— Jelly- 
like  Tissue,  38 — Cartilage,  38— Bone,  41 — Dentin,  50— Muscular  Tissue, 
5G — Voluntary  Muscle,  56 — Involuntary  Muscle,  61 — Nervous  Tissue, 
63 — Nerve-fibers,  63 — Nerve-cells,  69 — Neuroglia,  72 — Development  of 
Nerve-cells  and  Nerve-fibers,  73 — Chemistry  of  Nervous  Tissue,  74. 

H.  PHYSIOLOGIC  CHEMISTRY    .'  .  .\ 76 

Inorganic  Ingredients,  77— Carbohydrates,  87— Fats,  99— Proteids, 
102 — Albumins,  107 — Albuminates,  109 — Globulins,  110 — Nucleopro- 
teids,  111 — Proteoses  and  Peptones,  113— Coagulated  Proteids,  113 — 
Poisonous  Proteids,  113 — Albuminoids,  115 — Enzymes,  117 — Metabo- 
lism, 120— Food,  121— Milk,  141— Mammary  Glands,  144— Eggs,  148— 
Meat,  150— Cereals,  153— Vegetables,  155— Beverages,  156— Effects  of 
Alcohol  upon  the  Human  Body,  158. 

in.  NUTRITIVE  FUNCTIONS ...  .  >  .   .   .    167 

DIGESTION 167 

Mouth  Digestion,  169 — Stomach  Digestion,  191 — Coats  of  the  Stom- 
ach, 192— Quantity  of  Gastric  Juice,  194 — Composition  of  Human 
Gastric  Juice  Mixed  with  Saliva,  195 — Action  of  the  Gastric  Juice, 
199— Movements  of  the  Stomach,  200— Vomiting,  205 — Excretory 
Function  of  the  Stomach,  208 — Effect  of  Nervous  Disturbances  upon 
Gastric  Digestion,  208 — Self-digestion  of  the  Stomach,  208 — Duration  of 
Stomach  Digestion,  209 — Removal  of  the  Human  Stomach,  211 — Achylia 
Gastrica,  219— Artificial  Gastric  Juice,  220— Effect  of  Alcohol  on  Di- 
gestion, 220 — Intestinal  Digestion,  221 — Structure  of  the  Small  Intes- 
tine, 221 — Structure  of  the  Large  Intestine,  227 — Succus  Entericus,  or 
Intestinal  Juice,  228 — The  Pancreas,  229— Structure  of  the  Pancreas, 
229— Pancreatic  Juice,  232— Innervation  of  the  Pancreas,  238— Internal 
Secretion  of  the  Pancreas,  239 — The  Liver,  239— Chemical  Composition, 
239— Structure,  240— Hepatic  Artery,  241— Portal  Vein,  241— Hepatic 

13 


14  CONTEXTS. 

DIGESTION — (Continued)  PAGE 

Duct,  242— Gall-bladder,  242— Bile,  244— Innervation,  250— Movements 
of  the  Small  Intestine,  250 — Digestion  in  the  Large  Intestine,  251 — 
Movements  of  the  Large  Intestine,  252 — Bacterial  Digestion,  253. 

ABSORPTION  OF  THE  FOOD; 254 

Mouth  Absorption,  254 — Gastric  Absorption,  254 — Absorption  by 
the  Small  Intestine,  255 — Glycogenic  Function  of  the  Liver,  256 — 
Formation  of  Glycogen  from  Carbohydrates,  257 — Formation  of  Gly- 
cogen  from  Proteids,  257 — Formation  of  Glycogen  from  Fats,  257 — 
Glycogenic  Theory,  257 — Diabetes,  259 — Absorption  of  Proteids,  260 — 
Absorption  of  Vegetable  and  Animal  Proteids,  261 — Absorption  of  Fat, 
261 — Absorption  by  the  Large  Intestine,  261. 

FECES  AND  DEFECATION 265 

Quantity  of  Feces,  265— Color  of  Feces,  266 — Eeaction  of  Feces, 
266— Composition  of  Feces,  266— Meconium,  266— Defecation,  266. 

BLOOD 268 

Physical  Properties  of  Blood,  268 — Distribution,  270 — Microscopic 
Structure,  270 — Blood-serum,  291 — Coagulation  of  Blood,  294— Regen- 
eration of  Blood,  299— Hemolysis  and  Bacteriolysis,  300. 

LYMPH 302 

Chemical  Composition,  302 — Histologic  Composition,  303— Origin, 
303— Chyle,  305. 

CIRCULATORY  SYSTEM 305 

The  Heart,  305— The  Arteries,  308— The  Capillaries,  310— The 
Veins,  310— Circulation  of  the  Blood,  311— Blood-pressure,  319— Rate 
of  Blood-flow  in  the  Vessels,  323— The  Pulse,  326— The  Plethysmo- 
graph,  329 — Circulation  in  the  Veins,  329. 

LYMPHATIC  SYSTEM ,...".. 330 

Lymphatic  Vessels,  330 — Lymphatic  Glands,  332 — Cavities  of  Serous 
Membranes,  333 — Circulating  Lymph,  334. 

DUCTLESS  GLANDS t 334 

The  Spleen,  335— The  Thyroid  and  Parathyroid,  339— The  Thymus, 
346— The  Suprarenal  Capsules  or  Adrenal  Bodies,  347— The  Pineal 
Gland,  351— The  Pituitary  Body,  351— The  Carotid  and  the  Coccygeal 
Glands,  352. 

RESPIRATION 352 

The  Nose,  353— The  Larynx,  354— The  Trachea,  361— The  Bronchi, 
362— The  Lungs,  362— The  Pleura,  365— The  Thorax,  365— Respiratory 
Movements,  372 — Capacity  of  the  Lungs,  374— Types  of  Respiration, 
375— Chemistry  of  Respiration,  376. 

VOICE  AND  SPEECH V  ....   «?.,. 389 

Laryngoscope,  390— Resonance,  391— Intensity,  392— Pitch,  392— 
Quality,  393— Registers,  393— Speech,  393— Vowels,  394— Consonants, 
394— Photography  of  the  Larynx,  394. 

VITAL  HEAT /  -   . \ 406 

Warm-blooded  Animals,  406 — Homoiothermal  Animals,  407 — Poikilo- 
thermal  Animals,  407 — Temperatures  of  Different  Animals,  407 — Tern- 


CONTENTS.  15 

VITAL  HEAT — Continued)  PAGE 

perature  of  Different  Parts  of  the  Body,  407— Temperature  at  Different 
Ages,  408— Daily  Variations  in  Temperature,  408 — Remarkable  Instances 
of  High  and  Low  Temperature,  408— Heat  Unit,  409— Sources  of  Vital 
Heat,  409 — Channels  Through  which  Vital  Heat  is  Lost,  410— Calor- 
imetry,  410 — Regulation  of  Temperature,  413. 

THE  SKIN 413 

Corium,  413 — Epidermis,  413 — Perspiratory  Glands,  413— Sebaceous 
Glands,  416— Cerumen,  417 — Hairs  and  Nails,  417 — Functions  of  the 
Skin,  418— Care  of  the  Skin,  419. 

THE  URINARY  APPARATUS 421 

The  Kidneys,  421— Ureters,  428— Bladder,  429 -Urethra,  430. 

THE  URINE 431 

Quantity,  431— Color,  431— Reaction,  431— Specific  Gravity,  432— 
Composition,  432 — Inorganic  Constituents,  440. 

IRRITABILITY;  CONTRACTILITY;   ELECTRIC  PHENOMENA  OF  MUSCLE  .    442 

IV.  NERVOUS  FUNCTIONS 460 

General  Considerations,  460— Nerves,  461— Nerve-impulses,  465 — 
The  Nervous  System,  468 — Spinal  Cord,  468 — Functions  of  the  Spinal 
Cord,  477— Reflex  Time,  479— Reflexes  in  Man,  479— Special  Centers 
in  the  Cord,  481— Functions  of  Spinal  Nerves,  482. 

THE  BRAIN 483 

The  Medulla  Oblongata,  484— The  Cerebellum,  491— The  Cerebrum, 
495 — Cranial  Nerves,  513. 

THE  SENSES 527 

General  Sensibility,  527 — Sense  of  Touch,  527— Sense  of  Pressure, 
529 — Muscular  Sense,  529 — Sense  of  Temperature,  529— Sense  of  Pain, 
530— Sense  of  Smell,  530— Olfactory  Nerves,  531— Olfactory  Bulb,  531— 
Olfactory  Tract,  533— Functions  of  the  Olfactory  Nerves,  533 — Sense  of 
Taste,  535— Circumvallate  Papillae,  536 — Conical  Papilla?,  537 — Fungi- 
form  Papillae,  537— Taste-buds,  537— Conditions  of  the  Sense  of  Taste, 
540— Sense  of  Sight,  541— Coats  or  Tunics,  541— Sclerotic  Coat,  541— 
Cornea,  541 — Choroid,  544— Ciliary  Processes,  545 — Iris,  545— Ciliary 
Body,  547 — Retina,  547 — Anterior  and  Posterior  Chambers,  554 — 
Vitreous  Body,  554 — Crystalline  Lens,  554 — Suspensory  Ligament, 
555 — Chemistry  of  the  Eye,  555— Ocular  Muscles,  556 — Physiology  of 
Vision,  560 — Defects  in  the  Visual  Apparatus,  570 — The  Iris,  575 — The 
Retina,  575— Light,  581— Form,  583— Identical  Points,  583— Size, 
583— Distance,  584 — Color,  587— Color-blindness  or  Daltonism,  593 — 
Fatigue  of  Retina,  594 — After-images,  594— Visual  Judgment,  595 — 
Appendages  of  the  Eye,  597 — Lacrimal  Apparatus,  597 — Meibomian 
Glands,  597— The  Sense  of  Hearing,  598— External  Ear,  598— Middle 
Ear,  600— Membrana  Tympani,  600— Tympanic  Cavity,  602— Ossicles, 
602— Eustachian  Tubes,  604— Mastoid  Anti-urn,  605— Fenestra  Ovalis, 
605— Fenestra  Rotunda,  606— Internal  Ear,  615 — Physiology  of  Hear- 
ing. 616— Theories  of  Hearing,  618— Period,  620— Amplitude,  620— 
Frequency,  620— Noises,  620— Musical  Sounds,  620— Intensity,  621— 
Loudness,  621— Pitch,  621— Quality,  621. 


16  CONTENTS. 

PAGE 

V.  REPRODUCTIVE  FUNCTIONS 624 

Reproductive  Organs,  624 — Genital  Organs  of  the  Male,  625 — 
Testes,  625— Penis,  630— Genital  Organs  of  the  Female,  631— Ovary, 
631— Fallopian  Tubes,  640— Uterus,  640— Ovulation,  642— Menstrua- 
tion, 645 — Formation  of  the  Corpus  Luteum,  649 — Maturation  of  the 
Ovum,  651 — Impregnation,  651 — Erection  of  the  Penis,  651 — Ejacu- 
lation, 652 — Ovarian  and  Abdominal  Pregnancy,  654 — Method  of 
Fertilization,  656— Segmentation,  657— Formation  of  the  Embryo, 
657 — Development  of  the  Chick,  658 — Membranes  of  the  Embryo, 
659— Amnion,  659— Yolk-sac,  660— Allantois,  660— Chorion,  660— 
Placenta,  660— Circulation  in  the  Embryo,  661 — Changes  in  the 
Circulation  at  Birth,  663. 


INDEX  ...  .    665 


HUMAN    PHYSIOLOGY. 


INTRODUCTION. 

Definitions. — Physiology  is  the  science  which  treats  of  func- 
tiom.  By  the  term  function  is  meant  the  characteristic  work 
performed  by  an  organ.  An  organ  may  be  defined  as  a  structure 
which  performs  a  function  or  functions,  for  the  special  or  char- 
acteristic work  of  an  organ  may  not  be  limited  to  a  single 
function :  thus  the  pancreas  secretes  not  only  pancreatic  juice, 
which  is  its  external  secretion^  but  also  another  product,  which  is 
its  internal  secretion  (p.  239).  Lifeless  things  perform  no  functions, 
hence  physiology  has  no  dealings  with  inanimate  things.  Rocks, 
stones,  and  other  members  of  the  mineral  kingdom  at  no  time 
possess  life ;  consequently  they  perform  no  functions,  and  with 
them  physiology  has  no  concern  :  we  cannot  speak  of  the  physi- 
ology of  minerals.  Plants  and  animals  are  sometimes  living  and 
sometimes  dead :  when  living  they  perform  functions,  when  dead 
they  perform  no  functions ;  in  the  latter  condition  they  are  like 
the  rocks  so  far  as  function  is  concerned,  and  with  them  physiology 
has  nothing  whatever  to  do.  It  is  only  when  they  are  living  that 
they  perform  functions,  and  it  is  then  and  only  then  that  with 
them  physiology  concerns  itself. 

Another  definition  which  might  be  given  of  physiology  is, 
that  it  is  the  science  which  treate  of  vital  phenomena.  A  brief 
consideration  of  this  definition  will  bring  us  to  the  same  conclu- 
sion as  did  that  of  the  preceding  definition.  Of  life  in  its  essence 
we  know  nothing.  Metaphysicians  have  endeavored  to  explain 
life,  and  some  have  even  ventured  to  point  out  its  seat,  but  the 
fact  remains  that  we  are  utterly  ignorant  of  its  nature.  We  only 
know  that  it  exists  by  certain  manifestations  which  it  presents. 
When  we  see  a  growing  plant  or  a  moving  animal,  we  say  of  each 
that  it  is  alive.  In  the  higher  forms  of  animals  and  plants  it  is 
easy,  under  ordinary  circumstances,  to  determine  whether  they  are 
living  or  not ;  but  in  the  lower  forms  this  determination  is  some- 
times a  most  difficult  task.  The  evidences  upon  which  reliance 
is  placed  to  determine  the  presence  or  the  absence  of  life  are 
spoken  of  as  vital  phenomena.  Thus,  if  in  examining  an  animal 
we  find  that  its  heart  beats,  we  say  that  the  animal  is  alive ;  but 
2  17 


18  INTRODUCTION. 

if  the  heart  is  motionless,  we  say  that  the  animal  is  dead.  This 
beating  of  the  heart,  therefore,  is  a  vital  phenomenon — that  is, 
a  manifestation  of  life.  We  speak  also  of  this  beating  of  the 
heart  as  its  function ;  hence  the  first  definition  of  physiology, 
that  it  is  the  science  which  treats  of  functions,  and  the  second 
definition,  that  it  is  the  science  which  treats  of  vital  phenomena, 
amount  to  the  same  thing. 

Definition  of  "Organ." — An  organ  has  already  been  defined  as 
a  structure  which  performs  a  function  or  functions.  In  speaking 
of  the  organs  of  an  animal  reference  is  usually  had  to  such  struct- 
ures as  the  heart,  the  lungs,  and  the  stomach,  inasmuch  as  their  size 
and  the  important  work  they  perform  force  them  upon  our  attention. 
These  are  indeed  organs,  for  they  perform  functions ;  thus  the 
function  of  the  heart  is  to  receive  blood  in  one  portion  and  to 
propel  it  from  another  portion,  that  of  the  lungs  is  to  aerate  the 
blood,  and  that  of  the  stomach  is  to  digest  certain  kinds  of  food ; 
but  the  term  organ,  as  used  in  physiology,  has  a  much  broader 
signification.  A  muscle,  a  nerve,  and  a  blood-vessel  are  as  truly 
organs  as  are  the  greater  ones  above  spoken  of,  for  each  has  its 
own  function.  Thus  the  function  of  a  muscle  is  to  contract,  that 
of  a  nerve  is  to  transfer  nervous  impulses,  and  that  of  a  blood- 
vessel is  to  convey  blood.  At  first  sight  it  might  seem  that  these 
functions  were  unimportant,  and  that  the  structures  which  per- 
formed them  were  hardly  worthy  of  so  dignified  a  name  as  organs ; 
but  a  moment's  reflection  will  show  that  without  the  contraction 
of  muscles,  the  transference  of  nervous  impulses,  or  the  carrying 
of  blood  the  life  of  an  animal  would  as  certainly  cease  as  if  it 
was  deprived  of  its  heart,  of  its  lungs,  or  of  its  stomach. 

Inasmuch  as  minerals,  on  the  one  hand,  possess  no  organs, 
they  perform  no  work — that  is,  they  have  no  functions ;  therefore 
we  do  not  speak  of  the  physiology  of  a  mineral.  Plants  and  ani- 
mals, on  the  other  hand,  possess  organs,  each  of  which  performs  its 
special  function  ;  and  it  is  with  them,  as  has  been  said,  that 
physiology  has  to  do.  As  we  find  organs  in  the  animal,  so  do  we 
find  them  in  the  plant ;  not  the  same  organs,  it  is  true,  but  struct- 
ures which  are  as  truly  organs,  for  they  respond  to  the  same  test. 
The  roots  of  a  plant  absorb  moisture  and  nourishment  from  the 
soil,  this  being  their  function ;  the  green  leaves  take  up  from 
the  air  carbonic  acid,  with  which  and  with  water  they  form  starch 
that  is  utilized  by  the  plant,  while  oxygen  is  set  free,  this  being 
the  function  of  the  leaves ;  the  anthers  and  the  ovaries  of  flowers 
are  concerned  in  reproducing  plants  by  forming  new  ones,  this 
being  their  function.  Thus  we  might  continue  to  show  that  as  in 
animals,  so  in  plants,  the  different  organs  have  their  respective 
functions. 

Definition  of 'Organic"  and  "Inorganic." — We  can  now  under- 
stand the  meaning  of  two  very  important  terms — organic  and 


BRANCHES  OF  PHYSIOLOGY.  19 

inorganic.  These  terms  are  used  in*  two  senses  :  first,  as  to  struct- 
ure, and,  second,  as  to  product.  When  we  say  that  a  plant  or  an 
animal  is  organic,  we  mean  that  it  is  made  up  of  organs — that  is, 
of  structures  which  perform  functions.  The  plant  or  the  animal 
may  be  simple  or  may  be  complex,  but,  however  simple  or 
however  complex,  its  parts  do  something,  that  something  being 
the  function  of  the  part  which  acts.  We  say,  therefore,  that 
the  plant  or  animal  is  organic,  meaning  that  it  is  composed  of 
organs — organic,  then,  as  to  structure.  The  rock  has  no  organs, 
therefore  it  is  non-organic,  or  is  inorganic.  These  terms  are  used 
also  in  another  sense.  Thus  we  speak  of  honey  as  organic.  Mani- 
festly, we  do  not  mean  organic  as  to  structure,  for  honey  has  no 
organs,  that  is,  no  parts  which  perform  functions,  but  it  is  the 
product  of  the  bee,  which  is  an  organic  structure ;  hence  honey 
is  an  organic  product.  The  nectary  of  a  flower  is  organic  as  to 
structure,  and  the  nectar  which  it  produces  is  also  organic, 
inasmuch  as  it  is  the  product  of  the  nectary. 

But  organs  do  not  act  each  for  itself:  they  are,  as  a  rule, 
associated  in  the  performance  of  a  common  function,  and  thus 
associated  form  a  system.  Thus  the  group  of  organs  which,  are 
concerned  in  digestion  forms  the  digestive  system  ;  those  which 
together  accomplish  the  circulation  of  the  blood,  the  circulatory 
system.  An  attempt  has  been  made  to  distinguish  an  apparatus 
from  a  system;  the  former  being  defined  as  a  group  of  organs 
concerned  in  the  performance  of  a  common  function,  no  matter 
how  dissimilar  their  structure,  while  organs  similar  in  structure 
irrespective  of  their  function  would  be  regarded  as  a  system. 
Similarity  of  function,  under  this  definition,  would  characterize 
an  apparatus,  and  similarity  of  structure  a  system.  The  organs 
whose  functions  are  to  digest  food  would  be  regarded  as  an  appa- 
ratus, constituting  the  digestive  apparatus  ;  the  bones,  on  the  other 
hand,  would  form  the  osseous  system.  Practically,  however,  such 
a  differentiation  is  of  no  use,  and  the  two  terms  apparatus  and 
system  may  therefore  be  used  interchangeably. 

Branches  of  Physiology. — From  these  elementary  con- 
siderations it  is  evident  that  physiology  has  to  do  with  living 
plants  and  animals  only — that  is,  with  organic  structures  and  inci- 
dentally with  their  products.  That  branch  of  the  science  which 
treats  of  the  functions  of  plants  is  denominated  Vegetable  Physi- 
ology, and  that  which  deals  with  the  functions  of  animals  is  called 
AnimaL  Physiology. 

Vegetable  Physiology. — We  are  concerned  but  indirectly  with 
vegetable  physiology,  or  so  far  only  as  its  study  helps  us  to  under- 
stand some  of  the  more  obscure  processes  in  animals.  Some  of  these 
processes,  being  simpler  in  plants,  are  more  easily  studied  in  them, 
and  what  is  there  learned  is  of  great  assistance  in  understanding 
analogous  processes  in  man.  Thus  a  knowledge  of  fertilization  as 


20  INTRODUCTION. 

it  occurs  in  the  vegetable  kingdom  aids  very  much  in  elucidating 
the  process  of  reproduction  in  the  human  species. 

Animal  Physiology. — The  same  organs  in  different  animals  per- 
form their  functions  in  different  ways.  Thus  the  stomach  of  the 
cow  and  that  of  the  dog  act  very  dissimilarly,  and  a  knowledge 
of  the  one  would  aid  very  little  in  acquiring  a  knowledge  of  the 
other.  What  is  true  of  the  stomach  is  true  of  other  organs  to  a 
greater  or  lesser  degree.  Each  class  of  animals  has  its  own  peculi- 
arities as  to  function — that  is,  has  its  own  physiology.  One  who 
intends  to  devote  his  life  to  the  treatment  of  the  diseases  of  the 
lower  animals  must  study  the  functions  of  those  animals,  while 
one  who  is  preparing  himself  for  the  cure  of  human  diseases  must 
understand  the  functions  of  the  organs  of  the  human  body,  or 
Human  Physiology. 

Many  hints,  it  is  true,  may  be  obtained  by  the  student  of 
human  physiology  from  a  study  of  the  processes  which  take  place 
in  the  lower  animals,  and  many  of  the  most  valuable  contributions 
made  to  physiologic  science  have  been  based  upon  such  a  study ; 
but  it  must  ever  be  borne  in  mind  that  specific  differences  exist, 
and  that  we  cannot  infer  too  much  from  such  observations.  Thus 
one  who  studies  the  process  of  stomach  digestion  in  a  ruminant, 
such  as  the  cow,  will  make  a  most  serious  blunder  should  he  sup- 
pose that  the  process  is  the  same  in  man.  Errors  of  a  similar 
character,  though  perhaps  less  glaring,  have  been  made,  notably 
in  the  process  of  reproduction.  This  process  is  so  obscure  that 
many  opportunities  which  have  presented  tnemselves  for  investi- 
gation, both  in  the  lower  and  in  the  higher  animals,  have  been 
seized  upon ;  but  theories  which  have  been  accepted  as  proved, 
and  which  have  largely  depended  on  such  observations,  are  now, 
in  the  light  of  more  recent  study,  being  questioned.  Notwith- 
. standing  this  disadvantage,  had  it  not  been  for  such  studies  many 
of  the  most  important  facts  of  medical  science  would  have  re- 
mained undiscovered.  Inasmuch  as  functions  cease  with  life, 
these  observations  can  only  be  made  upon  living  animals.  Vivi- 
section, therefore,  has  been  of  the  greatest  benefit  to  the  human 
race,  and  those  who  decry  it  are  daily  reaping  the  results  which 
it  has  attained,  and  which  could  never  have  been  attained  with- 
out it.  Wanton  and  unnecessary  experiments  are  to  be  condemned, 
but  no  terms  of  praise  are  too  exalted  to  bestow  upon  those  patient 
investigators  who,  through  many  long  years,  have  laboriously  and 
zealously  pursued  their  studies  and  experiments,  with  no  other 
end  in  view  than  to  add  to  the  sum  of  human  knowledge  and  to 
contribute  to  the  relief  of  human  suffering. 

Human  Physiology  Defined. — Human  physiology  is  the 
science  which  treats  of  the  human  functions.  This  science,  together 
with  anatomy,  which  treats  of  structure,  and  with  chemistry,  which 
treats  of  composition,  lies  at  the  foundation  of  rational  medicine. 


PHYSIOLOGIC  CHEMISTRY.  21 

No  one  can  be  a  successful  physician  who  does  not  understand 
at  least  the  more  important  functions  of  the  human  body,  and  the 
greater  the  knowledge  he  possesses  of  physiology,  the  broader  will 
be  the  scientific  groundwork  on  which  he  has  to  build.  Disease 
is  a  departure  from  the  normal  or  physiologic  condition.  A  dis- 
eased organ  performs  its  function  in  an  abnormal  manner,  and  to 
succeed  in  correcting  the  diseased  condition  one  must  first  be  able 
to  recognize  this  abnormal  action,  which  can  only  be  done  by 
knowing  how  the  organ  acts  in  health — that  is,  by  understanding 
its  physiology.  Even  with  this  knowledge  one  may  be  unable  to 
accomplish  the  desired  object,  for  the  structure  of  the  organ  may 
be  so  changed  that  no  means  can  be  applied  which  will  restore  it 
to  its  normal  condition  ;  but  one  is  certainly  more  likely  to  succeed 
if  possessed  of  a  knowledge  of  its  physiology  than  if  ignorant  of  it. 
The  study  of  human  physiology  is  but  the  study  of  the  human 
functions,  and  when  these  functions  are  thoroughly  understood 
the  science  is  mastered. 

Classification  of  Functions. — The  functions  of  the  body 
may  be  classified  as  follows  :  1.  Nutritive  Functions,  which  include 
those  concerned  directly  with  the  maintenance  of  the  individual, 
such  as  digestion,  respiration,  circulation,  etc. ;  2.  Nervous  Func- 
tions, which  include  those  that  bring  the  different  organs  of  the 
body  into  harmonious  relations  with  one  another,  and,  in  addition, 
bring  the  individual,  through  the  special  senses — sight,  hearing, 
etc. — into  relation  with  the  world  outside  him  ;  and  3.  Reproductive 
Functions,  which  are  concerned  not  with  the  individual,  but  with 
the  species,  which  they  perpetuate. 

Histology  of  the  Human  Body. — Anatomy,  as  we  have 
already  learned,  is  the  science  which  treats  of  structure ;  and  this 
is  true  as  well  of  the  minute  or  microscopic  as  of  the  gross  or 
macroscopic  structure ;  but  it  will  be  of  advantage  to  the  student 
of  physiology  to  have  distinctly  in  mind  so  much  of  the  histology 
or  minute  structure  of  the  body  as  is  necessary  to  a  full  under- 
standing of  its  functions,  and  to  appreciate  the  discussion  of  them. 
With  this  end  in  view,  the  histology  of  each  organ  will  be  given 
in  connection  with  its  function,  but  preliminary  to  all  this  we  shall 
discuss  the  tissues  of  the  body  which  go  to  make  up  these  organs. 
For  fuller  details  the  student  is  referred  to  the  many  excellent 
treatises  on  human  histology. 

Physiologic  Chemistry. — Although  physiology,  strictly 
speaking,  has  nothing  to  do  with  composition,  still,  as  a  matter 
of  necessity  as  well  as  of  convenience,  it  is  usual  to  preface  the 
study  of  the  functions  of  the  human  body  with  a  greater  or  lesser 
consideration  of  its  composition.  This  consideration  is  necessary, 
because,  as  a  rule,  medical  students  have  an  insufficient  knowledge 
of  this  branch  of  chemistry — physiologic  chemistry — to  take  up 
at  once  the  study  of  the  functions  with  profit,  and  should  the 


22  INTRODUCTION. 

attempt  be  made  confusion  and  loss  of  time  would  inevitably 
result.  As  an  illustration  we  may  refer  to  the  function  or  series 
of  functions  by  which  the  food  is  prepared  for  absorption — that  is, 
digestion.  Food  is  the  material  which  is  taken  into  the  body  to 
supply  the  waste  of  its  tissues,  and  it  must  be  of  such  a  composi- 
tion as  will  meet  this  want.  To  select  the  proper  food-materials 
we  must  know  of  what  the  body  is  composed,  and  what  are  the 
changes  which  take  place  in  its  composition — what  parts  are 
wasted.  For  these  reasons  a  study  of  physiologic  chemistry  must 
precede  a  study  of  the  functions  of  digestion.  This  is  but  one  of 
many  illustrations  which  might  be  given  to  show  the  importance 
of  prefacing  the  study  of  physiology  proper  with  a  study  of  the 
chemistry  of  the  body  and  of  the  food. 

Arrangement  of  Topics. — The  topics  treated  of  in  this  work 
will  therefore  be  arranged  in  the  following  order :  I.  Histology 
of  the  Human  Body.;  II.  Physiologic  Chemistry ;  III.  Nutritive 
Functions;  IV.  Nervous  Functions;  V.  Reproductive  Functions. 


I.  HISTOLOGY  OF  THE  HUMAN  BODY. 


ORGANS  on  minute  examination  are  found  to  be  made  up  of 
tissues,  or  elementary  tissues  as  they  are  sometimes  called. 

Of  elementary  tissues  there  are  four:  1.  Epithelial;  2.  Con- 
nective ;  3.  Muscular ;  and  4.  Nervous. 

Some  organs .  contain  all  four  kinds  of  tissues,  while  others, 
more  simple  in  their  structure,  contain  but  one  or  two. 

If  these  tissues  are  still  further  analyzed,  they  are  seen  to  con- 
sist of  cells  or  fibers,  or  of  both  together  in  varying  proportions : 
thus  the  epithelial  tissues  are  made  up  of  cells  alone ;  the  con- 
nective tissue,  principally  of  fibers ;  and  the  nervous,  of  both  cells 
and  fibers. 

Cells  (Fig.  1). — A  cell  consists  of  protoplasm,  a  nucleus,  and 
a  centrosome  and  attraction-sphere.  A  cell-membrane  enclos- 


Vacuoles. 


Chromatin  network 

Linin  network 
Nuclear  fluid 

Nuclear  membrane.  _Li 
Cell-membrane,  'i. 


Exoplasm.  _  _ 


Spongioplasm. 
Hyaloplasm. 

Nucleolus, 
Chromatin  net-knot. 

entrosome. 
Centrosphere. 


Foreign  mclosures.     Metaplasm. 
FIG.  1.— Diagram  of  a  cell  (Huber). 

ing  the  protoplasm   may  or  may  not  be  present;  it  is  not  an 
essential  part  of  a  cell  as  are  the  other  structures.    A  centrosome 

23 


24  CELLS. 

and  attraction-sphere  have  been  found  in  so  many  cells  that  they 
may  be  regarded  as  essential  constituents  of  every  cell. 

Protoplasm. — This  is  the  principal  part  of  a  cell,  and  is  of  an 
albuminous  nature.  Chemically  it  consists  of  water  (75  per  cent, 
or  more),  proteids,  lecithin,  cholesterin,  and  phosphates  and  chlo- 
rids  of  sodium,  potassium,  and  calcium,  and  sometimes  fat  and 
glycogen.  Microscopically  examined  it  is  found  to  be  made  up  of 
spongioplasrn  and  hyaloplasm. 

Spongioplasm. — Under  high  powers  of  the  microscope  the  pro- 
toplasm of  a  cell  presents  the  appearance  of  a  fine  network,  called 
reticulum,  spongework,  or  spongioplasrn.  This  network  has  in  it 
knots,  which  give  to  it  a  granular  appearance.  These  knots  or 
granules  are  of  the  same  chemic  nature  as  the  network — that  is, 
are  albuminous  or  proteid.  It  is  still  undecided  whether  these 
granules  are  constituent  parts  of  the  protoplasm  or  are  its  products. 
Collectively  they  are  denominated  granuloplasm.  Other  granules 
may  be  present  which  are  not  connected  with  the  network,  and 
which  are  not  proteid  in  character,  but  fatty  or  starchy  or  con- 
tain coloring-matter.  In  some  instances  they  are  of  an  inor- 
ganic nature.  Granules  of  this  latter  kind  constitute  paraplasm  ; 
by  which  is  meant  any  and  all  material  contained  in  a  cell,  not 
being  an  actual  part  of  it,  whether  there  as  pabulum  or  food  for 
the  cell,  or  as  waste  material  to  be  excreted. 

Hyaloplasm. — In  the  meshes  of  the  spongioplasm  is  the  hyalo- 
plasm,  a  clear  substance  differing  but  slightly  in  its  consistence 
from  the  spongioplasm,  although  it  is  less  solid. 

Ameboid  Movement. — Protoplasm  is  endowed  with  the  power 
of  motion,  which  from  its  resemblance  to  the  motion  of  the  ameba, 
a  minute  animal,  which  is  but  a  mass  of  protoplasm,  is  called 
ameboid.  .Examined  under  the  microscope  the  ameba  puts  out 
from  its  sides  projections  of  its  protoplasm — pseudopodia ;  and 
later  the  whole  mass  flows  into  one  or  more  of  these  projections, 
thus  changing  its  position  and  its  shape.  This  ameboid  movement 
takes  place  in  the  white  blood-corpuscle,  and  in  some  other  cells 
as  well  as  in  the  ameba.  The  pseudopodia  are  frequently  drawn 
back  into  the  protoplasm,  or  retract,  thus  illustrating  the  posses- 
sion by  the  protoplasm  of  contractility.  Their  formation  is  due  to 
an  outflowing  of  the  hyaloplasm,  and  their  retraction  to  return 
of  the  hyaloplasm  to  the  interstices  of  the  reticulum.  Ameboid 
movement  is  said  to  be  spontaneous ;  but  if  so,  it  can  also  be  pro- 
duced by  the  action  of  heat,  by  dilute  solutions  of  salt,  by  mod- 
erate currents  of  electricity,  and  by  many  other  agents,  all  of 
which  are  called  stimuli,  because  of  their  power  to  stimulate  this 
movement.  On  the  other  hand,  certain  agents  have  the  power  of 
stopping  or  inhibiting  the  movement  if  it  has  begun.  Thus  a 
temperature  above  40°  C.  or  below  0°  C.  acts  as  an  inhibitant, 
while  if  the  high  temperature  is  continued  the  protoplasm  is  coag- 


CENTROSOME.  25 

ulated  and  its  life  destroyed.  Acids  and  strong  alkalies  have  the 
power  of  destroying  the  movement  altogether,  while  chloroform 
inhibits  it  temporarily.  This  property  of  responding  to  a  stimulus 
is  known  as  irritability,  and  the  fact  that  a  stimulus  applied  to  one 
part  of  a  mass  of  protoplasm  will  produce  results  in  other  and 
distant  parts  demonstrates  the  presence  of  conductivity. 

Nutrition. — Another  property  possessed  by  living  protoplasm 
is  that  of  nutrition  ;  by  which  is  meant  the  power  to  absorb  mate- 
rial, to  convert  it  into  protoplasm,  and  to  get  rid  of  such  waste 
products  as  have  served  their  purpose  or  are  formed  as  a  result  of 
the  activity  of  the  protoplasm.  That  portion  of  the  process  which 
is  concerned  in  the  building  up  of  the  protoplasm  is  assimilation 
or  anabolism,  while  that  concerned  with  its  breaking  down  or 
destruction  is  disassimilation  or  katabolism. 

A  fourth  property  of  protoplasm  is  that  of  reproduction,  which 
will  be  treated  of  under  the  heading  Division  of  Cells. 

Nucleus. — Embedded  in  the  protoplasm  is  a  vesicle  of  various 
shapes — spherical,  oval,  or  irregular — which  is  to  be  regarded  as 
of  great  importance,  especially  in  the  process  of  cell-subdivision 
by  which  new  cells  are  formed  and  growth  thus  brought  about. 
It  consists  of  an  external  enveloping  membrane,  the  nuclear 
membrane,  enclosing  the  chromoplasm  or  intranuclear  network, 
a  material  resembling  spongioplasm,  and  in  the  interstices  of  this 
is  the  nuclear  matrix.  In  addition  to  these  there  are  nucleoli, 
some  of  which  are  thickenings  of  the  network  like  the  knots  in 
the  spongioplasm,  and  are  called  pseudonucleolij  while  others  are 
free,  the  latter  being  the  nucleoli  proper,  or  the  true  nucleoli.  A 
single  true  nucleolus  is  usually  found,  although  this  is  not  always 
the  case. 

Chromatin  and  Achromatin. — When  cells  are  stained  with  hema- 
toxylin  the  nuclear  membrane,  the  chromoplasm,  and  the  nucleoli 
take  up  the  staining-fluid  readily,  while  the  nuclear  matrix  does 
not ;  hence  the  former  are  said  to  be  made  up  of  chromatin,  or  to 
be  chromatic  ;  while  the  latter  is  achromatin,  or  is  said  to  be  achro- 
matic. Other  dyes,  such  as  safranin,  methyl-green,  and  carmine, 
produce  the  same  effect:  Chromatin  is  but  another  name  for 
nuclein,  which  is  the  principal  constituent  of  the  nucleus.  It  is 
closely  allied  to  the  proteids,  but  is  characterized  by  containing 
a  considerable  percentage  of  phosphorus ;  some  analyses  give  as 
much  as  8  per  cent.  Nuclein  is  a  compound  of  nucleic  acid  with 
proteids,  and  it  is  to  the  affinity  of  this  acid  for  the  coloring- 
matter  that  the  staining  of  chromatin  is  due.  It  is  more  correct  to 
speak  of  nucleins  rather  than  of  a  single  substance,  as  the  compo- 
sition of  nuclein  is  not  always  the  same.  For  a  further  discussion 
of  this  subject  the  reader  is  referred  to  the  chapter  dealing  with 
Proteids. 

Centrosome. — As  already  stated,  this  is  probably  to  be  regarded 


26 


CELLS. 


-Centrosome. 
-Centrosphere. 


-Chromosomes. 


,  Central 

spindle. 
-Nucleolus. 


Centrosome. 


Crown  of 
'    chromo- 
some. 


x  Crown  of 
chromo- 
some. 


FIG.  5. 


FIG.  6. 


FIG.  7. 


FIGS.  2-7. — Diagrammatic  representation  of  the  processes  of  mitotic  cell-  and 

nuclear  division  (Bohm  and  Davidoff). 
FIGS.  2-4,  Prophases ;  FIGS.  6,  7,  metaphases. 

FIG.  2,  Eesting  nucleus ;  FIG.  3,  coarse  skein  or  spirem ;  FIG.  4,  fine  skein  or 
spirem  ;  FIG.  5,  segmentation  of  the  spirem  into  single  chromosomes ;  FIG.  6,  longi- 
tudinal division  of  the  chromosomes ;  FIG.  7,  bipolar  arrangement  of  the  separated 
chromosomes. 


DIVISION  OF  CELLS. 


27 


Uniting 
filaments. 


FIG.  8. 


FIG.  9. 


FIG. 


FIGS.  8-12. — Diagrammatie  representation  of  the  processes  of  mitotic  cell-  and 

nuclear  division  (Bohm  and  Davidoff). 
FIGS.  8-11,  Anaphases ;  FIG.  12,  telophases. 

FIG.  8,  wandering  of  the  chromosomes  toward  the  poles;  FIG.  9,  diaster;  FIGS. 
10  and  11,  formation  of  the  dispirem ;  FIG.  12,  two  daughter-cells  with  resting 
nuclei.  To  simplify  the  figures  5-10,  we  have  sketched  in  only  a  few  chromosomes. 
In  Fig.  9  it  is  seen  that  the  cell-body  is  also  beginning  to  divide. 


28  CELLS. 

as  an  essential  element  of  the  cell,  inasmuch  as  the  more  the  sub- 
ject is  investigated  the  more  frequently  is  this  structure  found. 
It  is  also  known  by  the  name  of  attraction-particle.  Radiating 
from  it  as  a  center  are  fine  fibers,  which  together  with  it  constitute 
the  centrosphere  (Fig.  2).  Usually  there  are  two  of  these  spheres 
in  a  cell ;  especially  is  this  the  case  when  the  cell  is  about  to 
divide,  and  they  are  connected  by  fibers  forming  an  achromatic 
or  central  spindle. 

Division  of  Cells. — Cells  divide  and  then  multiply  in  two 
ways  :  1.  By  direct  division  ;  2.  By  indirect  division. 

Direct  Division  of  Cells. — This  may  be  either  by  gemmation  or 
by  fission.  In  the  former  a  portion  of  the  nucleus  and  proto- 
plasm forms  a  bud-like  projection  from  the  parent  cell,  from  which 
it  subsequently  separates.  The  bud  develops  into  a  cell  similar  in 
all  respects  to  that  from  which  it  had  its  origin.  In  fission  the 
original  nucleus  divides  into  two,  and  then  the  protoplasm  divides 
in  such  manner  that  each  half  shall  possess  its  own  nucleus,  and 
two  new  cells  are  thus  produced.  Direct  division  is,  however,  not 
the  method  by  which  cells,  as  a  rule,  reproduce  their  kind  ;  indeed, 
it  is  regarded  as  very  infrequent. 

Indirect  Division,  Karyokinesis,  Karyomitosis,  Mitosis  (Figs.  2-17). 
— It  is  to  this  method  of  division  that  we  must  look  for  the  com- 
prehension of  the  processes  by  which  the  tissues  produce  and  re- 
produce themselves.  It  has  been  studied  in  them  all — epithelial, 
connective,  muscular,  and  nervous.  While  in  direct  division  the 
nucleus  divides  into  two  equal  halves,  in  karyokinesis  the  changes 
which  take  place  in  the  nucleus  are  complicated,  and  it  is  only 
after  a  long  series  that  new  cells  are  produced. 

The  statement  is  made  by  some  authors  that  the  division  of 
a  cell  is  preceded  by  the  division  of  its  attraction-sphere,  and  that 
the  division  of  the  nucleus  follows ;  indeed,  some  regard  the  change 
taking  place  in  the  attraction-sphere  as  determining  or  causing  the 
division  of  the  nucleus ;  but  inasmuch  as  instances  have  been 
observed  in  which  the  nuclear  changes  preceded,  they  are  evidently 
not  under  all  circumstances  dependent  upon  the  influence  of  the 
attracti  on  -sphere . 

The  changes  which  take  place  in  the  process  of  karyokinesis 
may  be  concisely  described  as  follows  :  Prior  to  the  beginning  of 
the  process  the  cell  consists  of  protoplasm  containing  a  nucleus, 
with  one  or  more  contained  nucleoli,  and  enclosed  by  the  nuclear 
membrane,  and  a  centrosome  and  attraction-sphere.  A  close  ex- 
amination of  the  chromoplasm  of  the  nucleus  shows  it  to  be  made 
up  of  some  fibers  which  form  loops  at  the  ends  or  poles  of  the 
nucleus,  and  are  the  primary  loops,  while  others  less  prominent 
and  which  help  to  give  to  the  chromoplasm  its  reticular  or  net- 
work form  are  secondary  fibers. 

When  indirect  division  begins  the  first  change  usually,  though 


INDIRECT  DIVISION. 


29 


not  always,  consists  in  the  division  of  the  centrosome  and  of  the 
attraction-sphere  into  two ;  then  the  following  changes  take  place 
in  the  nucleus :  The  nucleoli  and  the  secondary  fibers  disappear, 
while  the  primary  loops  remain  as  chromosomes.  These  latter 
become  less  twisted,  forming  a  spirem  or  skein,  and  split  into  two 
sets,  forming  a  dispirem  or  double  skein,  thus  doubling  the  number 


FIG.  13. 


FIG.  14. 


FIG.  15. 


FIG.  16. 


FIG. 


FIGS.  13-17. — Mitotic  cell-division  of  fertilized  whitefish  eggs — Coregonus  albus 

(Huber). 

FIG.  13,  Cell  with  resting  nucleus,  centrosome,  and  centrosphere  to  the  right 
of  the  nucleus;  FIG.  14,  cell  with  two  centrospheres,  with  polar  rays  at  opposite 
poles  of  nucleus ;  FIG.  15,  spirem  ;  FIG.  16,  monaster ;  FIG.  17,  metakinesis  stage. 

of  chromosomes  (Fig.  10,  11).  The  number  of  chromosomes  is 
subject  to  considerable  variation  in  different  animal  cells.  In  some, 
four  have  been  seen,  in  others  as  many  as  twenty-four. 

The  achromatic  spindle  (Fig.  6)  now  appears.  This  consists 
of  a  spindle-shaped  structure,  at  each  end  of  which  is  a  centro- 
some, the  two  having  been  formed  from  the  original  centrosome 
of  the  cell.  These  are  connected  by  achromatin  fibers — i.  e.,  fibers 
which  are  not  colored  by  the  staining-material  used  in  the  study 


30  EPITHELIAL   TISSUE. 

of  the  karyokinetic  process.  Whether  these  fibers  are  formed 
from  the  attraction-sphere  or  from  the  achromatin  of  the  nucleus 
is  unknown.  Each  of  these  centrosomes  forms  a  pole  of  the 
spindle.  The  nuclear  membrane  now  disappears,  and  there  is 
nothing  between  the  protoplasm  of  the  cell  and  the  nuclear  matrix. 
The  protoplasm  in  contact  with  the  nucleus  is  clear,  while  that 
outside  of  this  clear  space  is  granular.  In  some  cells  these  gran- 
ules have  the  appearance  of  fine  fibers  radiating  from  the  centro- 
somes or  poles,  and  constitute  the  amphiaster. 

The  next  stage  is  characterized  by  the  settling  of  the  chromo- 
somes to  the  equator  of  the  spindle,  where  they  form  a  star  or 
aster,  which  being  single  is  called  monaster :  this  is  known  as  the 
equatorial  stage. 

The  chromosomes  now  separate  so  as  to  form  two  distinct 
groups,  constituting  the  stage  of  metakinesis.  One  group  passes 
to  one  end  or  pole  and  the  other  to  the  other,  thus  forming  a  star 
at  each  end  and  giving  rise  to  the  term  diaster  or  double  star. 
This  passage  of  the  chromosome  from  the  equator  to  the  poles  is 
believed  to  be  accomplished  by  the  contraction  of  the  achromatin 
fibers  of  the  spindle.  Thus  from  the  chromoplasm  of  the  nucleus 
two  new  nuclei,  or  daughter-nuclei,  are  formed,  each  aster  passing 
into  a  resting  nucleus  by  a  process  the  reverse  of  that  by  which  it 
was  formed,  through  the  dispirem  stage.  A  nuclear  membrane 
forms  around  each  new  nucleus,  and  the  protoplasm  of  the  original 
cell  subdivides  into  two,  each  half  enclosing  a  new  nucleus  :  at  the 
same  time  the  spindle  disappears. 


ELEMENTARY  TISSUES. 

EPITHELIAL  TISSUE, 

Distributed  over  the  surface  of  the  body,  lining  its  many 
cavities  and  canals,  and  in  the  ducts  of  glands,  epithelium  is 
found  of  several  varieties  and  arrangement.  The  varieties  are 
as  follows :  Pavement  or  scaly,  cubical,  columnar,  goblet-cell, 
spheroidal  or  glandular,  and  ciliated. 

Pavement  or  Scaly  Epithelium  (Fig.  18).— As  its  name 
implies,  the  cells  of  this  variety  of  epithelium  are  thin  and  flat, 
and  are  arranged  like  the  stones  of  a  pavement.  They  are  bound 
together  by  a  small  amount  of  cement-substance.  They  are  found 
in  the  lung-alveoli,  in  the  ducts  of  the  mammary  glands,  and  in 
the  kidney  in  the  tubes  of  Henle,  and  lining  Bowman's  capsules. 
These  cells  are  also  found  covering  serous  membranes,  as  the  peri- 
cardium, and  lining  blood-vessels  and  lymphatics,  and  in  that  case 
receive  the  name  of  endothelium. 

Cubical   Epithelium. — This   kind   of  epithelium   is   of  a 


COLUMNAR  EPITHELIUM. 


31 


cubical  shape,  and  occurs  in  the  tubules  of  the  testis  and  in  the 
alveoli  of  the  thyroid  gland. 


FIG.  18. — Isolated  cells  of  squamous  epithelium  (surface  cells  of  the  stratified 
squamous  epithelium  lining  the  mouth) :  a,  a,  cells  presenting  under  surface ; 
6,  cell  with  two  nuclei  (Huber). 

Columnar  Epithelium  (Fig.  20). — Columnar  epithelium  is 
sometimes  described  as  cylindrie  epithelium.  The  cells  are  of  a 
prismatic  shape,  and  usually  rest  upon 
a  basement-membrane.  When  looked 
at  from  the  free  end,  they  present  the 
appearance  of  a  mosaic ;  when  ob- 
served from  the  side,  the  free  edge 
is  seen  to  be  striated. 

This  variety  of  epithelium  lines 
the  stomach  and  intestines,  and  the 
glands  which  open  into  these  cavi- 
ties. It  covers  the  mucous  mem- 
brane of  most  of  the  urethra,  the  vas  FlG-  i9;-Surface  view  of  squa- 
-,  f,  ,-*  »  i  j  mous  epithelium  from  skin  of  a 

deferens,  prostate,  Cowper's   glands,     frog;  x400(B6hm  and  Davidoff). 
and  the  ducts  of  most  glands.    The 

germinal   epithelium   which    covers    the    ovary   is   of  this    type. 
Goblet-cell  (Fig.  22). — A  peculiar  modification  of  columnar 


Goblet-cell. 
Cuticular  border. 


FIG.  20. — Simple  columnar  epithelium  from  the  small  intestine  of  man :  o,  isolated 
cells  ;  b,  surface  view ;  c,  longitudinal  section  (Huber). 


32 


EPITHELIAL   TISSUE. 


epithelium  is  seen  in  the  goblet-cell.  This  occurs  in  the  intestine, 
for  example ;  the  mucin,  which  is  the  product  of  the  cell,  distends 
the  upper  part  of  it,  and  the  cell  bursts  (Fig.  22).  The  mucin  is 
discharged  as  mucus,  and  the  open,  cup-like  end  of  the  cell  gives 
to  it  the  peculiar  appearance  characteristic  of  the  goblet-cell. 


Goblet-cell. 


—Cilia. 


FIG.  21. — Cross-section  of  stratified  ciliated  columnar  epithelium  from  the  trachea 

of  a  rabbit  (Huber). 

Formerly  regarded  as  a  simple  modification  of  the  columnar  cell, 
these  goblet-cells  are  probably  more  properly  to  be  considered  as 
a  special  kind  of  epithelium  which  is  of  a  permanent  nature,  and 
whose  function  is  to  secrete  mucus;  hence  they  are  sometimes 
called  mucus-secreting  cells. 

Spheroidal  or  Glandular  Epithelium.— This  is  charac- 
terized by  its  polyhedral  or  spheroidal  shape,  and  occurs  in  secreting 


Nucleus... 


Basal  process  - 


FIG.  22. — Goblet-cells  from  the  bronchus  of  a  dog:  the  middle  cell  still  pos- 
sesses its  cilia :  that  to  the  right  has  already  emptied  its  mucous  contents  (collapsed 
goblet-cell) ;  X  600  (Bohm  and  Davidoff). 

glands ;  as,  the  salivary  glands,  liver,  and  pancreas.  The  secretion 
of  these  glands  is  the  product  of  the  protoplasm  of  the  glandular 
epithelium. 

Ciliated  Epithelium  (Fig.  23).— The  characteristic  of  this 
variety  is  the  cilia  or  hair-like  or  eyelash-like  appendages  attached 


CILIARY  MOTION. 


33 


-Cilia. 


Cell-body. 


•—.Nucleus. 


FIG.  23.— Ciliated  cells  from  the  bron- 
chus of  the  dog,  the  left  cell  with  two 
nuclei ;  X  600  (Bohm  and  Davidoff ). 


to  the  free  surface  of  the  cells.    The  cells  which  bear  the  cilia  are 
usually  of  the  cokimnar  variety. 

Ciliated  epithelium  covers  the  mucous  membrane  of  the  respir- 
atory tract,  which  begins  with  the  nose  and  ends  in  the  alveoli  of 
the  lung,  with  the  following  exceptions  :  The  olfactory  membrane 
(that  part  of  the/tnucous  mem- 
brane of  the  nose  to  which  the 
olfactory  nerves^are  distributed), 
the  lower  partf  of  the  pharynx, 
the  surfape  of  the  vocal  cords, 
the  ultimate  bronchi,  and  the 
lung-alveoli.  It  covers  also 
the  mucpus  membrane  of  the 
tympanum,  except  the  roof, 
promontory,  ossicles,  and  mem- 
brana  tympani,  where  the  epi- 
thelium is  of  the  pavement 
variety  and  non-ciliated.  Cil- 
iated epithelium  occurs  also  in 
the  Eustachian  tube,  the  Fal- 
lopian tube,  the  cavity  of  the 
body  of  the  uteVus  and  of  the  upper  two-thirds  of  the  cervix,  the 
vasa  eiferentia  and  coni  vasculosi  of  the  testicle,  the  ventricles 
of  the  brain,  and  the  central  canal  of  the  spinal  cord.  Some 
observers  have  seen  ciliated  epithelium  in  the  convoluted  tubules 
of  the  kidney. 

Ciliary  Motion. — Cilia  are  composed  of  protoplasm,  and, 
like  other  protoplasm,  have  the  power  of  motion ;  but  ciliary 
motion,  though  in  some  respects  like  that  known  as  ameboid,  is  in 
other  respects  quite  different.  Instead  of  being  slow,  it  is  very 
rapid — ten  times  and  more  a  second — so  much  so  that  when  active, 
the  individual  cilia  which  produce  it  are  indistinguishable.  It  has 
been  likened  to  the  movement  of  a  field  of  wheat  over  which  a 
breeze  is  passing.  The  effect  of  this  movement  is  to  produce 
a  current  always  in  one  direction,  and  this  current  is  often  of  con- 
siderable physiologic  importance :  thus  it  is  to  its  influence  that 
the  ovum  is  carried  down  the  Fallopian  tube  in  the  human  female  ; 
and,  according  to  some  authors,  were  it  not  for  the  ciliated  epithe- 
lium in  this  canal  the  ovum  would  not  find  its  way  into  the  tube, 
but  at  the  time  it  escapes  from  the  ovary  would  fall  into  the 
peritoneal  cavity  and  degenerate. 

Various  explanations  have  been  given  to  account  for  ciliary 
motion.  One  wl\ich  seems  reasonable  is  that  it  is  due  to  the  same 
cause  which  produces  ameboid  movement,  namely,  the  flow  of  the 
hyaloplasm  into  and  out  of  the  spongioplasm.  It  is  a  well-known 
fact  that  if  cilia  are  severed  from  the  cells  of  which  they  form 
a  part,  this  motion  ceases,  so  that  intimate  connection  with  the 


34  CONNECTIVE  TISSUE. 

cells  is  essential.  The  protoplasm  composing  the  cilia  being  thus 
in  direct  communication  with  that  of  the  epithelium,  being  in  fact 
a  prolongation  of  it,  the  hyaloplasm  can  flow  in  and  out  without 
hindrance ;  the  inflow  causing  them  to  straighten,  the  outflow 
causing  them  to  resume  their  original  condition,  which  is  curved ; 
this  rapid  inflow  and  outflow  produce  the  characteristic  motion. 

External  agencies  affect  this  motion  as  they  do  that  of  other 
protoplasm.  Chloroform  inhibits  it,  as  do  temperatures  above 
40°  C.  or  below  0°  C. ;  while  dilute  alkalies  favor  it. 

Simple  Epithelium. — When  epithelium  of  either  of  these 
varieties  is  arranged  in  a  single  layer  it  is  known  as  simple  epi- 
thelium. 

Stratified  Epithelium  (Fig.  21). — When  the  epithelial  cells 
are  arranged  in  many  layers  they  form  stratified  epithelium,  the 
cells  of  each  layer  differing  in  shape.  Thus  in  the  epidermis,  the 
epithelium  of  which  is  of  this  variety,  the  deepest  layer  is  columnar 
in  character ;  next  to  this  is  a  granular  layer  of  spindle-shaped 
cells ;  then  one  of  closely  packed  cells  ;  and,  most  superficial  of  all, 
are  several  layers  of  dry,  horny  scales'. 

Stratified  epithelium  is  also  found  covering  the  mucous  mem- 
brane of  the  mouth,  the  lower  part  of  the  pharynx,  the  esophagus, 
vagina,  and  outer  third  of  the  cavity  of  the  cervix  uteri,  and  the 
conjunctiva. 

Transitional  Epithelium. — This  term  is  applied  to  epithe- 
lium which  is  arranged  in  a  few  layers — two,  three,  or  four.  The 
line  of  demarcation  between  stratified  and  transitional  epithelium 
is  not  very  distinct.  This  variety  exists  in  the  ureters  and  bladder 
in  three  layers.  The  inner  layer  is  composed  of  cuboidal  cells, 
the  next  of  pear-shaped  cells,  between  the  lower  elongated  ends 
of  which  is  a  third  layer  of  small  cells. 

The  hair,  the  nails,  and  the  enamel  of  the  teeth  are  of  an 
epithelial  nature,  though  in  a  much  modified  form.  Epithelium 
is  nourished  by  lymph,  and  with  few  rare  exceptions  is  not  sup- 
plied with  nerves  :  such  exceptions  are  the  epithelium  covering  the 
cornea  and  that  in  the  deep  layers  of  the  epidermis. 

CONNECTIVE  TISSUE. 

The  term  "  connective  "  as  applied  to  this  large  group  of  tissues 
implies  that  they  are  concerned  in  binding  the  body  together  into 
one  organic  whole,  without  which  the  tissues  would  be  disconnected 
and  the  body  lack  the  support  which  these  structures  afford.  The 
following  are  the  varieties  :  1.  Areolar ;  2.  Adipose  ;  3.  Retiform  ; 
4.  Lymphoid  ;  5.  Elastic  ;  6.  Fibrous  ;  7.  Jelly-lfke ;  8.  Cartilage ; 
9.  Bone;  10.  Dentin. 

Areolar  Tissue. — Areolar  tissue  consists  of  bundles  of  fibers 
presenting  a  wavy  appearance  (Fig.  24)  running  in  various  direc- 


ADIPOSE  TISSUE. 


35 


tions,  together  with  elastic  fibers  (Fig.  25)  which  do  not  form 
bundles  and  are  not  wavy.  These  fibers  are  bound  together  by 
a  cementing-material  or  ground-substance.  The  irregular  crossing 
of  the  fibers  leaves  spaces,  called  areolse,  which  give  the  name  to 
the  tissue.  In  these  are  connective-tissue  cells  or  corpuscles,  of 
which  there  are  several  varieties,  the  protoplasm  of  which  pro- 
duces the  fibers  and  the  ground-substance.  These  varieties  are : 


FIG.  24. — Cell-spaces  in  the  ground-sub- 
stance of  areolar  connective  tissue  (subcu- 
taneous) of  a  young  rat;  stained  in  silver 
nitrate  (Huber). 


FIG.  25.— Elastic  fibers  from  the 
ligamentum  nuchae  of  the  ox,  teased 
fresh ;  X  500.  At  a  the  fiber  is  curved 
in  a  characteristic  manner  (Bohm 
and  Davidoff). 


1.  Lamellar  cells;  2.  Plasma-cells  of  Waldeyer;  3.  Granule-cells. 
Lymph-corpuscles  are  not  infrequently  seen,  and  in  some  places, 
as  in  the  choroid  coat  of  the  eye,  the  corpuscles  contain  coloring- 
matter  or  pigment. 

Areolar  tissue  occurs  under  the  skin  as  subcutaneous  tissue, 
beneath  serous  membranes  as  subserous,  and  beneath  mucous  mem- 


---.  Nucleus. 
L""  Protoplasm. 


Fat-drop. 
Cell-membrane. 


FIG.  26.— Scheme  of  a  fat-cell  (Bohm  and  Davidoff). 

branes  as  submucous,  connecting  these  membranes  loosely  to  the 
structures  upon  which  they  lie.  Enclosing  muscle,  blood-vessels, 
and  nerves,  it  forms  their  sheaths.  It  is  also  found  in  glands  con- 
necting the  various  parts  with  one  another. 

Adipose  Tissue  (Fig.  27).— When  the  areolae  of  areolar 
tissue  contain  fat-cells,  the  tissue  is  called  adipose.  These  fat- 
cells  or  adipose  vesicles  consist  of  an  envelope  or  sac,  protoplasmic 


36 


CONNECTIVE  TISSUE. 


in  character,  within  which  is  the  fat  in  a  fluid  form.     The  tem- 
perature of  the  body  during  life  is  believed  to  keep  this  fat  fluid ; 


FIG.  27. — Adipose  tissue  (Leroy ; :  a,  fibrous  tissue ;  6,  fat-cells ;  c,  nucleus  of  fat-cells ; 
d,  fatty  acid  crystals  in  fat-cells. 

but  after  death,  when  the   temperature   falls,  the   fat   becomes 
solid.    Free  adipose  vesicles  would  doubtless  assume  a  spheroidal 


4»-      ^ 


&  . 

BfliSl 


Li-'  • 


Reticulum. 


Nucleus  of 
connec- 
tive-tissue 
cell. 


Blood- 

vessel. 


FIG.  28. — Eeticular  connective  tissue  from  lymph-gland  of  man  ;   Brush  prepara- 
tion (Bohrn  and  Davidoffj. 

shape,    but    by    compression,    either    of   contiguous    vesicles    or 
other  structures,  they  assume  various  shapes,  oval  or  polyhedral. 


ELASTIC  TISSUE. 


37 


Adipose  tissue  is  widely  distributed  through  the  body;  indeed, 
it  is  an  exception  to  find  areolar  tissue  without  some  fat 
in  its  areolse.  The  principal  exceptions  are  the  areolar  tissue 
beneath  the  skin  of  the  eyelidst  the  penis,  the  scrotum,  and 
the  labia  minora.  There  is  also  no  adipose  tissue  within  the 
cranium,  in  the. liver,  or  in  the  lung,  except  near  its  root.  It 
is  to  be  understood  that  this  statement  does  not  apply  to  fat,  but 
to  adipose  tissue,  which  is  characterized  by  the  fact  that  the  fat 
is  enclosed  in  a  protoplasmic  envelope.  The  fat  is  formed  from 
the  protoplasmic  connective-tissue  corpuscles,  the  cell-wall  of 
which  forms  the  wall  of  the  vesicle.  The  nucleus  of  the  cell 
remains,  although  it  is  not  always  readily  discernible. 

Retiform  Tissue  (Fig.  28). — This  may  be  defined  as  areolar 
tissue  whose  ground-substance  is  fluid,  and  in  which  but  few,  if 
any,  elastic  fibers  exist,  and  the  white  fibers  form  a  close  network. 
Authorities  differ  as  to  the  identity  of  the  white  fibers  of  areolar 
and  those  of  retiform  tissue ;  some  claim  that  their  different  be- 
havior to  certain  reagents  demonstrates  them  not  to  be  the  same. 
Retiform  tissue  exists  in  mucous  membranes. 

I/ymphoid  Tissue. — When  the  areolae  of  retiform  tissue 
contain  lymph-corpuscles,  which  will  be  described  in  connection 
with  the  blood,  the  tis- 
sue is  lympkoid  or  ade- 
noid. It  is  found  in  lym- 
phatic glands,  the  thy- 
mus  gland,  the  tonsils, 
solitary  glands,  patches 
of  Peyer,  and  Malpigh- 
ian  corpuscles  of  the 
spleen. 

Elastic  Tissue 
(Fig.  25).— This  tissue 
is  composed  of  fibers  or 
membranes  which  are 
characterized  by  their 
elasticity  and  a  yellow 
color.  By  elasticity  is 
defined  "that  property 
of  matter  by  virtue  of 
which  a  body  tends  to 
return  to  a  former  or 

nnrm-il      <siyp      elmrkP      nr 

size,  snape,  or 
attitude,  after  being  de- 
flected or  disturbed."  The  tissue  exists  in  the  ligamenta  subflava 
of  the  vertebrae,  the  vocal  cords,  between  the  cartilages  of  the 
larynx%  in  the  longitudinal  coat  of  the  bronchi,  the  lungs,  the 
middle  coat  of  the  larger  arteries  (such  as  the  aorta  and  caro- 


Tendon-cell. 


—  Tendon-fibers. 


FIG.  29.— Longitudinal  section  of  tendon  ;  X  270 
(Bohm  and  Davidoff). 


38  CONNECTIVE  TISSUE. 

tids),  and  in  the  stylohyoid,  thyrohyoid,  and  cricothyroid  liga- 
ments. 

Fibrous  Tissue  (Fig.  29). — By  reason  of  its  color  this  kind 
of  tissue  is  also  called  white  fibrous  tissue.  It  is  made  up  of 
white  and  glistening  non-elastic  fibers,  which  give  to  it  great 
strength.  It  is  widely  distributed,  occurring  in  ligaments,  tendons, 
muscular  fascia,  periosteum,  perichondrium,  pericardium,  and  dura 
mater,  sclerotic  coat  of  the  eye,  tunica  albuginea  of  the  testis, 
capsule  of  the  kidney,  epineurium,  and  the  sheaths  of  the  corpora 
cavernosa  and  corpus  spongiosum  of  the  penis.  In  the  ligaments 
and  tendons  the  fibers  are  arranged  in  bundles,  between  which  are 
many  flat  connective-tissue  corpuscles,  the  tendon-cells  (Fig.  29). 


Matrix. — ££ 


C^,ag,-«p    ••    M    »     ||     |||j 


FIG.  30. — Hyaline  cartilage  (costal  cartilage  of  the  ox) ;  alcohol  preparation ; 
X  300  (Bohm  and  Davidoff ).  The  cells  are  inclosed  in  their  capsules.  In  the  figure 
a  are  represented  frequent  but  by  no  means  characteristic  radiate  structures. 

Jelly-like  Connective  Tissue.— This  consists  of  a  soft 
matrix,  with  a  few  spheroidal  cells  and  a  few  fibers.  It  is  found 
in  the  embryo,  as  in  the  jelly  of  Wharton  in  the  umbilical  cord. 
The  only  structure  in  the  adult  made  of  this  material  is  the 
vitreous  humor  of  the  eye.  It  consists  chemically  of  water  and 
mucinogen,  with  a  small  amount  of  proteid  and  salts. 

Cartilage. — This  tissue  exists  in  the  human  body  in  several 
varieties ;  a.  Hyaline ;  6.  White  fibrous ;  c.  Yellow  elastic  ;  d. 
Cellular. 

Hyaline  Cartilage  (Fig.  30). — This  variety  is  sometimes  called 
true  cartilage.  It  varies  in  structure  according  to  the  location  in 
which  it  occurs,  and  by  reason  of  this  its  location  receives  different 
names  :  articular  and  costal. 


CARTILAGE. 


39 


Articular  Cartilage  (Fig.  31). — The  cartilage-cells  of  this  vari- 
ety are  usually  arranged  in  small  groups  in  a  ground-substance  or 
matrix,  which  is  clear  except  when  examined  under  a  high  power 
of  the  microscope,  when  it  appears  granular.  In  this  matrix  there 
are  no  fibers  except  at  the  edges,  where  some  fibers  may  be  found 
and  where  the  cells  are  branched.  At  the  edges  the  cartilage  is  in 


White  fibrous  con- 
nective tissue. 


! 


White  fibrocarti- 
lage. 


^^H  f  Insertion  of  liga- 
" .«'    J     mentum  teres. 

'  < 


Hyaline  cartilage. 


FIG.  31. — Insertion  of  the  ligamentum  teres  into  the  head  of  the  femur ;  longi- 
tudinal section;  X  650  (Bohm  and  Davidoff). 


communication  with  the  synovia!  membrane  (Fig.  31),  and  the  cells 
of  the  cartilage  are  branched  and  resemble  the  branched  cells  of 
the  connective  tissue  of  the  synovial  membrane,  from  which  fact 
they  give  to  the  cartilage  the  name  transitional.  Although  hyaline 
cartilage  is  described  as  having  a  matrix  free  from  fibers,  still, 
under  proper  treatment,  a  fibrous  character  can  be  made  out. 

Articular   cartilage   covers  the   ends  of  bones   in   the  joints 


40  CONNECTIVE  TISSUE. 

Fig.  31),  where  it  serves  the  double  purpose  of  reducing  concussion 
by  virtue  of  its  elasticity,  and  of  forming  a  smooth  surface  for  the 
motion  of  the  joint.  It  has  no  blood-vessels,  but  is  nourished  from 
both  the  synovial  membrane  and  the  bone.  It  does  not  ossify — 
that  is,  become  bone. 

Costal  Cartilage  (Fig.  30). — Cartilage  of  this  kind  is  hyaline, 
though  in  old  age  a  fibrous  character  is  observed.  Its  individual 
cells  are  larger,  and  the  groups  of  them  are  larger  than  in  articular 
cartilage.  Its  tendency  to  ossify  is  another  difference  when  com- 
pared with  the  articular  variety.  Ossification  and  calcification 
must  be  very  carefully  distinguished.  In  the  former  a  formation 


•Cartilage-cell. 


Elastic  fibers. 


FIG.  32.— Elastic  cartilage  from  the  external  ear  of  man :  a,  fine  elastic  network  in 
the  immediate  neighborhood  of  a  capsule  ;  X  760  (Bohm  and  Davidoff). 

of  bone  occurs ;  in  the  latter  there  is  simply  a  deposition  of  lime 
salts. 

Costal  cartilage  is  found  in  connection  with  the  ribs,  and  also 
in  the  larynx,  excepting  in  those  minute  structures,  the  cornicula 
laryngis  or  the  cartilages  of  Santorini.  It  also  forms  the  carti- 
laginous structure  in  the  trachea,  the  nose,  and  the  external  audi- 
tory meatus. 

White  Fibrous  Cartilage  or  Fibrocartilage  (Fig.  31). — White 
fibrous  connective  tissue,  with  cartilage-cells  between  the  bundles, 
characterizes  this  tissue.  It  is  described  as  of  four  kinds,  principally 
by  reason  of  the  office  it  serves ;  inter  articular,  flat  plates  between 


BONE.  41 

the  articular  cartilages  of  some  joints,  as  the  knee  and  the  wrist ; 
connecting ,  as  between  the  bodies  of  the  vertebrae ;  circumferential, 
as  in  the  cotyloid  cavity  of  the  hip-joint,  which  it  makes  deeper ; 
and  stratiform,  where  it  lines  grooves  in  bone  through  which 
tendons  pass.  It  also  occurs  in  some  tendons,  as  in  that  of  the 
peroneus  longus. 

Yellow  Elastic  Cartilage  (Fig.  32). — The  presence  of  elastic 
fibers  in  the  matrix  is  the  distinguishing  feature  of  this  variety  of 
cartilage,  which  is  found  in  the  pinna  of  the  ear,  the  Eustachian 
tube,  the  epiglottis,  and  the  cornicula  laryngis. 

Cellular  Cartilage. — This  kind  is  made  up  almost  wholly  of  cells ; 
sometimes  fine  fibers  are  present.  The  only  structure  in  which  it 
is  found  in  the  human  body  is  the  chorda  dorsalis  or  notochord  of 
the  embryo. 

Chemical  Composition  of  Cartilage. — The  following  analyses 
were  made  by  Hoppe-Seyler,  and  represent  parts  per  1000 : 

Costal  Cartilage.  Articular  Cartilage. 

Water ;   . 676.6  735.9 

Solids,  organic 301.3  248.7 

Solids,  inorganic .    .    .      22.0  15.4 

999.9  1000.0 

Organic  Solids  of  Cartilage. — The  cells  contain,  besides  the 
proteid  contents  of  cells  generally,  fat  and  glycogen.  The  matrix 
contains  chondrigen,  which  on  boiling  yields  chondrin.  This  is 
the  generally  accepted  theory  as  to  cartilage,  but  the  most  recent 
analyses  seem  to  show  that  chondrin  is  not  a  simple  substance,  but 
a  mixture,  and  that  in  the  matrix  are  four  substances :  1.  Col- 
lagen ;  2.  An  albuminoid,  which  exists  only  in  later  adult  life,  and 
is  like  elastin,  but  contains  more  sulphur ;  3.  Chondromucoid  ;  and 
4.  Chondroitin-sulphuric  acid. 

Inorganic  Solids  of  Cartilage. — Potassium  and  sodium  sul- 
phates, sodium  chlorid,  and  sodium,  calcium,  and  magnesium 
phosphates  represent  the  inorganic  class  of  physiologic  ingredients 
of  cartilage. 

Perichondrium. — This  is  a  fibrous  membrane  which  envelops 
cartilage  except  at  the  articular  ends  of  bones  :  it  contains  blood- 
vessels, which  assist  in  nourishing  the  cartilage. 

Bone. — There  are  two  varieties  of  bone :  compact  and  can- 
cellous  or  cancellated.  The  former  is  firm  and  dense,  and  occurs 
on  the  exterior  of  bones ;  the  latter  is  spongy  and  more  open  in 
structure,  and  occupies  the  interior.  The  differences  between  the 
two  are  not  such  as  to  justify  their  being  regarded  as  two  distinct 
varieties,  for  in  all  essential  points  they  are  identical.  Practically, 
however,  it  seems  wise  to  describe  them  separately.  When  a 
cross-section  of  a  bone  is  examined  under  the  microscope  (Fig.  33) 
Haversian  canals  are  seen,  averaging  0.05  mm.  in  diameter : 


42 


CONNECTIVE  TISSUE. 


around  these  the  bone  is  arranged  in  rings,  lamellae;  between 
these  are  spaces,  lacunae,  in  which  are  bone-corpuscles  (Fig.  34). 
Each  canal  is  connected  with  the  lacunae  which  are  concentric 


- 


•<*.• 


~  I  HT'.'.JL:  ' 
M*       icrTfrvi     T;^*^-1  r 


ip^^l^pS 


Outer  circum- 
ferential 
lamellae. 


Haversian  or 
concentric 
lamellae. 


ll?Rli|S;  if 

//,•  r^^-v*>:^^.s--"' 


Inner  circum- 
ferential 
lamellae. 


FIG.  33. — Segment  of  a  transversely  ground  section  from  the  shaft  of  a  long 
bone,  showing  all  the  lamellar  systems ;  metacarpus  of  man ;  X  56  (Bohni  and 
Davidoff). 

with  it,  and  the  lacunae  with  one  another  by  means  of  fine  canals, 
canaliculi,  into  which  project  processes  of  the  bone-corpuscles. 
A  Haversian  canal  (Fig.  34)  with  its  lamellae,  lacunae,  bone- 


BONE.  43 

corpuscles,  and  canaliculi  form  a  Haversian  system.  In  a  section 
of  bone  several  of  these  systems  may  be  seen,  the  spaces  between 
them  being  occupied  by  interstitial  lamellce.  Lamellae  which  are 
on  the  surface  of  the  bone,  parallel  with  its  circumference,  are 
circumferential  lamellce.  A  longitudinal  section  of  bone  shows 
the  Haversian  canals  to  be  what  their  name  indicates,  channels 
running  through  the  bone.  Their  communication  with  one  another 
is  also  seen.  In  each  canal  are  an  artery  and  a  vein. 

If  a  piece  of  bone  is  treated  with  dilute  nitric  acid,  so  as  to 
dissolve  the  lime  salts  which  it  contains,  or  by  some  other  method 
of  decalcification,  a  small  portion  may  be  torn  off,  which  upon 
examination  shows  the  fibrous  structure  of  the  lamellae.  Such 
specimens  also  show  the  perforating  fibers  of  Sharpey,  which 
hold  the  lamellae  together;  elastic  fibers  may  also  be  observed. 


Lacuna." 
Canaliculi. 

Haversian  canal.  •• 


FIG.  34.— Portion  of  a  transversely  ground  disk  from  the  shaft  of  a  human  femur; 
X  400  (Bohm  and  David  off). 

Periosteum. — This  is  a  fibrous  membrane  which  encloses  the 
bones  except  where  covered  by  cartilage.  It  is  made  up  of  an 
outer  layer  of  connective  tissue,  in  which  there  are  blood-vessels 
which  give  off  branches  that  go  to  the  Haversian  canals  ;  and  an 
inner  layer,  in  which  elastic  fibers  are  present.  Between  the  peri- 
osteum and  the  bone  in  young  animals  are  nucleated  cells,  the 
osteoblasts  or  bone-forming  cells. 

Bone-marrow. — Marrow  is  of  two  kinds,  yellow  and  red.  The 
yellow  marrow  is  found  in  the  interior  of  the  shafts  of  long  bones, 
in  the  medullary  canal,  and  consists  of  fibrous  tissue  in  which  are 
blood-vessels  and  cells,  fat-cells  principally,  although  some  marrow- 
cells  and  myeloplaxes  also  occur.  The  composition  of  yellow  mar- 
row is  :  fat,  96  per  cent,  (no  other  structure  of  the  body  containing 
so  much,  adipose  tissue  containing  but  82.7  per  cent.)  ;  areolar 
tissue,  1  per  cent. ;  and  3  per  cent,  of  fluid.  Red  marrow  (Fig.  35) 
occurs  in  flat  and  short  bones,  the  articular  ends  of  long  bones, 
bodies  of  vertebrae,  cranial  diploe,  sternum,  and  ribs.  In  structure 
it  resembles  yellow  marrow,  except  that  fat-cells  are  few,  while 
marrow-cells  are  very  abundant.  Chemically  it  is  composed  of 


44  CONNECTIVE  TISSUE. 

75  per  cent,  water  and  25  per  cent,  solids ;  the  latter  consisting 
of  salts,  a  very  small  amount  of  fat,  and  two  proteids,  one  a  cell- 
globulin  coagulating  at  47°-50°  C.  and  a  nucleoproteid  containing 
1.6  per  cent,  of  phosphorus.  Hemoglobin  is  also  present. 

Marrow-cells  (Fig.  36). — The  cells  of  red  marrow  are  of  four 
kinds :  1.  True  marrow-cells,  which  are  round,  nucleated  cells  like 
white  blood-corpuscles,  but  larger,  and  exhibiting  ameboid  motion. 
2.  Erythroblasts,  pinkish  in  color,  and  in  appearance  like  the  nucle- 
ated red  blood-corpuscles  of  the  embryo.  Some  authorities  regard 
these  latter  as  cells  which  are  originally  true  marrow-cells  and 
afterward  become  red  blood- corpuscles;  while  others  hold  that 
they  are  never  marrow-cells,  but  have  come  directly  from  the 
nucleated  blood-cells  of  the  embryo  and  become  red  blood- 
corpuscles,  the  nuclei  disappearing.  In  the  erythroblasts  the 
process  of  karyokinesis  may  often  be  observed.  3.  Myeloplaxes ; 
these  cells  are  also  called  giant  cells,  myeloplagues,  and  osteoclasts* 
These  are  very  large  nucleated  cells,  which  are  also  found  in  the 
yellow  marrow  of  the  adult.  4.  Cells  which  contain  red  blood- 
corpuscles  in  various  stages  of  transformation  into  pigment,  resem- 
bling the  large  cells  found  in  the  spleen,  and  called  splenic  cells. 

Blood-vessels  of  Bone. — The  periosteum  sends  branches  of  its 
blood-vessels  into  the  compact  tissue,  some  passing  into  the  Haver- 
sian  canals,  while  others  continue  on  and  supply  the  cancellous 
tissue  in  the  interior.  In  the  middle  of  the  long  bones  is  an 
opening,  the  nutrient  foramen,  through  which  passes  the  medullary 
or  nutrient  artery,  with  one  or  two  veins,  traversing  the  compact 
tissue  to  reach  the  medullary  canal,  where  it  supplies  the  tissue 
contained  therein.  Similar  openings  exist  in  other  bones  for  the 
transmission  of  blood-vessels  to  their  interior.  It  is  claimed  by 
some  that  the  walls  of  the  capillaries  in  the  marrow  are  imperfect, 
and  that  through  the  openings  which  exist  the  red  blood-corpuscles 
produced  in  the  marrow  find  their  way  into  the  blood-circulation. 

Lymphatic  Vessels  of  Bone. — These  are  found  in  the  periosteum 
and  the  bone-substance,  and  also  in  the  Haversian  canals. 

Nerves  of  Bone. — The  periosteum  is  supplied  with  nerves,  and 
they  also  pass  into  bones  through  the  nutrient  foramina,  Espe- 
cially rich  in  nerves  are  the  articular  extremities  of  long  bones, 
the  vertebrae,  and  the  larger  flat  bones. 

Chemical  Composition  of  Bone. — Hoppe-Seyler  gives  the  follow- 
ing analysis  of  undried  bone  without  separation  of  marrow  or  blood : 
Water 50.00  per  cent.  Ossein  (or collagen ).  .  11.40  per  cent. 


Fat  .        ...  .   15.75 


Bone  earth 21.85 


The  following  is  Zalesky's  analysis  of  human  dried  macerated 
bone : 

Organic  constituents 34.56  per  cent. 

Inorganic        "  ,   .    .    .    65.44    "      " 

100.00 


BONE. 


45 


Gray  states  that  the  organic  constituent  of  bone  forms  about 
33  per  cent.,  and  the  inorganic  66.7  per  cent.  He  quotes  the  fol- 
lowing analysis  of  Berzelius  : 


Organic  matter  ... 


.   Gelatin  and  blood-vessels  . 

(Phosphate  of  lime  .  .  .  . 
Carbonate  "  .... 
Fluorid  of  calcium  ... 
Phosphate  of  magnesium  . 
Soda  and  chlorid  of  sodium, 


33.30  per  cent. 

51.04 

11.30 

2.00 

1.16 

1.20 


The  organic  constituents  are  ossein,  also  called  collagen  ;  elas- 
tin,  proteids,  and  nuclein  form  the  bone-corpuscles,  with  a  small 
quantity  of  fat.  The  inorganic  constituents  are  calcium  phosphate, 


\ 


4 


- 


FIG.  35. — From  a  section  through  human  red  bone-marrow :  a,  /,  normoblasts ; 
6,  reticulum  ;  c,  mitosis  in  giant  cell ;  d,  giant  cell ;  e,  h,  myelocytes  ;  g,  mitosis ; 
i,  space  containing  fat-cells ;  X  680  (Bohm  and  Davidoff ). 

carbonate,  chlorid,  and  fluorid ;  magnesium  phosphate,  sodium 
chlorid,  and  some  sulphates.  Of  these  inorganic  constituents, 
calcium  phosphate  exists  to  the  amount  of  83.88  per  cent.,  and 
calcium  carbonate  to  the  amount  of  13  per  cent. 

Development  of  Bone. —  Ossification,  the  process  by  which  bone 
is  formed,  occurs  in  two  forms :  intramembranous  and  intracarti- 
laginous  or  endochondral.  The  subperiosteal  variety  described  by 
some  authors  is,  in  all  essential  particulars,  identical  with  the 
intramembranous.  By  the  intramembranous  are  formed  the 
parietal,  frontal,  and  upper  portions  of  the  tabular  surface  of  the 


46  CONNECTIVE  TISSUE. 

occipital  bone ;  while  by  the  intracartilaginous,  the  humerus, 
femur,  and  other  long  bones  are  formed. 

Intramembranous  Ossification  (Fig.  37). — This  process  may  be 
studied  in  the  parietal  bone,  which,  prior  to  the  beginning  of 
ossification,  about  the  seventh  or  eighth  week  of  fetal  life,  is  a 
fibrous  membrane  containing  blood-vessels  and  osteoblasts  (Fig. 
37).  The  process  begins  in  the  center  of  ossification,  which,  in  the 
parietal  bone,  is  single,  at  the  parietal  eminence.  The  number  of 
these  centers  varies  in  different  bones ;  in  the  frontal  there  are 
two. 

The  embryonic  membrane  is  composed  of  bundles  of  fibers, 
osteogenic  fibers,  with  a  granular  matrix  between  them.  Both  the 


t- 


FIG.  36. — Cover-glass  preparation  from  the  bone-marrow  of  dog ;  X  1200  (from 
preparation  of  H.  F.  Miiller)  (Bohm  and  Davidoff) :  a,  mast-cell;  6,  lymphocyte; 
c,  eosinophile  cell ;  d,  red  blood-cell ;  e,  erythroblast  in  process  of  division  ;  /,  /,  nor- 
moblast ;  g,  erythroblast.  Myelocyte  not  shown  in  this  figure. 

fibers  and  the  matrix  become  calcified  by  the  deposition  in  them 
of  lime  salts,  and  there  is  produced  in  them  a  calcareous  mass 
enclosing  blood-vessels  and  osteoblasts,  which  latter  become  bone- 
corpuscles,  and  the  spaces  in  which  they  lie  form  the  lacunae.  The 
blood-vessels  permeate  the  whole,  the  channels  which  they  form 
being  Haversian  canals.  It  will  be  observed  that  in  this  variety 
of  ossification  a  membranous  structure  precedes  the  bone ;  hence 
the  bone  is  said  to  Reformed  in  membrane. 

Intracartilaginous  or  Endochondral  Ossification  (Fig.  37). — In 
this  form  cartilage  precedes  the  bone,  and  the  changes  which  result 
in  bone-formation  take  place  within  it  and  practically  convert  it 
into  bone. 

First  Stage. — In  the  first  stage  the  cartilage-cells  at  the  center 


BONE. 


47 


Connective 
tissue. 


Marrow 

space. 

Blood-  ves- 
sel. 


Osteobla 


Osteoblasts. 


FIG.  37.— From  a  cross-section  of  a  shaft  (tibia  of  a  sheep) ;  X  550  (Bohm  and 
Davidoff) :  in  the  lower  part  of  the  figure  is  endochondral  bone-formation  (the 
black  cords  are  the  remains  of  the  cartilaginous  matrix) ;  in  the  upper  portion  is 
bone  developed  from  the  periosteum. 

of  ossification  become  larger  and  arranged  in  rows ;  in  the 
matrix  or  ground-substance,  between  these  rows  of  cells,  lime 
salts  are  deposited  in  such  manner  as  to  form  longitudinal  rows 
of  cells,  separated  by  the  calcified  matrix ;  in  the  matrix,  between 


48 


CONNECTIVE  TISSUE. 


adjacent  cells,  at  right  angles  to  these  calcareous  columns,  lime 
salts  are  also  deposited,  thus  forming  spaces  containing  cartilage- 
cells,  the  boundaries  of  which  are  composed  of  the  calcified  matrix. 
These  spaces  or  cavities  are  primary  areolce.  While  this  process 
is  taking  place  at  the  center  of  the  cartilage,  beneath  the  mem- 
brane which  envelops  the  cartilage,  the  perichondrium,  or,  as  it  is 
subsequently  called,  the  periosteum,  the  osteoblasts  form  fibrous 


Vesicular  cartilage- 
cells. 

Primary  periosteal 
bone-lamella. 


_„  Periosteal  bud. 


Periosteum. 


Unaltered  hyaline 
cartilage 


FIG.  38. — Longitudinal  section  through  a  long  bone  (phalanx)  of  a  lizard  embryo 
(Bohm  and  Davidoff).  The  primary  bone-lamella  originating  from  the  periosteum 
is  broken  through  by  the  periosteal  bud.  Connected  with  the  bud  is  a  periosteal 
blood-vessel  containing  red  blood-corpuscles. 

lamellae  on  the  surface  of  the  bone,  which  become  calcified  by  the 
deposit  in  them  of  lime  salts.  Some  osteoblasts  are  closed  in  by 
the  lamellae  and  become  bone-corpuscles.  These  changes  which 
take  place  on  the  surface  beneath  the  periosteum  constitute  sub- 
periosteal  or  intramembranous  ossification,  which  has  already  been 
described ;  thus,  both  kinds  of  ossification  take  place  in  the  long 
bones. 


BONE. 


49 


Second  Stage  or  Stage  of  Irruption. — In  this  stage  the  blood- 
vessels and  osteoblasts  of  the  periosteum  form  processes  which 
absorb  portions  of  the  bone  recently  made  by  intramembranous 
ossification,  and  of  the  walls  of  the  primary  areolae,  thus  pro- 
ducing larger  spaces  or  cavities,  sec- 
ondary areolce  or  medullary  spaces; 
these  contain  osteoblasts  and  blood- 
vessels, which  constitute  embryonic 
marrow.  Authorities  differ  as  to  the 
ultimate  fate  of  the  cartilage-cells; 
some  think  they  become  osteoblasts, 
while  others  teach  that  they  are  ab- 
sorbed. 

Third  Stage. — The  osteoblasts  of  the 
embryonic  matrix,  increased  in  num- 
ber by  division,  form  a  layer  of  bone 
on  the  surfaces  of  the  walls  of  the 
secondary  areolse.  On  this  bony  wall 
another  layer  of  osteoblasts  forms  a 
second  layer  of  bone,  and  thus  the 
process  continues  until  only  a  small 
canal  remains,  the  Haversian  canal. 
The  layers  of  bone,  produced  in  the 
manner  described,  are  the  lamellae; 
while  such  of  the  osteoblasts  as  remain 
between  the  lamellae  become  the  bone- 
corpuscles.  No  satisfactory  explanation 
has  been  given  of  the  method  of  pro- 
duction of  the  canaliculi.  During  this 
stage  the  process  of  ossification  which 
began  in  the  center  of  the  bone  extends 
toward  the  extremities,  and  thus  the  en- 
tire shaft  becomes  ossified.  Histologists 
describe  the  multinucleated  cells  (sim- 
iliar  to  the  myeloplaxes  of  the  marrow) 
which  are  concerned  in  the  absorption 
of  the  calcified  matrix  and  bone  under 
the  name  osteoclasts,  reserving  the  term 
osteoblasts  for  the  cells  which  form  the 
bone. 

The  shaft  of  the  bone  and  its  ex- 
tremities remain  separated  for  a  period 
of  time  which  varies  in  different  bones, 
and  increase  in  length  takes  place  by  a  growth  of  cartilage  between 
the  shaft  and  its  epiphyses.  This  intermediate  cartilage  later  ossi- 
fies, and  the  union  of  shaft  and  extremities  is  complete.  Cartilagi- 
nous at  first  like  the  shaft,  the  epiphyses  undergo  ossification  in 


FIG.  39. — Longitudinal  sec- 
tion through  area  of  ossifica- 
tion from  long  bone  of  human 
embryo  (Huber). 


50 


CONNECTIVE  TISSUE. 


/ 


Enamel. 


SHI-  Pulp-cavity. 


the  same  manner.  The  bone  becomes  of  greater  circumference  by 
the  deposits  made  by  the  periosteum  externally,  and  the  medul- 
lary canal  is  made  larger  by  the  absorption  of  a  portion  of  its  walls. 
In  the  repair  of  bones,  as  after  fractures,  the  periosteum  performs 

the  same  office  as   in 

"\  the  original  formation 

\  of  bone. 

\  Dentin. — Thecon- 

\  sideration  of  this  sub- 

/\         \  stance  calls   for  a  de- 

scription of  the  teeth, 
of  which  it  forms  an 
important  part. 

A  tooth  (Fig.  40)  is 
divided  anatomically 
into  the  crown,  the  vis- 
ible portion,  which  pro- 
jects above  the  gum ; 
the  root,  the  portion 
out  of  sight  within  the 
alveolus  or  socket ;  and 
the  neck,  the  constricted 
portion  joining  the 
crown  and  the  root. 
In  the  center  of  the 
crown  and  extending 
into  the  roots  is  the 
pulp-chamber,  the 
openings  of  which,  at 
the  tip  of  the  roots, 
are  apical  foramina, 
through  which  pass 
b  1  o  o  d-v  e  s  s  e  1  s  and 
nerves  into  the  pulp- 
chamber,  which  con- 
tains dental  pulp. 
This  latter  is  com- 
posed of  a  gelatinous 
connective  tissue  with 
branched  cells,  to- 
gether with  the  blood- 
vessels and  nerves  just 
mentioned ;  lymphatic  vessels  are  absent.  Some  of  the  cells 
are  in  contact  with  the  dentin  of  the  tooth,  and  having  been 
concerned  in  its  formation  are  called  dentin-forming  cells  or 
odontoblasts. 

The  solid  part  of  a  tooth,  excluding  the  pulp-chamber  and  its 


FIG.  40.— Scheme  of  a  longitudinal  section 
through  a  human  tooth ;  in  the  enamel  are  seen 
the  "lines  of  Retzius"  (Bohm  and  Davidoif). 


DENTIN. 


51 


contents,  is  made  up  of  dentin  or  ivory,  enamel,  and  cement  or 
crusta  petrosa. 

Dentin. — The  main  portion  of  a  tooth  is  composed  of  dentin, 
which  forms  the  walls  of  the  pulp-chamber.  It  bears  some  resem- 
blance to  bone,  though  the  Haversian  canals  and  lacunae,  which 
characterize  the  latter,  are  not  present ;  it  is,  however,  regarded 
as  modified  bone.  Chemically  it  consists  of  10  per  cent,  water 
and  90  per  cent,  solids,  of  which  latter  27.70  per  cent,  is  organic, 
collagen  and  elastin,  and  72.30  per  cent,  inorganic.  Of  this, 
calcium  carbonate  and  phosphate  form  72  per  cent.,  and  magne- 
sium phosphate  and  calcium  fluorid  the  rest. 

Microscopically,  dentin  is  made  up  of  dentinal  tubuli,  hollow 
tubes,  which  present  a  wavy  appearance,  between  which  is  inter- 
tubular  tissue.  In  general,  the  tubules  are  parallel  with  one 


Cementum.  < 


Dentin. 


FIG.  41. — Cross-section  of  human  tooth,  showing  cement  and  dentin ;  X  212 
(Bohm  and  Davidoff ).  At  a  are  seen  small  interglobular  spaces  (Tomes'  granular 
layer). 

another,  although  in  the  upper  part  of  the  crown  they  are 
arranged  vertically,  while  in  the  neck  and  root  they  are  oblique. 
They  extend  from  the  enamel  and  cement  to  the  pulp-chamber, 
into  which  they  open,  and  from  the  odontoblasts  of  which  they 
receive  processes ;  the  dentin  thus  resembling  bone  in  which  bone- 
corpuscles  send  processes  into  the  canaliculi.  At  the  ends,  which 
open  into  the  pulp-chamber,  the  tubules  are  unbranched,  but  as« 
they  extend  toward  the  enamel  and  cement  they  divide  dicho- 
tomously — i.  e.,  into  two  branches,  each  of  which  again  divides 
in  the  same  manner.  They  terminate  beneath  the  enamel  and 
cement  in  irregular  communicating  spaces,  interglobular  spaces 
or  the  granular  layer. 

The   intertubular   tissue  contains  the  greater  portion   of  the 
inorganic  constituents  of  the  dentin. 


FIG.  43. 


v'&«a*S8K:p 


Fio.  42. 


FIG.  44. 


FIG.  45. 


FIGS.  42-45.— Four  stages  in  the  development  of  a  tooth  in  a  sheep  embryo 
(from  the  lower  jaw)  (Bohm  and  Davidoff).  FIG.  42,  anlage  of  the  enamel-germ 
connected  with  the  oral  epithelium  by  the  enamel-edge ;  FIG.  43,  first  trace  of  the 
dentinal  papilla  ;  FIG.  44,  advanced  stage  with  larger  papilla  and  differentiating 
enamel-pulp;  FIG.  45,  budding  from  the  enamel-edge  of  the  anlage  of  the  enamel- 
germ,  which  later  goes  to  form  the  enamel  of  a  permanent  tooth  ;  at  the  periphery 
of  the  papilla  the  odontoblasts  are  beginning  to  differentiate.  FIGS.  42,  43,  and  44, 
X  110;  FIG.  45,  X  40.  a,  a,  a.  a,  Epithelium  of  the  oral  cavity;  6,  6,  6,  6,  its  basal 
layer ;  c,  c,  c,  the  superficial  cells  of  the  enamel-organ ;  d,  d,  d,  d,  enamel-pulp  ; 
p,  p,  p,  dentinal  papilla;  -s,  a,  enamel-forming  elements  (enamel-cells);  o,  odonto- 
blasts; 8,  enamel-germ  of  the  permanent  tooth;  r,  part  of  the  enamel-edge  of  a 
temporary  tooth  ;  u,  surrounding  connective  tissue. 


DENTIN. 


53 


Enamel. — This  covers  the  crown  and  extends  to  the  root.  It  is 
the  hardest  part  of  a  tooth — indeed,  it  is  the  hardest  tissue  in  the 
human  body — and  protects  the  softer  and  more  sensitive  portion 
beneath  in  the  process  of  mastication  or  chewing.  It  is  made  up 
of  elongated  hexagonal  prisms,  enamel-prisms,  which  are  placed 
at  right  angles  to  the  dentin  (Fig.  46). 

Chemical  analyses  of  enamel  vary  to  a  considerable  extent. 
Hoppe-Seyler  gives  the  following :  Calcium  carbonate  and  phos- 
phate, 96  per  cent. ;  magnesium  phosphate,  1  per  cent. ;  and 
organic  substances,  3  per  cent.  Other  chemists  state  the  amount 
of  organic  matter  to  be  from  2  to  10  per  cent. ;  but  the  most  recent 


-  Enamel. 


-  Branching  of  the 
dentinal  tubules. 


—  Dentinal  tubules. 


Interglobular    J 
space. 

FIG.  46.— A  portion  of  a  ground  tooth  from  man,  showing  enamel  and  dentin ; 
X  170  (Bohin  and  Davidoff). 

analyses  seem  to  show  that  the  organic  matter  present  in  the 
enamel  of  a  fully  formed  tooth  is  too  minute  to  be  weighed. 

Cement  or  Crusta  Petrosa. — At  the  point  where  the  enamel 
ends  the  cement  begins,  and  forms  a  covering  of  the  dentin  as 
far  as  the  tip  of  the  root.  It  is  both  structurally  and  chemically 
identical  with  bone,  possessing  both  lacunae  and  canaliculi.  The 
presence  of  Haversian  canals  is  claimed  by  some  histologists,  es- 
pecially in  the  thicker  portions ;  while  others  deny  it  in  normal 
teeth.  Like  bone,  the  cement  is  covered  with  periosteum,  which 


54 


CONNECTIVE  TISSUE. 


lines  the  alveolus  and -holds  the  tooth  in  its  place.     It  is  here 
called  pericementum. 

Development  of  Teeth  (Figs.  42-45).— About  the  seventh  week 
of  fetal  life  the  germinal  epithelium  which  covers  the  mucous  mem- 
brane of  the  gums  of  the  embryo,  grows  so  as  to  form  an  elevated 
ridge,  the  maxillary  rampart.  A  similar  growth  occurs  downward 
into  the  tissue  of  the  mucous  membrane,  forming  the  common 
dental  germ  or  dental  lamina.  From  this  lamina  ten  cellular  proc- 
esses, the  special  dental  germs,  are  given  off  in  each  jaw,  corre- 
sponding to  the  number  of  teeth.  Each  special  germ  becomes 


21  —Enamel-cells. 


Mi 


r«F  ""Odontoblasts. 


FIG.  47.— A  portion  of  a  cross-section  through  a  developing  tooth  (later  stage 
than  in  Fig.  45) ;  X  720  (Bohm  and  Davidoff).  The  den  tin  is  formed,  but  has 
become  homogeneous  from  calcification.  Bleu  de  Lyon  differentiates  it  into  zones 
(a  and  6).  At  c  is  seen  the  intimate  relationship  of  the  odontoblasts  to  the  tissue 
of  the  dental  pulp. 

flask -shaped,  and  later  flattened,  and  still  later  indented  on  its 
under  side.  The  special  germ  becomes  the  enamel-organ  of  the 
future  tooth,  as  from  it  the  enamel  is  produced.  From  the  corium 
of  the  mucous  membrane  grows  a  vascular  papilla,  the  dental 
papilla,  which,  as  it  grows,  increases  the  indentation  of  the  special 
germ  and  is  covered  by  it.  This  papilla  becomes  the  dentin  and 
pulp  of  the  tooth,  the  odontoblasts  which  cover  it  forming  the 
dentin  and  the  other  portion  the  pulp.  From  the  tissue  which 
produces  the  papilla  a  vascular  sac,  the  dental  sac,  is  formed, 
which  surrounds  the  special  germ  and  its  papilla.  The  dental  sac 
and  all  the  structures  within  it  constitute  the  dental  follicle. 


DENTIN.  55 

The  epithelial  cells  of  the  special  dental  germ  become  changed 
into  three  kinds  of  cells :  (1)  Columnar  cells,  adamantoblasts  or 
ameloblasts.  These  are  the  deepest  layer  next  the  papilla,  and 
therefore  next  the  future  dentin.  The  adamantoblasts  form  the 
enamel-prisms  (Fig.  46),  at  first  fibrous  in  character,  later  becoming 
calcified.  (2)  The  outer  cells,  those  adjoining  the  dental  sac,  be- 
come arranged  into  a  single  layer  of  cubical  epithelium.  Between 
the  two  the  cells  form  a  spongy  network  of  (3)  branching  cells, 
whose  processes  communicate,  forming  the  stellate  reticulum  or 
enamel-jelly  or  enamel-pulp.  The  name  enamel-organ  is  now 
applied  to  this  structure. 

The  cement,  which,  as  already  stated,  is  identical  with  bone, 
is  formed  by  the  dental  sac,  whose  internal  tissue  is  in  all  respects 
the  same  as  the  osteogenetic  layer  of  periosteum.  The  outer  layer 
of  this  sac  is  the  dental  periosteum. 

The  above  description  is  that  of  the  development  or  formation 
of  the  temporary  or  milk-teeth  (p.  56).  The  permanent  teeth  are 
formed  in  the  same  manner.  The  process  from  which  each  of 
these  latter  is  developed  is  an  offshoot  of  the  special  dental  germ, 
which  produces  a  temporary  tooth,  and  this  offshoot  undergoes  the 
same  changes.  The  milk-teeth  are  shed  by  the  action  of  the 
osteoclasts  of  the  dental  periosteum,  here  called  odontoclasts,  which 
cause  absorption  of  the  roots  of  these  teeth. 

While  there  are  but  ten  temporary  teeth  in  each  jaw,  there  are, 
on  the  other  hand,  sixteen  permanent  ones,  or  six  more  ;  the  perma- 
nent molars,  three  on  each  side  of  the  jaw,  the  first  and  secondmolarsy 
and  the  wisdom-teeth.  These  arise  from  a  backward  extension  of 
the  dental  germ,  for  which  additional  special  germs  are  developed. 

The  eruption  or  cutting  of  the  teeth  is  due  to  the  absorption  of 
the  gum  about  them  by  the  pressure  of  the  growing  teeth. 

The  alveoli  or  sockets  are  formed  by  the  ossification  of  the 
tissue  between  the  dental  sacs. 

The  ten  teeth  which  replace  the  ten  temporary  are  called  succes- 
sional  permanent  teeth  ;  the  other  six,  superadded  permanent  teeth. 
The  molars  of  the  temporary  set  are  replaced  by  the  pre molars 
or  bicuspids  of  the  permanent  set,  while  the  superadded  teeth  are 
the  molars  of  the  permanent  set,  and  have  no  representatives  in 
the  temporary  set. 

While  the  formation  of  the  milk-teeth  begins  at  about  the 
seventh  week  of  fetal  life,  that  of  the  successional  permanent 
teeth  commences  at  about  the  sixteenth  week,  the  second  molars 
at  the  third  month,  and  the  wisdom  teeth  at  the  third  year. 

Temporary,  Milk-,  or  Deciduous  Teeth.— The  first  set  of  teeth, 
ten  in  number  in  each  jaw,  twenty  in  all,  constitute  the  temporary, 
milk-,  or  deciduous  teeth.  Four  of  these  are  incisors,  two  canines, 
and  four  molars.  The  following  table  gives  their  arrangement 
and  approximate  time  of  eruption  or  cutting. 


56  MUSCULAR  TISSUE. 

TEMPORARY  TEETH. 

Arrangement  and  Time  of  Eruption. 

One-half  only  of  each  jaw  is  represented,  the  arrangement  and  time  of  erup- 
tion being  the  same  in  the  corresponding  halves. 

Molars.  Canine.  Incisor.  Middle  line 

Second.        First.  Lateral.      Central.       of  jaw. 

Upper  jaw 1  1  1  1 

Time  of  eruption  ) 

in  months  after  I  .  20-24         15-21         16-20         15-21  8-10 

birth     .    .    .    .  J 

Lower  jaw 1  1  1  1 

Time  of  eruption  ) 

in  months  after  \  .  20-24  12  16-20         15-21  6-9 

birth     .    .    .    .  J 

Permanent  Teeth. — The  second  or  permanent  set  consists  of 
thirty-two  teeth,  sixteen  in  each  jaw.  The  third  molars  or  wis- 
dom teeth  do  not  always  appear.  The  following  table  gives  the 
arrangement  of  these  teeth  and  the  approximate  time  of  their 
eruption  : 

PERMANENT  TEETH. 

Arrangement  and  Time  of  Eruption. 

One-half  only  of  the  jaw  is  represented,  the  other  half  corresponding  in  all 
particulars ;  and  as  the  time  of  eruption  of  the  permanent  teeth  of  the  lower 
jaw  differs  from  that  of  the  upper  only  in  that  it  precedes  it  slightly,  the  upper 
jaw  is  alone  represented. 

Bicuspid  or 

Third  or       Molar.  1'remolar.  Canine.     Incisor.      Middle  line 

Wisdom.  Second.  First.  Second.  First.        Lateral.  Central,    of  jaw. 

Upper  jaw  ....      1  1          1  1          111  1  | 

Time  of  eruption  ) 

in    years    after  1 17-25       12         6          10          9        11        8  7 

birth     .    .    .    .  J 

MUSCULAR  TISSUE. 

The  muscular  tissue  of  the  human  body  is  of  two  kinds,  volun- 
tary and  involuntary r,  both  being  possessed  of  contractility  or  the 
power  to  shorten. 

Voluntary  Muscle  (Fig.  49).— This  is  composed  of  fibers 
having  a  length  of  2.5  cm.  or  more,  and  a  diameter  of  0.05  mm., 
enclosed  in  a  sheath,  the  sarcolemma  (Fig.  48).  The  material 
possessed  of  contractile  power,  contractile  substance,  when  viewed 
under  the  microscope  presents  the  appearance  of  alternating  dark 
and  light  stripes,  strive,  crossing  it,  giving  to  this  variety  the  name 
of  striated  muscle.  These  striae  are  not  superficial  markings,  but 
are  in  reality  the  edges  of  dark  and  light  disks  (Fig.  49).  At  the 
boundaries  of  the  light  striae  are  seen  rows  of  granules,  and  run- 
ning through  the  dark  striae  lines  connecting  the  granules.  These 
lines  mark  longitudinally  the  subdivisions  of  the  muscle,  which 


VOLUNTARY  MUSCLE. 


57 


are  called  muscle-columns,  sarcostyles,  or  fibrils.  When  stained  with 
chlorid  of  gold  transverse  lines  are  also  seen  uniting  the  granules, 
the  whole  arrangement  of  lines  presenting  a  reticular  appearance, 


FIG.  43.—  Striated  muscle-fiber  of  frog,  showing  sarcoleinma  (Huber). 

which,  however,  Schafer  regards  as  in  reality  not  a  network,  but 
only  the  optical  expression  of  the  interstitial  substance  between 
the  muscle-columns,  and  which  is  called  sarcoplasm. 

If  a  muscle-fiber  is  examined  in  cross-section,  it  is  found  to  be 
divided  into  angular  areas,  Cohnheim's  areas  (Fig.  51).    These  are 


FIG.  49.— Voluntary  muscle  (Leroy).  A,  Three  voluntary  fibers  in  long  sections: 
a,  three  voluntary  muscle-fibers;  b,  nuclei  of  same;  c,  fibrous  tissue  between  the 
fibers  (endomysium) ;  d,  fibers  separated  into  sarcostyles.  B,  Fiber  (diagrammatic): 
a,  dark  band ;  6,  light  band ;  c,  median  line  of  Hensen ;  d,  membrane  of  Krause ; 
e,  sarcolemma;  /,  nucleus.  C:  a,  Light  band  ;  b,  dark  band;  c,  contracting  ele- 
ments ;  d,  row  of  dots  composing  the  membrane  of  Krause ;  e,  slight  narrowing  of 
contracting  element  aiding  in  production  of  median  line  of  Hensen. 

the  cross-sections  of  the  muscle-columns  or  sarcostyles,  between 
which  is  the  sarcoplasm. 

Hensen's  line  is  a  line  crossing  a  muscle-fiber  in  the  middle  of 


58 


MUSCULAR  TISSUE. 


a  dark  stripe,  while  Dobie's  line  crosses  each  light  stripe.  This 
latter  is  regarded  by  Schafer  as  not  an  actual  structure,  but  an 
effect  produced  by  the  transmitted  light.  One  authority,  Hay- 
croft,  regards  the  striated  appearance  of  muscle  as  a  refractive 
effect  simply ;  but  the  evidence  of  this  is  not  convincing,  and  the 
difference  in  reaction  to  stain  ing-agents  seems  to  prove  that  the 
light  and  dark  stripes  of  muscle-fibers  are  different  structures. 


*Sarcoplasm. 


FIG.  50.— Diagram  of  the  struct- 
ure of  the  fibrils  of  a  striated 
muscle-fiber ;  the  light  spaces  be- 
tween the  fibrils  may  represent 
the  sarcoplasin  (Huber). 


Sarcoplasm. 
Fibrils. 
-Sarcolemma. 


FIG.  51. — Transverse  section  through  stri- 
ated muscle-fibers  of  a  rabbit  (Bohm  and 
Davidoff).  1  and  3,  from  a  muscle  of  the 
lower  extremity;  2,  from  a  lingual  muscle; 
X900.  In  2,  Cohnheim's  fields  are  distinct; 
in  1,  less  clearly  shown ;  in  3,  the  muscle- 
fibrils  are  more  evenly  distributed. 


Nuclei  are  to  be  seen  under  the  sarcolemma  of  the  muscular 
tissue  presenting  the  usual  appearance  of  cell-nuclei,  often  with 
spiral  chromoplasm. 

Endomysium  is  the  areolar  tissue  between  the  individual  fibers, 
which  are  bound  together  by  connective  tissue,  perimysium,  into 
bundles,  fasciculi;  these  in  turn,  united  by  the  perimysium,  con- 
stitute what  is  commonly  called  a  muscle,  whose  investment  or 
sheath  is  the  epimysium. 

The  muscles  of  insects  are  characterized  by  broad  stripes  whose 


VOLUNTARY  MUSCLE.  59 

structure  is  very  distinct,  and  the  following  description  from 
Schafer  is  very  instructive.  He  says : 

"  The  wing-muscles  of  insects  are  easily  broken  up  into  sarco- 
styles  (fibrils),  which  also  show  alternate  dark  and  light  striae. 

"  The  sarcostyles  are  subdivided  at  regular  intervals  by  thin 
transverse  disks  (membranes  of  Krause)  into  successive  portions, 
which  may  be  termed  sarcomeres.  Each  sarcomere  is  occupied  by 
a  portion  of  the  dark  stria  of  the  whole  fiber  (sarcous  element) : 
the  sarcous  element  is  really  double,  and  in  the  stretched  fiber 
separates  into  two  at  the  line  of  Hensen.  At  either  end  of  the 
sarcous  element  is  a  clear  interval  separating  it  from  the  mem- 
brane of  Krause ;  this  clear  interval  is  more  evident  the  more  the 
sarcostyle  is  extended,  but  diminishes  to  complete  disappearance 
in  the  contracted  muscle.  The  cause  of  this  is  to  be  found  in  the 


Nucleus. 

Muscle- 
substance. 
Sarcolemma. 


FIG.  52. — Cross-section  of  striated  muscle-fibers :  1,  of  man ;  2,  of  the  frog ;  the 
relations  of  the  nuclei  to  the  muscle-substance  and  sarcolemma  are  clearly  visible ; 
X  670  (Bohm  and  Davidoff ). 

structure  of  the  sarcous  element.  Each  sarcous  element  is  per- 
vaded with  longitudinal  canals  or  pores,  which  are  open  in  the 
direction  of  Krause' s  membranes,  but  closed  at  the  middle  of  the 
sarcous  element.  In  the  contracted  or  retracted  muscle  the  clear 
part  of  the  muscle-substance  has  passed  into  these  pores,  and  has 
therefore  disappeared  from  view,  but  swells  up  the  sarcous  element 
and  shortens  the  sarcomere  in  the  extended  muscle ;  on  the  other 
hand,  the  clear  part  has  passed  out  from  the  pores  of  the  sarcous 
element,  and  now  lies  between  this  and  the  membrane  of  Krause, 
the  sarcomere  being  thereby  lengthened  and  narrowed.  The  sar- 
cous element  does  not  lie  free  in  the  middle  of  the  sarcomere,  but 
is  attached  laterally  to  a  fine  enclosing  envelope,  and  at  either  end 
to  Krause's  membrane  by  very  fine  lines,  which  may  represent 
fine  septa  running  through  the  clear  substance." 

Schafer  regards  the  sarcomere  as  similar  to  the  protoplasm  of 
an  ameboid  cell,  the  substance  of  the  sarcous  element  being  repre- 


60 


MUSCULAR  TISSUE. 


sented  by  the  spongioplasm,  and  the  clear  substance  by  the  hyalo- 
plasm. When  stimulated, 
the  clear  substance  passes 
into  the  pores  as  the  hyalo- 
plasm does  into  the  spongio- 
plasm, thus  producing  con- 
traction ;  and  in  the  absence 


FIG.  53. — Diagrams  of  the  transverse  stria- 
tion  in  the  muscle  of  an  arthropod ;  to  the 
right  with  the  objective  above ;  to  the  left 
with  the  objective  below  its  normal  focal 
distance  (after  Rollet,  85) :  Q,  transverse 
disk;  h,  median  disk  (Hensen);  E,  terminal 
disk  (Merkel) ;  N,  accessory  disk  (Engel- 
mann) ;  J,  isotropic  substance  (Bohm  and 
David  off). 


FIG.  54. — Cardiac  muscle, 
semidiagrammatic:  a,  nu- 
cleus; b,  branch  of  fibers;  c, 
cross-striation . 


of  stimulation  it  passes  out,  as  in  the  case  of  the  ameba,  causing 
in  it  the  formation  of  pseudopodia,  and  in  the  muscle  its  extension. 


-  Nucleus 


Contractile 
substance. 


Contractile 

substance. 
-Nucleus. 


FIG.  55.  FIG.  &>. 

Longitudinal  and  cross-section  of  muscle-fibers  from  the  human  myocardium, 
hardened  in  alcohol ;  x640.  The  muscle-cells  in  the  longitudinal  section  are  not 
sharply  defined,  and  appear  as  polynuclear  fibers  blending  with  one  another :  between 
them  lie,  here  and  there,  connective-tissue  nuclei  (Bohm  and  Davidoff). 


INVOLUNTARY  MUSCLE. 


61 


Nucleus. 
-  Protoplasm. 


He  calls  attention  to  the  similarity  of  the  movements  of  the  ameba, 
muscle,  and  cilia. 

Muscles  are  well  supplied  with  blood-vessels,  which  run 
lengthwise  of  the  muscle  with  transverse  branches ;  they  do  not 
penetrate  the  sarcolemma.  The  motor  nerves  of  striated  muscle 
terminate  in  motor  end-organs,  and  the  sensory  nerves  in  muscle- 
spindles,  which  are  further  referred  to  in  the  discussion  of  Nerve- 
endings  (p.  64).  Besides  the  muscle- 
fibers,  muscles  contain  connective  tissue 
with  some  fat. 

Striated  muscle  is  found  in  all  the 
muscles  of  the  body  which  are  attached 
to  bone,  and  is  sometimes  described  un- 
der the  name  skeletal  muscle.  Although 
this  variety  is  said  to  be  voluntary,  it  is 
not  in  all  places  under  control  of  the 
will,  as,  for  instance,  in  the  pharynx, 
esophagus,  and  the  internal  ear. 

Development  of  Striated  Muscular 
Tissue. — Embryonic  cells  of  the  meso- 
blast  become  elongated,  and  the  nuclei 
form  long  fibers,  which  later  become 
striated ;  some  of  the  nuclei  remain 
beneath  the  sarcolemma  as  the  nuclei 
of  the  muscle. 

Cardiac  Muscle  (F\g.  54). — The  mus- 
cle of  which  the  heart  consists  differs 
from  that  just  described  in  having  its 
strise  less  marked,  in  being  without  sar- 
colemma, and  in  the  fact  that  its  fibers 
are  short,  each  possessing  a  nucleus,  and 
that  they  branch  and  join  the  fiber- 
cells  contiguous  to  them. 

The  nerves  supplying  cardiac  muscle 
end  in  plexuses  or  networks. 

Involuntary  Muscle  (Fig.  57). — 
This  is  also  called  plain  and  non-striated. 
It  consists  of  flat,  fusiform  cells,  contrac- 
tile fiber-cells,  having  lengths  varying 
considerably,  each  possessing  a  nucleus  and  one  or  two  nucleoli, 
and  having  longitudinal  striae.  The  cells  are  joined  together  by 
means  of  an  intercellular  material. 

Involuntary  muscular  tissue  is  widely  disseminated  over  the 
body  ;  it  is  found  in  the  following  locations  :  esophagus,  muscular 
and  mucous  coats  of  the  alimentary  canal,  bladder,  ureter,  uterus, 
Fallopian  tubes,  spleen,  ciliary  muscle,  iris,  ducts  of  glands,  arte- 


FIG.  57. — Smooth  muscle- 
cells  from  the  intestine  of  a 
cat :  in  1,  isolated  ;  in  2  and  3, 
in  cross-section ;  X  300.  At  a 
the  cell  is  cut  in  the  plane  of 
the  nucleus ;  at  c,  in  the  neigh- 
borhood of  the  pointed  end. 
In  3  (from  Barfurth)  is  seen 
the  manner  in  which  neigh- 
boring cells  are  joined  to  one 
another  by  intercellular  bridges 
(Bohm  and  Davidoff). 


62  MUSCULAR  TISSUE. 

ries,  veins,  lymphatics,  sweat-glands  connected  with  hair-follicles, 
scrotum,  and  areola  of  the  nipple  of  the  breast. 

The  nerves  of  involuntary  muscle  end  in  plexuses  or  networks, 
as  in  the  cardiac  muscle. 

Development  of  Involuntary  Muscular  Tissue. — The  contractile 
fiber-cells  which  compose  this  tissue  are  formed  from  cells  of  the 
mesoblast,  which  elongate,  the  nuclei  also  elongating.  The 
muscular  tissue  of  the  sweat-glands  is  formed  from  the  epiblast. 
When  new  muscular  tissue  of  the  plain  variety  is  formed,  as  when 
the  uterus  enlarges  in  pregnancy,  growing  from  an  organ  weighing 
from  30  to  40  grams  to  one  weighing  from  900  to  1100  grams, 
this  is  accomplished  by  an  increase  in  the  size  of  the  original 
fibers,  and  by  the  formation  of  new  fibers  from  small  cells  which 
lie  between  the  original  ones.  In  the  process  of  involution,  that 
process  by  which  the  uterus  returns  to  its  original  size,  the  fibers 
become  fatty  and  are  absorbed. 

Chemical  Composition  of  Striated  Muscular  Tissue. — The  sarco- 
lemma  resembles  elastin.  When  the  contractile  substance  is 
pressed,  a  fluid  is  expressed,  the  muscle-plasma,  which  coagulates, 
the  clot  being  myosin.  A  similar  change  takes  place  after  death, 
producing  rigor  mortis  or  cadaveric  rigidity.  During  life  muscular 
tissue  has  an  alkaline  reaction ;  while  after  death,  owing  par- 
tially, at  least,  to  the  formation  of  sarcolactic  acid,  it  becomes  acid. 
This  also  occurs  after  the  muscles  have  been  very  active. 

PERCENTAGE  COMPOSITION  OF  HUMAN  MUSCLES. 

Water 73.5 

Proteids,  including  the  sarcolemma,  proteids  of  connective 

tissue,  vessels,  and  pigments 18.02 

Gelatin 1.99 

Fat 2.27 

Extractives 0.22 

Inorganic  salts 3.12 

The  proteids  in  muscle-plasma  are  three  in  number:  1.  Para- 
myosinogen,  which  coagulates  at  47°-50°  C.,  constituting  17  to 
22  per  cent,  of  the  total  proteid  ;  2.  Myosinogen  or  Myogen,  coag- 
ulating at  56°  C.,  77  to  83  per  cent. ;  and  traces  of  an  albumin, 
Myo-albumin.  Both  paramyosinogen  and  myosinogen  enter  into 
the  clot  which  forms  when  the  plasma  coagulates.  This  clot  is 
called  myogen-fibrin  or  myosin-fibrin. 

The  extractives  are  very  numerous,  creatin,  creatinin,  xan- 
thin,  hypoxanthin,  earn  in,  carnic  acid,  uric  acid,  tannin,  and 
inosinic  acid,  all  containing  nitrogen  and  fats,  glycogen,  inosit, 
dextrose,  and  sarcolactic  acid.  This  acid  is  attributed  by  some 
authorities  to  the  glycogen,  while  others  trace  it  to  the  proteids. 
The  presence  of  urea  in  mammalian  muscular  tissue  is  still  a 
matter  of  dispute.  Muscular  tissue  always  contains  fat,  and  there 
is  excellent  authority  for  believing  that,  while  some  of  this  comes 


NERVE-FIBERS. 


63 


from  the  adipose  tissue  which  cannot  be  separated  from  the  true 
muscular  tissue,  fat  is  also  a  constituent  part  of  muscle-plasma. 

The  coloring-matter  of  the  red  muscle  is  myohematin,  which  is 
probably  produced  from  the  hemoglobin  of  the  blood. 

The  inorganic  salts  are  principally  those  of  potassium,  the  most 
abundant  being  potassium  phosphate. 

Composition  of  the  Cardiac  Muscle. — This  variety  of  muscular 
tissue  contains  paramyosinogen  and  myosiuogen,  and  undergoes 
cadaveric  rigidity. 

Composition  of  Involuntary  Muscular  Tissue. — Cadaveric  rigidity 
has  been  observed  in  the  stomach  and  uterus ;  and  from  plain 
muscular  tissue  a  proteid  has  been  obtained  which  resembles 
myosinogen. 

NERVOUS  TISSUE. 

The  nervous  tissue  of  the  body  is  made  up  of  nerve-fibers, 
nerve-cells,  and  neuroglia. 

Nerve-fibers  (Fig.  58). — This  kind  of  nervous  tissue  is  also 
called  fibrous  and  white  nervous  matter. 
Fibrous  nervous  matter  should  not  be 
confounded  with  fibrous  connective  tis- 
sue ;  the  term  "  fibrous"  simply  implies 
that  the  nervous  substance  is  arranged 
in  fibers. 

Nerve-fibers  are  medullated  and  non- 
medullated. 

Medullated  Nerve-fibers  (Fig.  58)  are 


Medullary 

sheath. 


Fibrils  of  axial 
cord. 


--  Neurilemma. 


Segment  of 
Lantermann. 


Axis-cylin- 
der. 


FIG.  58.  FIG.  59. 

FIG.  58. — Longitudinal  section  through  a  nerve-fiber  from  the  sciatic  nerve  of  a 
frog  ;  X  830  (Bohm  and  Davidoff ). 

FIG.  59. — Medullate  nerve-fiber  from  sciatic  nerve  of  a  frog;  in  two  places  the 
medullary  sheath  has  been  pulled  away  by  teasing,  showing  the  "naked  axis- 
cylinder";  X212  (Bohm  and  Davidoff). 


64 


NERVOUS  TISSUE. 


characterized  by  possessing  a  medullary  sheath  or  white  substance 
of  Schivann,  which  gives  the  white  color  to  the  nerve-fiber.  This 
is  a  protective  covering  to  the  essential  part  of  a  nerve,  the  axis- 
cylinder.  The  space  inside  the  medullary  sheath  is  the  axial  space, 
which  is  filled  by  the  axial  cord.  This  consists  of  axis-fibrils  em- 
bedded in  the  neuroplasm,  a  material  of  semi-fluid  consistency, 
both  fibrils  and  neuroplasm  being  covered  by  a  delicate  mem- 
brane, the  axolemma.  When  nerve-fibers  have  been  prepared  for 
microscopic  examination  the  axial  cord  changes  its  appearance  by 
the  coagulation  of  the  neuroplasm,  and  the  altered  cord  is  what  is 
commonly  called  the  axis-cylinder.  The  primitive  sheath,  nucleated 
sheath  of  Schwann,  or  neurilemma,  is  a  membrane  which  encloses 
the  white  substance  of  the  nerves,  except- 
ing those  within  the  nerve-center.  Neuri- 
lemma (also  written  neurolemma)  is  a  term 
formerly  applied  to  what  is  now  called peri- 
neurium. 

The  medullary  sheath  is  not  continuous ; 
at  regular  intervals  it  is  absent,  and  only 
the  primitive  sheath  and  axis-cylinder  are 
present.  This  gives  to  the  nerve  the  ap- 
pearance of  constrictions,  known  also  as 
the  nodes  of  Ranvier.  The  portion  of 
nerve  between  these  constrictions  is  an 
internode,  in  the  middle  of  which  is  a  nu- 
cleus. 

Medullated  fibers  make  up  the  white 
part  of  the  brain  and  spinal  cord,  and  the 
nerves  that  have  their  origin  in  these  struct- 
ures, the  cerebrospinal  nerves.    In  size  they 
vary  from  2  p  to  19  p..     This  variety  never 
branches  except  near  the  termination. 
Nonmedullated  Nerve-fibers  (Fig.  60). — These  are  also  known  as 
gray,  gelatinous,  and  fibers  of  Remak.     These  have  no  white  sub- 
stance, but  are  composed  of  fibrillae,  which  are  probably  enclosed 
in  a  sheath,  the  neurilemma,  in  which  are  nuclei. 

Nonmedullated  fibers,  unlike  those  that  are  medullated,  fre- 
quently branch. 

Nerve-fibers  are  associated  together  in  bundles,  funiculi  (Fig. 
61),  each  of  which  bundles  is  enclosed  in  a  sheath  of  connective 
tissue,  perineurium.  The  funiculi  are  surrounded  by  a  similar 
sheath,  the  epineurium,  which  binds  them  together  and  in  which 
are  the  blood-vessels,  lymphatics,  and  nerves  of  the  nerves,  the 
last  being  the  nervi  nervorum.  Within  the  funiculi  is  connective 
tissue,  embedded  in  which  are  the  nerve-fibers. 

Modes  of  Termination  of  Nerve-fibers. — The  nerves  which 
supply  striated  muscle  subdivide  near  their  ends,  and  one  of  the 


-  Nucleus. 


FIG.  60. — Remak' s  fibers 
(nonmedullated  fibers)  from 
the  pneutnogastric  nerve  of 
a  rabbit ;  X  360  (Bohm  and 
Davidoff). 


NERVE-FIBERS.  65 

branches  goes  to  a  muscular  fiber.  Its  primitive  sheath  is  con- 
tinuous with  the  sarcolemma,  and  the  medullary  sheath  terminates. 
The  axis-cylinder  breaks  up  into  fine  ramifications,  which  are  em- 
bedded in  granular  nucleated  protoplasm  ;  this  is  a  motor  end-organ 
or  end-plate  (Figs.  62-65). 

In  involuntary  muscle  the  nerve-fibers  end  in  plexuses,  from 
which  fine  branches  pass  to  the  contractile  fiber-cells. 

Nerve-fibers  also  end  in  special  organs,  of  which  there  are 
various  kinds :  End-bulbs  of  Krause,  tactile  corpuscles,  Pacinian 
corpuscles,  organs  of  Golgi,  and  muscle-spindles. 

End-bulbs  (Fig.  67). — An  end-bulb  consists  of  a  cylindrical, 
oblong,  or  spheroidal  body  formed  from  the  connective- tissue 
sheath  of  a  medullated  nerve-fiber.  Within  this  is  a  core  with 
many  nucleated  cells,  in  which  the  axis-cylinder  terminates.  End- 


Connective— - 

tissue. 


Fibrils  of  axial    ^  Wm&^ZS&ZMll Wm^?-~  Fibrils, 
cord. 

Medullary 
sheath. 

FIG.  61. — Transverse  section  through  the  sciatic  nerve  of  a  frog ;  X  820;  at  a  and  6 
is  a  diagonal  fissure  between  two  Lantermann  segments ;  as  a  result,  the  medullary 
sheath  here  appears  double  (Bohm  and  Davidoff).  (Compare  Fig.  60.) 

bulbs  are  found  in  the  conjunctiva,  in  the  papillae  of  the  lips  and 
tongue,  the  skin  and  mucous  membrane  of  the  penis,  the  clitoris, 
vagina,  epineurium  of  nerve-trunks,  and  in  tendon. 

In  the  synovial  membrane  of  some  joints,  as  in  the  fingers, 
end-bulbs  also  occur,  and  are  here  called  articular  end-bulbs. 

Tactile  Corpuscles. — These  consist  of  connective  tissue  which 
forms  a  capsule,  from  which  are  given  off  membranous  partitions 
or  septa.  After  winding  around  the  corpuscle  the  axis-cylinder 
enters  it,  and  terminates  in  an  enlargement.  Tactile  corpuscles 
occur  in  the  papillae  of  the  skirt  of  the  hand,  foot,  front  of  the 
forearm,  lips,  and  nipple ;  also  in  the  mucous  membrane  of  the 
tip  of  the  tongue  and  the  conjunctiva  lining  the  eyelids. 

Pacinian  Corpuscles  (Fig.  70). — These  are  also  called  corpuscles 
of  Vater.  Each  corpuscle  consists  of  concentrically  arranged 
layers  of  connective  tissue,  with  nucleated  cells.  A  medullary 


NERVOUS  TISSUE. 


-So-called 
granular 
sole. 


==    1=:^=?=--  -Nerve. 


FIG.  63. 


—  Nerve. 


So-called 

'i granular 

sole. 
I End-brush. 


'Muscle- 
fiber. 


FIGS.  64  and  65. 


So-called 
-    granular 

sole. 
—  End-brush. 


Sarco- 
lemma. 


FIGS.  62-65. — Motor  endings  in  striated  voluntary  muscles. 

FlG.  62,  from  Pseudopus  Pallasii ;  X  160.  FIG.  63,  from  Lacerta  viridis ;  X  160,, 
FIGS.  64  and  65,  from  a  guinea-pig ;  X  700.  FIG.  66,  from  a  hedgehog ;  x  1200. 
As  a  consequence  of  the  treatment  (T.  182,  I)  the  arborescence  is  shrunken  and  in- 
terrupted in  its  continuity.  In  Figs.  62  and  63  the  end-plate  is  considerably  larger 
than  in  Figs.  64  and  65.  In  Fig.  62  it  is  in  connection  with  two  nerve-branches. 
Fig.  66  shows  a  section  through  an  end-plate.  The  latter  is  bounded  externally  by 
a  sharply  defined  line,  which  can  be  traced  along  the  surface  of  the  muscle-fiber. 
This  is  to  be  regarded  as  the  sarcolemma  (Bohm  and  Davidoff). 


NERVE-FIBERS. 


67 


nerve-fiber  enters  at  one  end  and  passes  into  an   interior  space 
which   contains   a   transparent   substance ;    here   only   the   axis- 


FIG.  67. — End-bulb  of  Krause  from 
conjunctiva  of  man  ;  methylene-blue 
stain  (Dogiel). 


FIG.  68.— Cylindric  end-bulb  of  Krause 
from  intermuscular  fibrous  tissue  septum 
of  cat ;  methylene-blue  stain  (Huber). 


cylinder  is  present.     This  terminates  at  the  end  of  the  corpuscles 
in  an  enlargement  or  in  minute  branches,  an  arborization. 

These  corpuscles  exist  in  the  subcutaneous  tissue  of  the  palm 


--  Nucleus  of  lamellae. 

—  End-cell  of  core. 
Lamellae. 

Axis-cylinder  in  core. 

Cubic  cells  of  core. 

-  Termination  of  medul- 
lary sheath. 


Axis-cylinder  of  nerve- 
fiber. 


Medullary  sheath  of 

nerve-fiber. 

Neurilemma  and  sheath 

of  Henle. 
FIG.  69.— Corpuscle  of  Herbst  from  bill  of  duck  ;  x  600  (Bohm  and  Davidoff). 

of  the  hand  and  sole  of  the  foot,  and  in  the  penis.  Observers 
have  also  found  them  in  the  pancreas,  lymphatic  glands,  and 
thyroid. 


68 


NERVOUS  TISSUE. 


FIG.  70. — Pacinian  corpuscles  from  mesorectum  of  kitten:  A,  showing  the  fine 
branches  on  central  nerve-fiber ;  B,  the  network  of  fine  nerve-fibers  about  the  cen- 
tral fiber ;  methylene-blue  preparation  (Sala). 


FIG.  71. — Genital   corpuscle  from  the 
glans  penis  of  man ;  methylene-blue  stain 

(Dogiel). 


FIG.   72. — Meissner's  tactile  corpus- 
cle ;  methylene-blue  stain  (Dogiel). 


NERVE-CELLS. 


69 


Organ  of  Golgi  (Fig.  73). — At  the  point  where  muscles  and 
their  tendons  join,  the  tendon-bundles 
present  an  enlargement,  between  the 
fasciculi  of  which  one,  two,  or  more 
nerve-fibers  enter  to  terminate  in  an 
arborization  which  is  characterized 
by  varicosities.  The  term  "  organ 
of  Golgi "  includes  the  enlargement 
and  the  arborizations. 

Muscle-spindles. — These  are  de- 
scribed under  the  name  neuro-mus- 
cular  spindles.  A  spindle  is  a  fusi- 
form body  having  a  length  of  from 
0.75  mm.  to  4  mm.  Externally  is  a 
sheath  of  connective  tissue  within 
which  is  the  interposed  bundle,  con- 
sisting of  from  ten  to  twelve  muscle- 
fibers,  resembling  embryonic  fibers. 
The  nerve-fibers  distributed  to  these 
spindles  divide,  and  the  axis-cylin- 
ders clasp  the  fibers  by  flattened  ex- 
pansion. None  of  these  spindles  has 
been  found  in  either  the  muscles  of 
the  eye  or  the  tongue.  They  are  con- 
sidered to  be  sensory  nerve-endings  in 
the  muscles. 

Nerve-cells  (Figs.  75-78).— 
This  kind  of  nervous  tissue  is  also 
called  gray,  cineritious,  cellular, 
vesicular,  nervous  matter. 

Nerve-cells  are  of  different  sizes, 
varying  from  4  p.  to  150  /j>.  Their 
shape  also  varies  greatly,  some  being 
ovoid,  while  others  are  very  irregular 
in  outline.  Each  cell  contains  a  large, 
distinct,  and  spheroidal  nucleus,  with 
a  single  nucleolus,  and  fibrillated  pro- 
toplasm. In  the  protoplasm  are  some- 
times angular  granules,  Nissl's  gran- 
ules, which  are  stained  by  methylene- 
blue. 

From  nerve-cells  are  given  off  two 
kinds  of  processes  :  axis-cylinder  pro- 
cesses  or  neuraxe,,  and  protoplasmic 

processes  or  dendrites.      These  are  the      preparation   of  tissue  stained  in 
principal    elements    in    nerve-fibers,     methyiene-blue  (Huber  and  De 

£,,         r  Witt,  Jour,  of  Comp.  A  enrol.,  vol. 

Ine   number   01   these   processes   or     x.). 


70  NERVOUS  TISSUE. 

poles  determines  the  name  of  the  cell :  thus  a  cell  with  one  pole 


*  *  Sfc-' 


m%mm&. 


p 


FIG.  74. — Cross-section  of  neurotendinous  nerve  end-organ  of  rabbit,  from  tissue 
stained  in  methylene-blue :  m,  muscle-fibers ;  t,  tendon  ;  c,  capsule  of  neurotendi- 
nous end-organ  ;  m  n,  medullated  nerve-fiber  (Huber  and  DeWitt,  Jour,  of  Comp. 
Neurol.,  vol.  x..). 

is  unipolar ;  one  with  two  poles,  bipolar ;  and  one  with  three  or 
more,  multipolar. 


Nucleus. 


r , — •  Nucleolus. 

Fibrillar  structure. 

Medullary  sheath. 


FIG.  75. — Bipolar  ganglion-cell  from  the  ganglion  acusticum  of  a  teleost  (longi- 
tudinal section)  ;  the. medullary  sheath  of  the  neuraxis  and  dendrite  is  continued 
over  the  ganglion-cell ;  X  800  (Bohm  and  Davidoff). 

The  process  in  a  so-called  "  unipolar"  cell  is,  in  reality,  two 
processes  which  have  become  united.  Such  cells  occur  in  the 
spinal  ganglia  (Fig.  78). 


NERVE-CELLS. 


71 


Axis-cylinder  Process. — Every  nerve-cell  has  an  axis-cylinder 
process,  which,  in  the  medullated  nerve-fiber,  becomes  the  axis- 
cylinder,  and  in  the  non-medullated  is  the  nerve-fiber  itself.  This 


,.  Dendrite. 


Neuraxis. 


FIG.  76.— A  ganglion-cell  from  anterior  horn  of  the  spinal  cord  of  calf;  teased 
preparation  ;  X  140 ;  by  this  method  only  the  coarsest  ramifications  of  the  dendrites 
are  preserved ;  the  rest  are  torn  off  (Bohm  and  Davidoff ). 

process  is  characterized  by  the  fact  that  it  gives  off  a  few 
side-shoots,  collaterals  in  its  course ;  thus  its  branching  is  very 
limited.  To  this  process  some  histologists  apply  the  term  neuronj 


-Dendrite. 


Neuraxis. 


Neuraxis. 


Dendrite.-" 


FIG.  77. — Motor  neurones  from  the  anterior  horn  of  the  spinal  cord  of  a  newborn 
cat;  chrome-silver  method  (Huber). 

while  others  call  it  neuraxon,  or  axon,  and  reserve  the  term 
"neuron*1  for  the  whole  nerve-unit — that  is,  the  cell  and  all  its 
processes,  for  which  the  term  neurone  is  more  commonly  used. 


72  NERVOUS  TISSUE. 

Cells  which  have  but  one  axis-cylinder  process  are  mononeuric ; 
those  having  two  such  processes  are  dineuric ;  and  trineuric  is 
applied  to  those  having  three.  Most  nerve-cells  are  mononeuric. 
Ganglia. — A  ganglion  is  a  collection  or  group  of  nerve-cells. 
These  occur  upon  the  posterior  roots  of  the  spinal  nerves  (Fig. 
78),  upon  some  of  the  cranial  nerves,  and  in  connection  with  the 
sympathetic  nervous  system.  In  these  structures  the  cells  have 
a  nucleated  sheath  continuous  with  that  of  the  nerve-fibers  con- 
nected with  them.  From  each  cell  in  the  ganglion,  upon  the  roots 
of  the  spinal  cord,  and  among  the  cranial  nerves  is  given  off  but 
one  process,  the  axis-cylinder  process.  Passing  in  a  convoluted 
form  from  the  cell,  this  process,  before  it  leaves  the  ganglion, 
divides  into  two,  one  going  to  the  nerve-center,  the  other  to  the 

periphery.  From  this  descrip- 
tion it  will  be  seen  that  these 
cells  have  no  dendrons. 

In  the  cells  of  the  sympathetic 
ganglion,  besides  the  axis-cylin- 
der process,  there  are  also  sev- 
eral dendrons. 

Protoplasmic  Process. — Unlike 
the  axis-cylinder  process,  this  va- 
riety is  characterized  by  its  fre- 
quent branching.  The  larger 
branches  are  called  dendrons, 

and  the  finer  ones  dendrites. 
FIG.  78.— Ganglion-cell  with  a  pro-  mi      •  i        ,1         ,1  •         T 

cess  dividing  at  a  (T-shaped  process);  I  he  idea   that  the  axiS-cylm- 

from  a  spinal  ganglion   of  the  frog;       Jer    process    alone    COnvevS    lier- 
X230  (Bohm  and  Davidoff).  .  -,  j    ,1     ,    .1        i 

vous  impulses,  and  that  the  den- 
drons and  dendrites  are  nutritive  organs  exclusively,  is  at  the 
present  time  replaced  by  the  belief  that  nervous  impulses  also 
travel  along  the  branches  of  the  protoplasmic  process.  The 
anatomic  fact  that  the  fibrils  of  the  axis-cylinder  have  been 
traced  through  the  body  of  the  cell  into  the  dendrons,  seems  to 
substantiate  this  theory. 

It  is  a  most  important  fact  that  the  nerve-unit,  or  the  "  neu- 
rone" of  some  writers — that  is,  the  nerve-cell  and  its  branches — does 
not  anastomose  or  join  with  any  other  nerve-unit,  but  the  terminal 
twigs  or  arborizations  of  one  intertwine  with  those  of  another,  and 
nerve-impulses  may  thus  pass  from  one  to  the  other.  This  inter- 
twining is  called  synapse,  a  word  literally  meaning  a  clasping. 
This  subject  will  be  again  referred  to  when  the  physiology  of 
nerves  is  discussed. 

Neuroglia  (Fig.  79). — This  is  sometimes  spoken  of  as  a  con- 
nective tissue,  but  it  is  in  structure  unlike  connective  tissue  as  we 
have  studied  it.  It  is  also  unlike  it  chemically,  consisting  of 


NEUROGLIA. 


73 


neurokeratin.     Its  origin  from  fhe  epiblast  also  differentiates  it 
from  connective  tissue,  which  arises  from  the  mesoblast. 

Neuroglia  is  the  supporting  tissue  of  the  nerve-cells  and  nerve- 
fibers  of  the  brain  and  spinal  cord.  It  consists  of  cells  and  fibers. 
In  describing  ciliated  epithelium  it  will  be  remembered  that  among 
the  locations  in  which  it  was  found  the  ventricles  of  the  brain 
and  the  central  canal  of  the  spinal  cord  were  mentioned.  From 
the  attached  ends  of  these  cells  branching  neuroglia-fibers  pass  to 
the  surface  of  the  brain  and  the  cord,  and  terminate  at  the  pia  mater 
in  enlargements.  Other  fibers  of  the  neuroglia  arise  from  cells, 
neuroglia,  glia-  or  spider-cells,  which  are  stellate  in  shape.  These 
fibers  aid  in  supporting  the  nerve-cells  and  nerve-fibers. 

Development  of  Nerve-cells  and  Nerve-fibers.— The 
following  description  is  from  Schafer:  "All  nerve-cells  in  the 
body  are  developed  from  the  cells  of  the  neural  groove  and  neural 
crest  of  the  early  embryo;  the  neural  groove  closing  to  form  the 
neural  canal,  the  cells  of  which  form  the  spinal  cord  and  brain, 
and  the  neural  crest  giving  off,  at  intervals,  sprouts  which  become 
the  rudiments  of  the  ganglia.  The  cells  which  line  the  neural 
canal  are  at  first  all  long,  columnar  cells,  but  among  these,  and 
probably  produced  by  a  metamorphosis  of  some  of  these,  rounded 
cells  (neuroblasts)  make  their  appearance,  and  presently  from  each 
one  a  process  begins  to  grow 
out.  This  is  the  axis-cylinder 
process  (neuron)  and  is  char- 
acterized by  its  enlarged  ex- 
tremity. As  it  grows,  it  may 
emerge  from  the  anterolateral 
regions  of  the  canal  and  be- 
come a  motor  neuron  or  ante- 
rior root-fiber.  The  dendrons 
appear  somewhat  later  than  the 
neuron.  The  axis-cylinder 
processes  of  some  of  the  neu- 
roblasts remain  Avithin  the 
nerve-centers,  and  are  devel- 
oped into  association  or  intra- 
central  fibers. 

"The  sprouts  from  the 
neural  crest  contain  the  neu- 
roblasts from  which  the  pos- 
terior root-fibers  are  devel- 
oped. Neurons  grow  out  from 
these  neuroblasts  in  two  directions,  so  that  the  cells  become  bipo- 
lar, one  set,  forming  the  posterior  root-fibers,  grow  into  the  pos- 
terolateral  portion  of  the  spinal  cord,  and  ramify  in  the  develop- 
ing gray  matter ;  the  other  set,  containing  the  afferent  fibers  of  the 


FIG.  79.— Neurogliar  cells  :  a,  from  spinal 
cord  of  embryo  of  cat ;  6,  from  brain  of  adult 
cat ;  stained  in  chrome  silver  (Huber). 


74  NER  VO  US  TISSUE. 

mixed  nerves,  grow  toward  the  developing  anterior  roots,  and 
eventually  mingle  with  them  to  form  the  mixed  nerves.  As 
development  proceeds,  the  bipolar  ganglion-cells  become  gradu- 
ally transformed  in  most  vertebrates  by  the  shifting  of  the  two 
neurons,  into  unipolar  cells ;  but  in  many  fibers  the  cells  remain 
permanently  bipolar. 

"The  ganglia  on  the  sympathetic  and  on  other  peripheral 
nerves  are  formed  from  small  masses  of  neuroblast-cells,  which 
separate  off  from  the  rudiments  of  the  spinal  ganglia  and  give 
origin  to  neurons  and  dendrons  much  in  the  same  way  as  do  the 
neuroblasts  within  the  central  nervous  system. 

"  The  manner  in  which  the  medullary  sheath  and  neurolemma 
of  the  nerve-fibers  are  formed  is  not  well  understood.  The  neuroglia- 
cells  appear  to  be  developed  from  cells  which  are  at  first  similar 
to  the  neuroblasts,  but,  in  place  of  giving  off  a  neuron  and  den- 
drons, a  number  of  fine  processes  grow  out  from  the  cell  in  all 
directions,  forming  the  fibers  of  the  neuroglia." 

Chemistry  of  Nervous  Tissue.— The  following  is  the 
analysis  of  the  brain  of  an  ox  by  Petrowsky : 

Gray  Matter.  White  Matter. 

Water 81.60  per  cent.  68. 30  per  cent. 

Solids 18.40   "     «  31.70  "     " 

100.00  100.00 

The  percentage  composition  of  the  solids  is  as  follows : 

Gray  Matter.  White  Matter. 

Proteids 55.37  24.72 

Lecithin 17.24  9.90 

Cholesterin  and  fat 18.68  51.91 

Cerebrins         0.53  9.55 

Other  organic  compounds  (including  neurokera- 

tin  and  protagon) 6.71  3.34 

Salts 1.45  0.57 

Halliburton  divides  the  solid  constituents  of  the  nervous  tissues 
into  the  following  classes  : 

a.  Proteids. — These  comprise  a  very  considerable  percentage 
of  the  solids,  especially  in  the  gray  matter  (over  50  per  cent.). 

6.  Neurokeratin  and  nuclein. 

c.  Phosphorized  constituents,  especially  protagon  and  lecithin. 

d.  Cerebrins. — Nitrogenous  substances  of  unknown  constitu- 
tion. 

e.  Cholesterin. — Especially  abundant  in  white  matter. 

f.  Extractives. — Creatin,  xanthin,  hypoxanthin,  inosit,  lactic 
acid,  leucin,  uric  acid,  and  urea. 

g.  Gelatin  and  Fat. — From  the  adherent  connective  tissue. 

h.  Inorganic  Salts. — The  total  mineral  matter  varies,  according 
to  different  writers,  from  0.1  to  1  per  cent. 


CHEMISTRY  OF  NERVOUS  TISSUE.  75 

Geoghegan  gives  the  following  as  representing  parts  per  1000 
of  brain : 

Total  ash    .  .    2.9     to  7.1    ,  Chlorin    .  .   0.4    to  1.2 


Potassium 0.6      "1.7 

Sodium 0.4      "1.1 

Magnesium 0.0      "   0.07 

Calcium  .  0.005"   0.02 


PO4 0.9  "2.0 

CO3 0.2  "0.7 

SO4 0.1  "0.2 

Fe(POJ, 0.01  "  0.09 


Halliburton  gives  the  following  table,  which  shows  the  propor- 
tion of  water,  solids,  and  proteids  in  different  portions  of  the 
nervous  system.  The  table  represents  mean  analyses  of  the  organs 
of  adult  human  beings,  dogs,  cats,  and  monkeys : 

Percentage  of 

Water.  Solids.          proteids 

in  solids. 

Gray  matter  of  cerebrum 83.467  16.533  51 

White     "                "              69.912  30.088  33 

Cerebellum 79.809  20.191  42 

Spinal  cord  as  a  whole 71.641  28.354  31 

Cervical  cord 72.529  27.471  31 

Dorsal       "        69.755  30.245  28 

Lumbar    "        72.639  27.631  33 

Sciatic  nerves 61.316  38.684  29 

The  percentage  of  neurokeratin  is  in  gray  matter  0.3 ;  in  white 
matter,  2.2  to  2.9 ;  and  in  nerve,  0.3  to  0.6. 

Proteids  of  Nervous  Tissue. — The  proteids  are :  1.  A  globulin, 
coagulated  by  heat  at  47°  C.,  analogous  to  the  cell-globulin 
derivable  from  cellular  tissues  generally  ;  2.  Nucleoproteid,  which 
coagulates  at  56°-60°  C.  and  contains  0.5  per  cent,  of  phosphorus  ; 
and  3.  A  globulin  coagulating  at  70°-75°  C.,  analogous  to  a  glob- 
ulin obtained  from  the  liver. 

Protagon. — It  was  for  some  time  undecided  whether  this  sub- 
stance, which  was  separated  from  the  brain  by  Liebreich,  was  a 
definite  substance  or  a  mechanical  mixture  of  lecithin  and  cerebrin; 
but  the  evidence  now  at  hand  seems  conclusive  in  favor  of  its 
definiteness  of  chemic  composition.  Its  percentage  composition, 
as  given  by  Garngee  and  Blankenhorn  is  C,  66.39 ;  H,  10.69  ; 
N,  2.39;  P,  1.068;  and  O,  19.462.  The  empirical  formula  is 
C^H^NgPO^.  It  is  probable  that  there  are  more  than  one  pro- 
tagon. 

Cerebrin. — This  constituent  of  nervous  tissue  should  be  spoken 
of  as  cerebrins,  as  there  are  more  than  one.  The  constitution  of 
them  is  not  known.  They  contain  nitrogen  and  yield  galactose 
on  hydration.  They  are  also  called  cerebrosides,  and  are  constitu- 
ents of  the  medullary  sheaths,  and  are  also  found  in  the  yolk  of 
egg,  pus-corpuscles,  and  spleen-cells. 


II.  PHYSIOLOGIC   CHEMISTRY. 


PHYSIOLOGIC  chemistry,  as  applied  to  the  human  body,  may 
be  defined  as  the  science  which  treats  of  the  ingredients  of  the  human 
body  and  of  the  human  food.  These  ingredients  are  spoken  of  by 
some  writers  as  "  proximate  principles,"  by  others  as  the  "  chemical 
basis/'  and  by  still  others  as  "  physiologic  ingredients."  The  latter 
term  is  the  one  which  will  be  adopted,  as  it  is  the  most  expressive. 

If  the  human  body  is  analyzed  into  its  ultimate  chemical  ele- 
ments, it  will  be  found  that  of  the  sixty-nine  elements  known  to 
chemists  no  less  than  fifteen  are  constantly  present.  These  elements 
are  oxygen,  carbon,  hydrogen,  nitrogen,  calcium,  sodium,  potas- 
sium, iron,  phosphorus,  sulphur,  magnesium,  chlorin,  fluorin,  sil- 
icon, and  iodin.  Some  authorities  place  lithium  also  in  this  list. 
As  fluorin  and  silicon  occur  in  such  small  proportions,  they  may 
be  omitted  from  consideration  altogether. 

To  obtain  most  of  these  substances  in  their  elementary  form 
such  processes  must  be  adopted  as  will  utterly  destroy  the  tissues. 
In  the  body,  in  its  living  state,  most  of  these  substances  do  not 
exist  in  their  elementary  condition ;  and,  however  interesting  it 
may  be  to  know  all  the  facts  about  them,  still  a  knowledge  of  the 
properties  of  these  elements  does  not  help  to  an  understanding  of 
their  offices  in  the  human  body.  What  is  really  desired  to  be 
known  is,  under  what  forms  these  elements  exist  in  the  body  during 
life,  and  not  what  can  be  obtained  by  the  analytic  chemist. 

Chemical  elements  and  physiologic  ingredients  are  not  inter- 
changeable terms.  A  physiologic  ingredient  may  be  defined  as 
a  substance  which  exists  in  the  body  under  its  own  form.  To  deter- 
mine, then,  whether  a  given  substance  is  or  is  not  a  physiologic 
ingredient  of  the  human  body,  it  must  be  ascertained  whether  it 
does  or  does  not  exist  there  under  its  own  form.  For  instance, 
if  it  is  asked  if  carbon  is  a  physiologic  ingredient,  before  the 
question  could  be  answered  we  should  have  to  determine  whether 
carbon  exists  in  the  body  under  its  own  form — that  is,  as  carbon. 

Chemistry  demonstrates  that  carbon,  as  an  element,  is  found  in 
nature  in  but  three  forms,  namely,  as  coal,  as  the  diamond,  and  as 
graphite  or  plumbago.  In  the  human  body  none  of  these  sub- 
stances is  found ;  therefore  carbon  does  not  exist  under  its  own 
form,  and  consequently  is  not  a  physiologic  ingredient,  although 

76 


CLASSIFICATION  OF  PHYSIOLOGIC  INGREDIENTS. 


77 


more  than  one-eighth  of  the  body  is  made  up  of  carbon,  and  this 
amount  can  be  obtained  from  it.  But  this  carbon  does  not  exist 
under  its  own  form — that  is,  free  or  uncombined — but  it  is  all  in 
a  state  of  combination,  as  carbonates  or  in  carbohydrates  or  other 
forms  of  combination,  and  when  we  obtain  the  carbon  as  an  ele- 
ment these  combinations  are  broken  up  and  the  carbon  is  set  free. 
Water  is  a  physiologic  ingredient,  because  it  exists  in  the  body 
under  its  own  form,  and  can  be  obtained  therefrom  without  the 
use  of  such  violent  means  as  are  necessary  to  destroy  chemical 
combinations. 

It  is  exceedingly  important  to  have  a  clear  conception  of  what 
are  and  what  are  not  physiologic  ingredients :  all  that  can  be 
learned  of  them  and  their  properties  will  be  of  assistance ;  but  a 
knowledge  of  the  properties  of  their  chemical  elements  will  be  of  no 
special  aid  in  our  physiologic  studies,  for  the  properties  of  a  com- 
pound are  not  the  sum  of  the  properties  of  its  component  parts. 
One  might  be  thoroughly  conversant  with  the  properties  of  oxygen 
and  hydrogen,  and  yet  have  no  possible  conception  of  the  proper- 
ties of  water,  which  their  combination  forms. 

Classification  of  Physiologic  Ingredients.— The  physio- 
logic ingredients  of  the  human  body  may  be  -classified  as  fol- 
lows :  Inorganic ;  Carbohydrates ;  Fats  ;  Proteids ;  Albuminoids ; 
Enzymes.  Other  ingredients  will  be  discussed  in  connection  with 
the  solids  or  liquids  in  which  they  occur. 


Water. 


INORGANIC  INGREDIENTS. 


Salts 


Sodium 


Potassium  .  . 

Calcium     .  . 

Magnesium  . 

Ammonium  . 


Chlorid. 

Phosphate. 

Biphosphate. 

Sulphate. 

Carbonate. 

Bicarbonate. 


C  Chlorid. 
j   Phosphate. 
}   Sulphate. 
(^  Carbonate. 

T  Phosphate. 
<  Carbonate. 
(  Fluorid. 

f  Phosphate. 
(  Carbonate. 

Chlorid. 


78  INORGANIC  INGREDIENTS. 

aSL  }«**»•    I 

lodin. 

Oxygen. 

Hydrogen. 

Nitrogen. 

Marsh-gas. 

Ammonia. 

Sulphuretted  Hydrogen. 

Hydrochloric  Acid. 

Carbon  Dioxid. 

Water  (H2O). — Water  is  one  of  the  most  important  of  the 
physiologic  ingredients.  Its  quantity  in  the  human  body  is  vari- 
ously stated  by  different  authorities :  Halliburton  placing  it  at 
58.5  per  cent,  of  the  body- weight  of  an  adult,  and  66.4  per  cent, 
of  that  of  infants,  while  others  give  it  as  68  per  cent.  It  is  found 
in  all  the  tissues,  both  solid  and  fluid. 

Quantity  of  Water  in  the  Body. — The  percentage  of  water  in 
some  of  the  solids  and  fluids  of  the  body  is  as  follows : 

Enamel  of  teeth 0.2 

Dentin .    .  10. 

Bones  (undried) 50. 

Costal  cartilage 67.66 

Corpuscles  of  venous  blood 68.16 

Muscles 73. 

Human  milk 87. 

Plasma  of  venous  blood 90.15 

Urine 93. 

Gastric  juice 98. 

Perspiration .• 98. 

Saliva 99. 

Pulmonary  vapor 99. 

From  this  table  it  will  be  seen  that  while  water  makes  up  but 
a  small  part  of  the  enamel  of  the  teeth,  it  constitutes  almost  the 
whole  of  the  saliva.  Between  these  two  extremes  it  is  present 
in  different  tissues  in  varying  proportions.  It  should  be  said  of 
these,  and  of  most  other  quantities  given  in  physiologic  tables, 
that  they  are  not  invariable,  hence  the  analyses  of  different  author- 
ities will  vary.  The  composition  of  the  milk,  for  instance,  is  not 
always  the  same ;  therefore  there  will  not  invariably  be  87  per 
cent,  of  water  present;  but  the  normal  variations  from  this  figure, 
either  above  or  below,  will  not  be  very  great,  and  the  percentages 
given  in  the  above  table  may  be  regarded  as  averages. 

Offices  of  Water. — We  should  naturally  infer  from  the  large 
quantity  of  water  present  in  the  body,  and  from  its  universal 
presence  in  all  the  solids  and  liquids,  that  its  offices  must  be 
important ;  and  a  study  of  these  demonstrates  that  this  is  a  fact. 
It  is  the  water  which  gives  to  fluids  their  fluidity.  Without  this 
property  the  blood  could  not  circulate  through  the  blood-vessels, 


WATER.  79 

nor  dissolve  and  hold  in  solution  the  nutritive  materials  which 
it  supplies  to  the  tissues,  nor  carry  the  waste  materials  to  the  vari- 
ous organs  whose  duty  it  is  to  eliminate  them.  Without  water  the 
saliva  would  cease  to  be  the  important  agent  it  is  in  softening  the 
food  in  the  mouth  preparatory  to  its  being  swallowed.  In  short, 
without  water  as  an  integral  part  of  the  fluids  of  the  body  these 
fluids  wrould  cease  to  be  fluids,  and  the  many  and  varied  offices 
which  they  subserve  would  at  once  be  abolished,  and  life  could  no 
longer  be  maintained. 

Equally  important,  though  less  apparent,  are  the  various  offices 
which  are  subserved  by  water  in  the  solids  of  the  body.  From 
the  above  table  it  is  seen  that  water  exists  in  the  muscles  to  the 
amount  of  73  per  cent.  The  striking  property  of  muscles  is  their 
power  of  contractility,  or  ability  to  shorten.  By  the  exercise  of 
this  property  all  the  movements  of  the  different  parts  of  the  body 
are  accomplished  :  without  this  power  locomotion  would  be  impos- 
sible, the  movements  of  the  heart  would  cease,  and  death  would 
quickly  supervene.  A  muscle  deprived  of  its  water  would  cease 
to  possess  this  contractile  power — in  other  words,  would  lose  its 
characteristic  function.  It  must  not  be  inferred  from  this,  how- 
ever, that  it  is  to  the  water  that  muscles  owe  their  contractility, 
but  simply  that  its  presence  is  one  of  the  conditions  essential  to 
the  exercise  of  this  power.  As  will  be  seen  later,  the  skin  pos- 
sesses most  important  functions — those,  for  instance,  of  sensation, 
of  excretion,  and  of  protection.  All  these  functions  would  be 
destroyed  if  the  water  in  the  skin  was  expelled.  Perhaps  this 
fact  is  nowhere  more  strikingly  evident  than  in  studying  the  func- 
tions of  the  skin  of  the  palm  of  the  hand.  The  pliability  of  this 
portion  of  the  skin,  by  which  objects  are  grasped,  and  the  sense 
of  touch,  by  which  it  can  be  determined  whether  they  are  hard 
or  soft,  whether  rough  or  smooth,  whether  hot  or  cold,  are  both 
dependent  on  the  presence  of  water  in  the  skin,  and  the  mere 
evaporation  of  the  water  would  at  once  make  the  skin  hard  and 
rigid,  its  pliability  would  vanishj  and  its  functions  would  cease. 

Sources  of  Water. — The  water  which  exists  in  the  body  is  derived 
from  two  principal  sources  :  First,  from  the  food,  and  second,  from 
its  formation  in  the  interior  of  the  body,  the  former  being  the 
main  source  of  supply.  As  water  is  a  constituent  part  of  every 
tissue  of  the  human  body,  so  it  is  of  all  the  varieties  of  food,  both 
solid  and  liquid,  taken  into  the  body. 

The  quantity  of  water  in  food  (percentage)  is  as  follows : 

Wheat  bread  (fresh) 33 

Mackerel 70 

Lean  beef 70 

Potato 76 

Human  milk 87 

Cows'  milk 87 

Green  vegetables 88 


80  INORGANIC  INGREDIENTS. 

From  this  table  it  will  be  seen  that  the  greater  part  of  potato  and 
of  green  vegetables  is  water,  and  that  even  of  bread,  water  con- 
stitutes a  third.  In  other  words,  three  of  every  four  pounds  of 
potatoes  and  one  of  every  three  pounds  of  bread  are  water.  In 
some  vegetables,  such  as  the  turnip,  about  90  per  cent,  is  water. 
In  liquid  food,  as  milk,  tea,  and  coffee,  the  proportion  of  water  is, 
of  course,  still  greater.  The  amount  of  water  daily  taken  into 
the  body  in  solid  and  liquid  food  aggregates  2000  c.c.  In  addition 
to  this  there  is  a  small  amount  actually  formed  within  the  body. 

One  of  the  important  ingredients  of  food  is  the  class  of  carbo- 
hydrates. A  study  of  their  composition  shows  that  hydrogen  and 
oxygen  exist  in  these  substances  in  such  proportion  as  to  form 
water.  In  the  various  changes  which  these  elements  undergo  in 
the  body  water  is  formed.  Besides  this  source  there  is  reason  to 
believe  that  a  small  quantity  of  water  is  formed  by  the  action 
of  free  oxygen  on  some  organic  substances.  The  amount  of  water 
daily  formed  in  these  two  ways  is  not  far  from  500  c.c.,  which 
makes,  with  the  water  taken  in  with  the  food,  a  total  of  2500  c.c. 

Avenues  of  Discharge  from  the  Body. — The  water  which  has 
been  shown  to  form  so  essential  a  part  of  the  body  is  not,  how- 
ever, a  permanent  ingredient — that  is,  while  water  is  always  pres- 
ent, it  is  not  the  same  water  :  that  which  at  one  time  exists  in  the 
tissues  is  soon  replaced  by  other  water.  The  amount  daily  dis- 
charged is  equal  to  the  amount  taken  in  with  the  food  and  formed 
in  the  body — that  is,  about  2500  c.c.  The  avenues  by  which 
it  passes  out,  and  the  proportion  by  each,  are  as  follows : 

Large  intestine,  as  feces 4  per  cent. 

Lungs,  as  watery  vapor 20       " 

Skin,  as  perspiration 30       u 

Kidneys,  as  urine 46       u 

When  discharged  it  is  not  pure  water,  but  contains  ingredients 
that  vary  according  to  the  channel  by  which  it  is  eliminated.  The 
composition  of  these  ingredients  respectively  will  be  studied  in  the 
appropriate  places. 

Salts. — Sodium  chlorid  or  common  salt  (NaCl)  is  present  in 
all  the  solids  and  fluids  of  the  body,  except  in  the  enamel  of  the 
teeth.  The  quantity  (percentage)  in  different  solids  and  fluids  is 
as  follows  : 

Milk 0.03 

Saliva 0.15 

Gastric  juice 0.17 

Perspiration ]  0.22 

Blood t   .  o^33 

Urine 0.55 

Bones •   •  / 0.70 

The  total  quantity  of  common  salt  in  the  human  body  is  110 
grams. 

Offices  of  Sodium   Chlorid. — The  most  important  office  which 


SALTS.  81 

sodium  chlorid  subserves  is  in  connection  with  the  process 
known  as  "  osmosis,"  or  the  diffusion  of  liquids'  through  animal 
membranes,  a  subject  which  will  be  discussed  in  connection 
with  the  process  of  absorption.  A  second  office  which  it  pos- 
sesses is  to  hold  in  solution  the  globulins.  TJie  globulins  are 
proteids  which  are  not  soluble  in  distilled  water,  as  are  the  native 
albumins,  but  are  soluble  in  dilute  solutions  of  sodium  chlorid 
(1  per  cent.).  The  so-called  "  normal"  or  "  physiologic"  salt-solu- 
tion is  made  by  dissolving  6  grams  of  sodium  chlorid  in  a  liter  of 
water.  The  importance  of  this  office  of  common  salt  will  be 
more  fully  appreciated  in  the  study  of  the  plasma  of  the  blood, 
of  which  the  globulins  form  an  essential  part.  A  third  office 
which  is  attributable  to  it  is  to  aid  in  the  excretion  of  waste 
matter.  The  sodium  chlorid  of  the  blood  is  the  source  of  the 
hydrochloric  acid  of  the  gastric  juice. 

Source  of  Sodium  Chlorid. — The  food  taken  into  the  body  is 
the  principal  source  of  the  sodium  chlorid  which  the  body  con- 
tains. 

The  quantity  (percentage)  of  this  salt  in  some  articles  of  food 
is  as  follows  : 

Oats 0.01 

Turnip 0.03 

Potato 0.04 

Cabbage 0.04 

Beet 0.06 

It  has  been  the  opinion  of  physiologists  that  sodium  chlorid 
is  not  present  in  sufficient  amount  in  human  food  to  satisfy  the 
demands  of  the  body ;  consequently,  that  an  additional  amount 
must  be  taken  in  as  a  condiment  at  the  table  or  be  added  to 
the  food  during  the  process  of  cooking.  But  Dr.  F.  A.  Cook, 
surgeon  to  the  first  Peary  North-Greenland  Expedition,  states 
that  the  Eskimos  who  dwell  between  the  seventy-sixth  and 
seventy-ninth  parallels  use  no  salt  or  condiment  of  any  kind  in 
their  food,  which  is  entirely  of  meat  and  blubber  only  one-third 
cooked.  This  cooking  is  done  in  order  that  there  may  be  obtained 
the  blood  of  the  meat,  and  this  blood  the  Eskimos  drink.  How- 
ever this  may  be  with  the  Eskimos,  it  is  the  general  experience 
that  by  the  addition  of  salt  the  food  is  not  only  made  more  pala- 
table, but  the  digestive  juices  are  also  increased  and  digestion  im- 
proved. This  insufficiency  of  salt  in  the  food  of  man  is  seen  also 
in  that  of  some  of  the  lower  animals.  While  carnivora  or  flesh- 
eating  animals  find  in  their  food  all  the  salt  they  need,  it  is  differ- 
ent with  the  herbivora  or  vegetable-eaters.  Especially  noticeable 
is  this  fact  in  the  ruminants.  Boussingault  many  years  ago  demon- 
strated this  by  a  series  of  experiments  which  he  conducted.  He 
selected  two  sets  of  bullocks  as  nearly  as  possible  in  the  same 
condition  of  health,  and  to  both  sets  he  gave  the  same  food,  except 


82  INORGANIC  INGREDIENTS. 

that  to  one  he  gave  salt,  while  to  the  other  he  gave  none.  Several 
months  elapsed  before  any  very  marked  difference  could  be  detected, 
but  at  the  end  of  a  year,  during  which  time  the  experiment  con- 
tinued, there  were  striking  differences  in  the  two  sets.  The  bul- 
locks that  received  the  salt  were  in  excellent  physical  condition, 
while  those  deprived  of  it  were  much  inferior  in  every  respect : 
their  hide  was  rough,  their  hair  tangled,  and  they  were  dull  and 
apathetic.  Experiments  of  a  similar  nature  upon  sheep  have  pro- 
duced like  results. 

A  venues  of  Discharge. — Sodium  chlorid  is  daily  discharged 
from  the  body  through  the  following  excretions  and  in  the  given 
amounts :  Urine,  13  grams ;  perspiration,  2  grams.  There  is  a 
small  amount  also  in  mucous  secretions. 

Sodium  Phosphate  (Na2HPO4)  and  Potassium  Phosphate  (K2- 
HPO4). — These  salts  are  so  intimately  associated  that  they  may  be 
described  together.  They  are  frequently  spoken  of  as  the  "  alka- 
line phosphates,"  and  exist  in  all  the  solids  and  fluids  of  the  body. 

Offices  of  Alkaline  Phosphates. — The  most  important  office 
which  these  salts  perform  is  to  assist  in  giving  alkalinity  to  the 
alkaline  fluids — a  property  which,  in  the  blood  at  least,  is  essential 
to  life,  and  in  some  of  the  other  fluids  is  necessary  to  the  per- 
formance of  their  offices.  The  fluids  of  the  body  are,  with  but 
four  exceptions,  alkaline  in  reaction  :  these  exceptions  are  gastric 
juice,  perspiration,  urine,  and  vaginal  mucus.  The  following 
fluids  are  alkaline :  plasma  of  the  blood,  lymph,  aqueous  humor, 
cephalorachidian  fluid,  pericardial  fluid,  synovia,  mucus  (except 
that  of  vagina),  milk,  spermatic  fluid,  tears,  saliva,  bile,  pancreatic 
juice,  and  intestinal  juice. 

The  alkalinity  of  the  plasma  of  the  blood  is  not  an  accidental 
property.  The  fact  that  the  blood  of  all  animals  hitherto  ex- 
amined has  invariably  been  found  alkaline  would  seem  to  indicate 
that  this  condition  is  an  important  one.  Bernard  has  shown  that 
if  an  acid  is  injected  into  the  blood  of  an  animal,  death  will  be 
produced  even  though  the  amount  injected  is  not  enough  to  make 
the  blood  itself  acid.  One  of  the  properties  of  the  blood  is  to 
carry  carbonic  acid  gas — one  of  the  products  of  the  waste  of  the 
tissues — to  the  lungs,  where  it  is  eliminated  ;  and  experiment  has 
shown  that  the  alkalescence  of  the  blood  enables  it  to  carry  more 
of  this  gas  than  it  could  were  it  neutral  in  action.  In  discussing 
the  alkaline  carbonates  it  will  be  seen  that  they  take  part  in 
rendering  alkaline  the  fluids  in  which  they  occur. 

Source  of  Alkaline  Phosphates. — The  alkaline  phosphates  are 
taken  into  the  body  in  the  food,  of  which  they  form  a  constituent 
part. 

Avenues  of  Discharge. — After  fulfilling  their  offices  in  the  body 
these  alkaline  salts  are  discharged  in  the  perspiration,  the  mucus, 
and  the  urine.  In  the  urine  a  portion  of  the  sodium  phosphate 


SALTS.  83 

is  converted  into  sodium  biphosphate,  or,  as  it  is  sometimes  called, 
"  acid  sodium  phosphate,"  which  gives  to  the  urine  its  acid 
reaction.  In  this  fluid  are  discharged  daily  4.5  grams  of  the 
alkaline  phosphates  and  the  sodium  biphosphate. 

Sulphates. — Sodium  sulphate  (NajS04)  and  potassium  sulphate 
(K2SO4)  are  found  in  the  blood,  lymph,  aqueous  humor,  milk, 
saliva,  mucus,  perspiration,  urine,  and  feces.  Their  quantity  is 
small,  however,  except  in  the  urine,  by  which  fluid  they  are  dis- 
charged daily  to  the  amount  of  4  grams. 

Source  of  Sulphates. — These  sulphates  are  taken  in  as  part  of 
the  solid  food  we  eat  and  also  in  the  water  we  drink.  They  are 
present  in  flesh,  in  eggs,  in  the  cereals,  and  in  other  animal  and 
vegetable  foods.  Drinking-water  often  contains  these  sulphates, 
and  calcium  sulphate  as  well.  Sulphates  are  undoubtedly  formed 
to  some  extent  within  the  body.  In  discussing  the  constitution 
of  the  albuminous  ingredients  of  the  food  it  will  be  seen  that  one 
of  their  elements  is  sulphur.  Some  of  this  sulphur  becomes 
oxidized,  forming  sulphuric  acid,  which,  being  a  stronger  acid 
than  carbonic,  displaces  it  from  the  carbonates  and  unites  with 
the  alkaline  bases,  forming  sulphates. 

Carbonates. — Sodium  carbonate  (Na2CO3),  sodium  bicarbonate 
(NaHCOj),  and  potassium  carbonate  (K2CO3)  are  salts  which  are 
known  as  the  "  alkaline  carbonates/'  and  are  intimately  associated 
with  the  alkaline  phosphates. 

Source  of  Carbonates. — These  salts  are,  to  some  extent,  intro- 
duced with  the  food,  but  are  principally  formed  by  the  decom- 
position of  the  salts  of  the  vegetable  acids.  In  fruits,  such  as 
apples  and  cherries,  and  in  vegetables,  such  as  potatoes  and  carrots, 
are  found  malic,  tartaric,  and  citric  acids,  united  with  sodium  and 
potassium  to  form  malates,  tartrates,  and  citrates  of  sodium  and 
potassium.  When  these  fruits  or  vegetables  are  eaten,  these  salts 
are  taken  up  by  the  blood,  and  while  in  the  blood  the  organic  acids 
are  decomposed,  and  the  bases  uniting  with  carbonic  acid,  alkaline 
carbonates  are  formed,  which  are  discharged  in  the  urine.  This 
accounts  for  the  fact  that  after  eating  sufficient  of  such  fruits  or 
vegetables  the  urine  becomes  alkaline. 

Office  of  Carbonates. — The  alkalinity  of  the  blood  and  of  other 
alkaline  fluids  is,  as  has  been  stated,  only  partially  due  to  the 
alkaline  phosphates.  In  causing  this  reaction  the  alkaline  car- 
bonates have  a  share.  In  the  blood  of  flesh-eating  animals  the 
phosphates  are  more  abundant,  this  being  due  to  the  predominance 
of  phosphates  in  muscular  tissue,  while  in  that  of  the  herbivora 
the  carbonates  are  in  excess  of  the  phosphates.  Remembering, 
then,  what  has  been  said  of  the  formation  of  the  carbonates  from 
the  salts  in  fruits  and  vegetables,  this  difference  in  the  blood  is 
readily  understood.  In  human  blood  there  are  both  phosphates 
and  carbonates  to  account  for  its  alkalinity. 


84 


INORGANIC  INGREDIENTS. 


Potassium  Chlorid. — Potassium  chlorid  (KC1)  is  found  in  many 
of  the  tissues,  especially  in  the  muscles,  in  blood-corpuscles,  and 
in  milk.  This  salt  occurs  also  in  gastric  juice,  in  urine,  and  in 
perspiration.  Like  sodium  chlorid,  it  is  neutral  in  reaction  and 
is  soluble  in  water. 

Source  of  Potassium  Chlorid. — Potassium  chlorid  is  contained 
in  both  animal  and  vegetable  foods. 

Avenues  of  Discharge. — Potassium  chlorid  is  discharged  in 
mucus,  in  urine,  and  in  perspiration. 

Calcium  Salts — Calcium  Phosphate,  Lime  Phosphate,  or  Phosphate 
of  Lime  (Ca3(PO4)2). — Next  to  water,  calcium  phosphate  is  the 
most  abundant  physiologic  ingredient  of  the  human  body.  Its 
total  amount  is  2400  grams  in  a  man  weighing  65  kilograms. 

The  quantity  (percentage)  of  calcium  phosphate  is  as  follows  : 

Blood  0.03 

Urine 0.07 

Milk , 0.27 

Bone 57.6 

Enamel  of  teeth 88.5 

The  greater  part  of  the  calcium  phosphate  in  the  body  is  in  the 
bones.     It  is  estimated  that  6.4  per  cent,  of  the  body  is  bone,  and 
in  a  man  weighing  65  kilograms,  an  average  weight,  there  would 
therefore  be  2400  grams  of  this  salt.     Its  presence 
in  the  fluids  of  the   body  is  not  in  noteworthy 
amount,  except  in  the  milk. 

Office  of  Calcium  Phosphate. — The  principal 
office  of  calcium  phosphate  is  to  give  to  the  bones 
their  rigidity.  During  early  life  this  salt  is  in  small 
amount  in  the  bones,  and  at  this  time  the  bones 
are  soft  and  yielding.  Later,  as  the  phosphate  and 
other  inorganic  ingredients  are  deposited  in  greater 
amount,  these  structures  become  more  rigid  and 
better  adapted  to  sustain  weight.  In  old  age  the 
inorganic  constituents  are  in  excess  of  the  organic, 
and  besides  this  difference  in  the  proportion  of 
organic  and  inorganic  constituents  there  is  the 
further  difference  that  the  bones  of  the  old  are 
lighter  in  weight  and  more  porous.  This  is  due 
to  an  increase  in  the  size  of  the  medullary  canal 
and  the  cancel  Ions  spaces,  brought  about  by  absorp- 
tion ;  this  is  especially  marked  at  the  'articular 
head.  There  is  also  sometimes  a  fatty  change  in 
the  bone-tissue.  These  changes  constitute  senile  atrophy  of  the 
bones.  At  an  advanced  period  of  life  the  bones  are  easily  bro- 
ken ;  while  in  infancy  they  bend  but  do  not  break,  or  if  they  do 
break,  the  fracture  is  not  complete,  but  is  similar  to  that  which 
occurs  in  a  green  stick,  and  is  known  as  the  "green-stick  fracture" 


FIG.  80.— Par- 
tial or  "  green - 
stick "  fracture 
(Stimson). 


SALTS. 


85 


(Fig.  80).  The  flexible  condition  of  the  bones  may  be  artificially 
produced  by  putting  a  long  bone,  like  the  fibula,  into  a  jar  contain- 
ing dilute  hydrochloric  acid.  The  acid  dissolves  the  inorganic  salts, 
and,  although  in  appearance  the  bone  is  much  the  same  as  before, 
it  will  now  be  found  so  flexible  as  to  permit  its  being  tied  in  a 
knot  (Fig.  81).  In  the  blood,  calcium  phos- 
phate, which  is  insoluble  in  alkaline  fluids,  is 
held  in  solution  by  the  albuminous  constituents. 
Were  these  withdrawn  the  calcium  phosphate 
would  at  once  be  rendered  insoluble,  and  would 
be  precipitated. 

Source  of  Calcium  Phosphate.  —  Calcium 
phosphate  is  an  important  ingredient  of  the 
animal  and  vegetable  food  of  man.  It  is 
contained  in  flesh,  in  eggs,  in  milk,  in  wheat, 
in  oats,  in  rice,  in  peas,  in  beans,  in  potatoes, 
in  apples,  in  cherries,  and  in  some  other  ali- 
mentary substances.  Its  presence  in  milk 
needs  especial  comment.  As  has  been  stated, 
during  early  life  calcium  phosphate  is  in  the 
bones  in  small  amount.  The  milk,  upon 
which  the  growing  child  relies  for  its  nour- 
ishment, supplies  the  necessary  amount  of 
this  salt  to  give  the  bones  their  firmness  and 
rigidity.  From  this  statement  it  will  be  seen 
that  the  adulteration  of  milk  with  water,  even 
though  the  water  is  pure,  may  be  of  great  in- 
jury to  the  child.  To  obtain  the  necessary 
amount  of  calcium  phosphate  a  certain  amount 
of  milk  must  be  taken.  If  half  this  amount 
is  water,  the  quantity  of  the  lime-salt  present 
will  be  but  one-half  of  what  it  should  be,  and 
the  child  is  consequently  defrauded.  Of 
course,  if  impure  water  is  used  in  the  adul- 
teration, there  is  the  additional  danger  of 
introducing  the  germs  of  disease  with  the 
milk. 

A  venues     of    Discharge. — A    very    small 
amount   of  calcium    phosphate  is  discharged 
from  the  body — a  fact  which  shows  its  permanent  character.     It 
is  discharged  in  the  urine,  in  the  feces,  and  in  the  perspiration. 

Calcium  Carbonate  (CaCO3). — This  salt  exists  in  the  bones  to 
the  amount  of  about  300  grams,  in  the  teeth,  in  the  blood,  in 
lymph,  in  chyle,  in  the  saliva,  and  sometimes  in  the  urine.  Like 
calcium  phosphate,  with  which  it  is  usually  associated,  it  is  insolu- 
ble in  water ;  and  when  it  exists  in  solution  its  solubility  is  due 
either  to  alkaline  chlorids  or  to  free  carbonic  acid. 


FIG.  81. — Bone  tied 
in  knot. 


86  INORGANIC  INGREDIENTS. 

Calcium  Fluorid  (CaFl2)  exists  in  the  bones  and  in  the  teeth, 
and  is  of  little  importance. 

Magnesium  Salts. — Magnesium  phosphate  (Mg3PO4)  is  found 
wherever  calcium  phosphate  is  found,  and  the  two  together  are 
frequently  spoken  of  as  the  "  earthy  phosphates."  It  is  discharged 
by  the  urine. 

Magnesium  Carbonate  (MgCO3). — A  trace  of  this  salt  is  found 
in  the  blood. 

Ammonium  Salts. — Traces  of  ammonium  chlorid  (NH4C1)  are 
found  in  the  gastric  juice  and  in  the  urine. 

Iron. — Iron  is  present  in  the  hemoglobin  of  the  blood,  in  the 
hair,  the  bile,  and  the  urine.  Its  presence  in  the  coloring-matter 
of  the  blood  is  its  most  striking  characteristic.  It  exists  in  the 
blood  combined  with  the  other  chemical  elements,  and  not  as  an 
oxid.  The  total  amount  of  iron  in  the  blood  of  the  body  of  a 
man  weighing  65  kilograms  is  about  2.71  grams. 

Office  of  Iron. — The  office  of  iron  is  not  understood.  It  is  re- 
garded as  a  remarkable  fact  that  without  iron  chlorophyll,  the  green 
coloring-matter  of  plants,  cannot  be  formed — in  other  words,  that 
vegetable  life  is  interfered  with  ;  and  it  is  believed  that  its  pres- 
ence in  the  coloring-matter  of  the  blood  of  an  animal  is  equally 
necessary  for  its  nutrition. 

Source  of  Iron. — All  animal  food  containing  blood  contains 
iron.  In  addition  to  this,  iron  is  taken  into  the  body  in  rye, 
barley,  oats,  wheat,  peas,  and  strawberries. 

Avenues  of  Discharge. — A  small  amount  only  of  iron  is  dis- 
charged in  the  bile  and  the  urine.  After  serving  its  purpose  in 
the  blood  it  is  probably  deposited  in  the  hair. 

lodin  (I). — This  element  occurs  in  the  thyroid  gland. 

Silicon  (S). — It  is  not  known  in  exactly  what  form  silicon 
exists  in  the  body,  possibly  as  silicic  acid. 

Oxygen  (O). — This  gas  is  absorbed  from  the  air,  and  exists 
in  the  blood  principally  in  loose  combination  with  the  hemoglobin, 
though  some  of  it  is  doubtless  free. 

Hydrogen  (H). — Hydrogen  is  found  in  the  alimentary  canal 
and  in  the  expired  air,  having  been  absorbed  by  the  blood  from 
the  intestine. 

Nitrogen  (N). — Nitrogen  is  absorbed  from  the  air  by  the 
blood,  in  which  it  exists  in  a  dissolved  state.  Some  nitrogen  is 
formed  also  within  the  body. 

Marsh-gas  (CH4). — This  gas  is  found  in  the  expired  air,  like 
hydrogen,  having  been  absorbed  from  the  intestines.  Reiset  found 
that  thirty  liters  were  expired  in  twenty-four  hours. 

Ammonia  (NH3). — A  small  amount  of  ammonia  is  found  in 
the  expired  air,  probably  derived  from  the  blood. 

Sulphuretted  Hydrogen  (H2S). — This  gas  is  found  in  the 
intestines. 


CARBOHYDRATES.  87 

Hydrochloric  Acid  (HC1). — Hydrochloric  acid  exists  in  the 
gastric  juice. 

Carbon  Dioxid  (CO2). — This  gas  exists  in  many  of  the 
fluids,  having  been  absorbed  by  them  from  the  tissues.  It  is  also 
present  in  blood  and  in  expired  air. 

CARBOHYDRATES. 

This  class  is  so  called  because  its  members  contain  hydrogen 
and  oxygen  in  the  proportion  to  form  water,  united  with  carbon. 
All  substances,  however,  which  have  this  composition  are  not 
carbohydrates,  e.  g.,  acetic  acid  (C2H3OOH),  nor  is  it  to  be  inferred 
that  a  carbohydrate  is  a  compound  in  which  water  is  simply  joined 
to  carbon ;  on  the  contrary  its  constitution  is  quite  complex. 

Most  of  the  members  of  this  class  which  are  of  physiologic 
interest  contain  six  atoms  of  carbon  or  a  multiple  of  that  number, 
and  are,  therefore,  hexoses. 

Carbohydrates  are  classified  as  Monosaccharids  or  Glucoses, 
Disaccharids  or  Saccharoses,  and  Polysaccharids  or  Amyloses. 

Monosaccharids  or  Glucoses. — The  members  of  this 
group  have  the  chemical  formula  C6H12O6.  Those  which  are^of 
special  interest  are  Dextrose,  Levulose,  and  Galactose. 

Dextrose  (glucose,  grape-sugar,  diabetic  sugar)  is  normally 
found  in  the  blood,  chyle,  lymph,  and  in  very  small  amount  in 
the  urine.  It  occurs  in  grapes  and  some  other  fruits,  and  also 
in  honey.  Dextrose  and  levulose  usually  occur  together.  In  the 
disease  known  as  "  diabetes  mellitus  "  the  quantity  of  dextrose  in 
the  blood  and  urine  is  very  much  increased.  It  is  a  substance  of 
much  interest,  as  it  is  in  the  form  of  dextrose  that  the  carbo- 
hydrates of  the  food  find  their  way  into  the  blood.  In  its  pure 
state  dextrose  is  colorless  and  readily  crystallizes  ;  it  is  soluble 
in  cold,  more  so  in  hot  water.  It  is  dextrorotatory,  whence  it 
derives  its  name.  In  alkaline  solutions  dextrose  reduces  metallic 
oxids,  a  property  which  is  made  use  of  in  determining  its  pres- 
ence and  in  measuring  its  quantity. 

Various  tests  are  employed  for  the  detection  of  dextrose ; 
among  these  are  Trommer's,  the  fermentation-test,  and  Fehling's. 

Trommer's  Test. — The  method  of  applying  this  test  is  as 
follows : 

If  the  presence  of  dextrose  in  an  organ  is  to  be  ascertained,  this 
should  be  cut  into  small  pieces  and  boiled  with  water  and  sulphate 
of  sodium,  and  the  mixture  filtered  in  order  to  have  a  clear  solu- 
tion, which  is  essential.  Some  of  this  should  be  poured  into  a 
test-tube,  and  a  few  drops  of  a  solution  of  sulphate  of  copper 
added.  To  this  a  solution  of  caustic  potash  should  be  added,  so 
as  to  make  the  contents  of  the  tube  distinctly  alkaline.  The  tube 
should  now  be  heated,  when,  if  dextrose  is  present,  just  before  the 


88  CARBOHYDRATES. 

boiling-point  is  reached,  a  reddish  precipitate,  consisting  of  cup- 
rous oxide,  will  form.  Levulose,  galactose,  lactose,  and  maltose 
have  reducing  power  similar  to  that  of  dextrose,  but  differing  in 
degree ;  thus,  the  power  of  lactose  as  compared  with  dextrose  is 
but  that  of  7  to  10,  while  maltose  has  one-third  less  power  than 
dextrose.  Cane-,  maple-,  and  beet-sugar  have  no  reducing  power, 
and  must  first  be  converted  into  dextrose  before  the  reaction  will 
take  place. 

Fermentation-test. — This  test  depends  upon  the  fact  that  under 
the  influence  of  yeast  dextrose  is  decomposed  into  ethyl  alcohol 
and  carbonic  anhydrid. 

Fehling's  Test. — This  test  is  based  on  the  same  principle  as  that 
of  Trommer,  namely,  the  property  possessed  by  dextrose  to  reduce 
metallic  oxids.  It  is  employed  not  only  to  determine  the  presence 
of  dextrose,  but  also  to  measure  the  quantity  present.  The  test- 
solution  is  liable  to  undergo  changes  which  invalidate  the  result ; 
it  should,  therefore,  be  freshly  prepared,  or  at  least  be  boiled  be- 
fore it  is  used.  The  principal  change  which  takes  place  is  the 
formation  of  racemic  acid  from  the  tartaric  acid  of  the  solution, 
and  this  has  the  same  reducing  action  as  the  sugar.  If  after 
boiling  the  solution  is  clear,  it  may  be  inferred  that  decomposition 
has  not  taken  place,  and  it  may  be  used.  The  solution  is  prepared 
in  the  following  manner : 

34.639  grams  of  pure  recrystallized  copper  sulphate  are  dis- 
solved in  distilled  water,  which  is  made  up  to  500  c.c.  This  solu- 
tion should  be  kept  separate  from  the  second  solution,  which  is 
made  by  dissolving  175  grams  of  crystallized  Rochelle  salts  and 
60  grams  of  sodium  hydroxid  in  distilled  water,  and  likewise 
made  up  to  500  c.c.  It  is  found  by  experience  that  when  these 
two  solutions  are  mixed  the  resulting  mixture  does  not  keep  well. 
When  the  test  is  to  be  made  equal  quantities  of  the  two  solu- 
tions are  mixed.  Prof.  Bartley's  method  of  applying  this  test  in 
urine  is  as  follows :  10  c.c.  of  the  solution  are  measured  into  a 
suitable  flask.  To  this  10  c.c.  of  a  freshly  prepared  10  per  cent, 
solution  of  potassium  ferrocyanid  are  added,  and  about  30  c.c. 
of  water.  The  mixture  is  heated  on  a  water-bath,  and  the  urine, 
previously  diluted  with  water  if  it  contains  much  sugar,  is  run 
in  from  a  faucet,  drop  by  drop,  until  the  blue  color  just  dis- 
appears. The  addition  of  the  slightest  excess  of  sugar  shows 
itself  by  the  solution  becoming  quickly  brown.  By  careful  com- 
parative tests  Prof.  Bartley  has  found  this  method  to  be  reliable 
and  accurate  provided  the  solution  is  not  boiled  during  the  reduc- 
tion. The  best  temperature  he  finds  to  be  between  80°  and  90°  C. 

Polariscope. — This  is  also  known  as  a  polarimeter.  It  may  be 
employed  to  determine  the  presence  of  dextrose.  In  order  to 
understand  the  use  of  this  instrument  it  will  be  necessary  to  con- 
sider briefly  the  subject  of  the  polarization  of  light. 


MONOSACCHARIDS  OR  GLUCOSES.  89 

Common  light  is  due  to  vibratory  disturbances  in  the  ether, 
which  are  propagated  through  it  as  waves,  the  direction  of  the 
vibrations  being  transverse  to  that  of  propagation.  In  all  places 
where  light  is  polarized  its  vibrations,  still  trans  verse  to  the  direc- 
tion of  the  ray,  are  all  in  one  plane.  Light  may  be  polarized  by 
transmitting  it  through  most  crystals,  and  if  it  is  then  transmitted 
through  another  crystal  it  will  be  observed  that  when  this  is  in 
certain  positions  it  will  pass  most  easily,  and  that  in  positions  at 
right  angles  to  these  it  will  be  quenched  entirely.  It  is  supposed 
that  the  molecular  structure  of  these  crystals  is  such  as  to  make 
them  transparent  for  vibrations  in  one  plane  and  opaque  to  those  in 
the  plane  at  right  angles.  The  rotation  of  the  plane  of  polarization 
by  passing  the  polarized  light  through  a  crystal  constitutes  rotary 
polarization,  and  is  the  principle  upon  which  the  polariscope  is 
constructed. 

The  crystal  which  polarizes  the  light  is  the  polarizer,  and  that 
which  distinguishes  it  is  the  analyzer. 

This  power  to  rotate  the  plane  of  polarization  is  possessed  by 
other  substances  than  crystals,  such  as  solutions  of  various  sub- 
stances, among  them  being  sugar ;  and  as  each  of  these  substances 
rotates  the  plane  through  a  different  number  of  degrees  of  a  circle, 
this  fact  enables  the  investigator  to  determine  with  what  substance 
he  is  dealing.  Substances  having  this  power  of  rotating  the  plane 
of  the  polarized  ray  are  said  to  be  optically  active;  and  those 
which  rotate  it  to  the  right  are  dextrorotatory,  and  those  that 
rotate  it  to  the  left,  levorotatory.  Inasmuch  as  the  rotation  is 
different  for  each  of  the  component  parts  of  white  light,  this  kind 
of  light  cannot  be  used,  but  in  its  stead  light  of  a  single  color, 
monochromatic  light,  must  be  used.  This  is  usually  the  yellow 
light  produced  by  burning  a  salt  of  sodium  in  the  flame  of  a 
Bunsen  burner. 

A  polariscope  or  polari meter  which  is  specially  adapted  to  the 
estimation  of  the  amount  of  sugar  in  a  given  solution  is  called  a 
saccharimeter.  Of  these,  there  are  various  kinds,  the  one  most 
commonly  used  being  Laurent's. 

Laurent's  Polarimeter. — This  and  its  use  are  described  by  Prof. 
Bartley  in  his  Medical  Chemistry  in  the  following  language : 
"  Laurent's  polarimeter  (Fig.  82)  is  one  of  the  simplest  and  best. 
In  this  instrument  one-half  of  the  field  of  vision  is  covered  by  a 
very  thin  plate  of  quartz,  which  slightly  rotates  the  plane  of  the 
light  passing  through  it,  and  causes  some  light  to  pass  even  when 
the  polarizer  and  analyzer,  both  of  which  are  Nicol  prisms,  are 
crossed.  If  the  analyzer  (h)  is  rotated  so  as  to  cause  the  quartz 
plate  to  become  dark,  the  light  passes  through  the  uncovered  half 
of  the  field.  In  an  intermediate  position  the  two  halves  of  the  field 
appear  equally  illuminated.  The  scale  (c)  is  so  graduated  that 
this  position  of  the  analyzer  is  made  the  zero  point  of  the  instru- 


90  CARBOHYDRATES. 

ment.  The  slightest  deviation  of  the  analyzer  from  this  position 
causes  one-half  of  the  field  to  appear  darker  and  the  other  half 
lighter.  There  are  thus  presented  to  the  eye  two  lights  to  be 
compared,  and  the  instrument  is  thus  very  sensitive.  Monochro- 
matic light  must  be  used.  In  some  instruments  the  circle  is 
divided  both  into  degrees  and  sugar  units,  or  percentages.  The 
scale  is  read  by  means  of  a  vernier  and  lens  (n).  Before  using  the 
instrument  the  observation  tube  is  filled  with  water  and  placed  in 
position  between  the  analyzer  and  polarizer.  If  the  instrument 
is  properly  adjusted,  the  zero  mark  on  the  vernier  will  correspond 
with  the  zero  point  of  the  scale  when  the  two  halves  of  the  field 
are  equally  illuminated.  The  tube  is  then  filled  with  the  solution 


FIG.  82. — The  Laurent  shadow  polarizing  sacchari meter. 

to  be  tested  and  again  placed  between  the  analyzer  and  polarizer, 
when,  if  it  is  an  active  substance,  the  plane  of  the  polarized  ray 
coming  from  the  analyzer  will  be  turned  to  the  right  or  to  the  left 
in  passing  through  the  solution,  and  one-half  of  the  field  will  be 
lighter  than  the  other.  The  amount  of  rotation  of  the  plane  of 
the  polarized  ray  will  be  proportioned  to  the  amount  of  the  active 
substance  in  the  solution.  It  will  now  be  necessary  to  rotate  the 
analyzer  (h)  to  the  right  or  to  the  left,  so  that  the  two  halves  of 
the  field  will  again  appear  equally  illuminated.  When  this  has 
been  accomplished  we  may  read  oflf  on  the  vernier  the  degrees 
of  the  circle  through  which  the  analyzer  has  been  rotated.  In 
this  way  the  amount  of  rotation  of  the  polarized  ray  is  deter- 
mined. 


MONOSACCHAEIDS  OR   GLUCOSES.  91 

"  The  specific  rotatory  power  of  any  substance  is  the  amount  of 
rotation  of  the  plane  of  polarized  light  in  degrees  of  a  circle, 
produced  by  1  gram  of  the  substance  dissolved  in  1  c.c.  of  the 
liquid,  examined  in  a  tube  one  decimeter  in  length.  The  specific 
rotatory  power  of  a  substance  is  obtained  by  dividing  the  angular 
rotation  observed  in  the  polarimeter  (a)  by  the  length  of  the  tube 
in  decimeters  (1)  and  by  the  number  of  grams  in  1  c.c.  of  the 
liquid  (w).  If  a  sodium  flame  is  used  as  a  source  of  light,  the 
specific  rotation  of  the  substance  is  that  of  light  with  wave- 
lengths corresponding  to  the  D  line  of  the  solar  spectrum,  and  is 
usually  denoted  by  (a)d.  Then  the  above  statement  may  be  ex- 
pressed as  follows  : 


In  this  formula  plus  indicates  that  the  substance  is  dextrorotatory, 
and  minus  that  the  substance  is  levorotatory.  If  in  this  formula 
the  specific  rotatory  power  of  the  substance  under  examination  is 
known,  and  we  wish  to  find  the  value  of  (w),  the  weight  of  the 
substance,  then  the  formula  becomes, 


In  this  formula  a  is  the  observed  rotation,  I  the  length  of  the  tube 
in  decimeters,  which  is  known,  and  (a)d  the  specific  rotatory  power, 
which  has  been  determined  for  all  well-known  optically  active 
substances  ;  w  can  easily,  therefore,  be  calculated.  The  specific 
rotatory  powers  of  a  few  of  the  most  important  optically  active 
substances  are  as  follows  : 


Cane-sugar,  (a)d=  +  73.8° 
Milk-sugar  "  =  +  59.3° 
Dextrin"  "  =+130.8° 


Levulose  (a)d=— 106° 

Egg-albumin         "   =-   33.5° 
Serum-albumin     "   =  -   56° 


Dextrose  "    =  +   56°       I   Gelatin  =-130°." 

Other  tests  for  the  presence  of  dextrose  are  Pavy's  modification 
of  Fehling's,  Moore's,  picric  acid,  and  phenylhydrazin ;  for  the 
methods  of  their  use  the  reader  is  referred  to  special  manuals  on 
chemistry  and  urine-analysis. 

Fermentations  of  Dextrose. — Dextrose  undergoes  various  fer- 
mentations :  (1)  Alcoholic ;  (2)  Lactic  ;  and  (3)  Butyric. 

1.  Alcoholic  Fermentation. — In  alcoholic  fermentation,  under 
the  influence  of  yeast,  the  dextrose  is  decomposed  and  ethyl 
alcohol  and  carbonic  anhydrid  are  produced  (C6H12O6  =  2C2H6O  -f 
2CO2).'  This  process  is  at  the  height  of  its  activity  when  the 
temperature  is  25°  C. ;  when  above  45°  C.  or  below  5°  C.  it 
ceases.  When  sugar  is  present  in  the  solution  to  the  extent  of 
more  than  15  per  cent,  the  process  of  fermentation  will  be 


92  CARBOHYDRATES. 

arrested  by  the  alcohol  produced,  before  all  the  sugar  has  been 
decomposed. 

2.  Lactic  Fermentation. — When  milk  sours,  the  sugar  which  it 
contains  is  converted  into  lactic  acid,  constituting  the  lactic  fer- 
mentation : 

C12H220U  +  H20  ----  4  C3H603 

Lactose.  Water.  Lactic  acid. 

This  fermentation  is  not  confined  to  milk-sugar,  but  may  occur 
also  with  dextrose.  The  change  is  brought  about  by  the  presence 
of  specific  micro-organisms.  It  is  stated  that  there  exists  also  in 
the  mucous  membrane  of  the  stomach  an  enzyme  which  can  change 
lactose,  and  possibly  dextrose,  into  lactic  acid. 

3.  Butyric  Fermentation. — When  the  lactic  fermentation  is  con- 
tinued for  some  time  it  is  liable  to  pass  into  the  butyric.    This 
change  is  due  to  the  action  of  a  ferment  (organized)   upon  the 
lactic  acid.     In  the  change,  hydrogen  and  carbonic  anhydrid  are 
given  off. 

4C3H603  «  2C4H802  +  4C02  +  4H2 

Lactic  acid.          Butyric  acid.       Carbonic    Hydrogen, 
anhydrid. 

The  optimum  (most  favorable)  temperature  for  the  lactic  and 
butyric  fermentations  is  from  35°  C.  to  40°  C.  When  the  diet 
consists  largely  of  carbohydrates  both  these  fermentations  may 
occur  in  the  alimentary  canal. 

Levulose  (left-rotating  sugar,  fruit-sugar,  or  mucin-sugar)  is 
found  in  many  fruits  and  in  honey,  and  occurs  in  small  quantity 
in  blood,  urine,  and  muscle.  It  is  crystallizable,  but  with  diffi- 
culty. When  cane-sugar  is  treated  with  dilute  mineral  acids  it  is 
decomposed  into  equal  parts  of  dextrose  and  levulose.  Cane- 
sugar  has  a  dextrorotatory  action  on  polarized  light,  but  when 
changed  by  the  acid  the  solution  becomes  levorotatory,  the  levo- 
rotatory  power  of  the  levulose  being  greater  than  the  dextro- 
rotatory power  of  the  dextrose,  and  the  cane-sugar  is  said  to  be 
"  inverted  ;"  hence  the  mixture  of  dextrose  and  levulose  is  some- 
times spoken  of  as  "  invert-sugar."  As  will  be  seen  in  the  con- 
sideration of  cane-sugar,  "  inversion"  takes  place  in  the  alimentary 
canal.  Although  in  many  respects  levulose  is  very  similar  to 
dextrose,  still  its  action  on  polarized  light  serves  to  distinguish 
the  two. 

Galactose. — When  lactose  is  boiled  with  dilute  mineral  acids 
it  is  changed  into  dextrose  and  galactose : 

C^O,,  +  H20  =  C6H1206  +  C6H1206 

Lactose.  Water.         Dextrose.  Galactose. 

A  similar  change  takes  place  under  the  influence  of  certain 
enzymes. 


DISACCHARIDS  OR  SACCHAROSES.  93 

Inosit  or  muscle-sugar  has  been  found  in  the  muscles,  lungs, 
liver,  spleen,  kidneys,  and  brain,  and  pathologically  in  urine.  It 
occurs  also  in  beans  and  grape-juice.  Because  of  its  sweet  taste 
and  its  chemical  composition  it  was  formerly  regarded  as  a  carbo- 
hydrate, but  as  it  has  no  rotatory  action  on  polarized  light,  does  not 
reduce  metallic  salts,  and  does  not  undergo  the  alcoholic  fermen- 
tation, it  is  now  regarded  as  belonging  te  the  aromatic  series,  and 
not  as  being  a  carbohydrate. 

Disaccharids  or  Saccharoses. — The  chemical  formula 
representing  this  group  is  C12H22On.  They  are  regarded  as  a  con- 
densation-product of  two  molecules  of  the  monosaccharids,  in  which 
a  molecule  of  water  is  lost.  This  may  be  expressed  as  follows : 

C6H1206  +  C6H1206  -  C^H^A,  +  H20 

Mono-  Mono-  Disaccharid.        Water, 

saccharid.          saccharid. 

This  process  is  known  as  reversion. 

The  members  of  this  group  which  are  of  physiologic  impor- 
tance are  Cane-sugar,  Lactose,  Maltose,  and  Isomaltose. 

Cane-sugar  or  Saccharose. — This  sugar  is  not  found  in  the  human 
body,  but  it  nevertheless  plays  an  important  part  in  the  food  of 
man.  It  occurs  in  sugar-cane,  beet-root,  and  sugar-maple.  It 
does  not  reduce  metallic  salts,  is  soluble  in  water,  dextrorotatory, 
and  does  not  undergo  alcoholic,  but  does  readily  undergo  lactic 
fermentation  in  presence  of  sour  milk  to  which  zinc  oxid  is  added 
to  fix  the  acid  as  formed.  One  of  the  interesting  facts  connected 
with  cane-sugar  is  its  property  of  "  inversion,"  which  consists  in 
its  decomposition  into  equal  parts  of  dextrose  and  levulose,  and 
to  this  mixture  the  name  of  "  invert-sugar"  has  been  given.  This 
change  is  represented  chemically  as  follows : 

C^E^Ai  +  H20  =  C6H1206  -f-  C6H1206 

Cane-sugar.       Water.         Dextrose.         Levulose. 

and  may  be  produced  by  the  action  of  acid,  as  has  been  described 
under  Levulose.  It  takes  place  also  in  the  small  intestine 
under  the  influence  of  an  enzyme  of  the  intestinal  juice,  namely, 
invertin.  A  similar  inversion  takes  place  in  lactose  and  maltose  ; 
thus  maltose  +  water  =  dextrose  4-  dextrose ;  and  lactose  +  water 
=  dextrose  -f  galactose.  Invertin  exists  also  in  yeast,  in  wrhich  it 
has  the  same  power  as  in  the  intestinal  juice. 

Cane-sugar  cannot  be  taken  up  as  such  by  the  blood,  and  when 
injected  into  an  animal  it  is  eliminated  unaltered  in  the  urine. 
When  taken  in  as  food  it  is  absorbed,  not  as  cane-sugar,  but  as 
invert-sugar,  into  which  it  has  been  changed.  T^his  inversion  is 
most  pronounced  in  the  small  intestine ;  it  is  claimed  that  it  may 
take  place  also  in  the  stomach,  and  that  there  exists  in  the  gastric 
juice  an  enzyme  which  has  this  power. 


94  CARBOHYDRATES. 

Lactose  (milk-sugar,  sugar  of  milk)  is  found  only  in  milk, 
although  it  may  occur  in  the  urine  of  lying-in  women  and  of  suck- 
lings during  the  early  days  of  lactation.  It  is  crystallizable,  less 
soluble  in  water  than  dextrose,  and  insoluble  in  alcohol.  It  is 
dextrorotatory,  its  power  in  this  respect  being  the  same  as  that 
of  dextrose.  As  above  noted  in  speaking  of  galactose,  lactose  is 
changed  into  equal  parts  of  galactose  and  dextrose  by  boiling  it 
with  dilute  mineral  acids. 

Lactose  by  itself  does  not  undergo  alcoholic  fermentation  with 
yeast,  but  an  alcoholic  fermentation  does  take  place  in  milk,  as 
when  mare's  milk  is  used  for  the  preparation  of  kumyss  and 
kephir.  This  fermentation  is  due  to  special  ferments,  the  nature 
of  which  is  not  fully  understood.  In  Russia  kephir  ferment  may 
be  purchased.  Lactose  readily  undergoes  the  lactic  fermentation 
(see  Lactic  Fermentation,  p.  92).  It  is  this  change  which  takes 
place  in  the  souring  of  milk  due  to  the  action  of  certain  micro- 
organisms. The  character  of  the  change  in  the  case  of  lactose  is 
the  same  as  in  dextrose  and  saccharose.  Lactose  injected  into  the 
blood  is  eliminated  by  the  urine,  as  are  saccharose  and  maltose, 
and  like  them  must  therefore  be  changed  in  the  alimentary  canal 
during  the  process  of  absorption.  This  conversion,  which  is  into 
dextrose  and  galactose,  takes  place  under  the  influence  of  the  sugar- 
splitting  enzyme,  lactase  (p.  119). 

Maltose. — When  starch-paste  or  glycogen  is  treated  with  saliva, 
maltose  is  the  principal  sugar  formed ;  prolonged  treatment  with 
pancreatic  juice  will  produce,  besides  the  maltose,  some  dextrose. 
Although  pancreatic  juice,  on  the  one  hand,  acts  in  this  manner, 
still  the  tissue  of  the  small  intestine  or  an  extract  of  it  has  but 
slight  action  on  the  paste.  On  the  other  hand,  the  pancreatic  juice 
rapidly  changes  maltose  into  dextrose.  Maltose,  like  cane-sugar, 
injected  into  the  blood  is  eliminated  as  maltose  in  the  urine.  From 
this  fact  it  would  appear  that  maltose  is  not  absorbed  as  such  in 
the  intestine,  but  as  dextrose.  Recent  researches  show  the  presence 
in  the  succus  entericus  of  lambs,  and  in  the  mucous  membrane  of 
the  jejunum  of  dogs  and  new-born  children,  of  an  enzyme  glucase 
which  changes  maltose  into  glucose,  so  that  the  conversion  of  the 
maltose  may  take  place  both  in  the  cavity  of  the  intestine  and 
while  it  is  passing  through  the  intestinal  walls.  The  action  of 
pancreatic  juice  on  starch  in  the  intestine  will  be  further  discussed 
in  the  consideration  of  the  enzymes  of  this  fluid. 

Maltose  is  soluble  in  water,  but  it  is  less  soluble  in  alcohol  than 
dextrose.  It  is  crystallizable,  dextrorotatory,  and  reduces  metallic 
salts.  Maltose  is  distinguished  from  dextrose  (1)  by  the  difference 
in  its  rotatory  power  on  polarized  light,  that  of  maltose  being 
greater;  (2)  by  having  a  less  reducing  power,  as  when  boiled 
with  Fehling's  solution  only  two-thirds  as  much  cuprous  oxide 
is  separated  out  with  maltose  as  with  dextrose ;  (3)  by  Barfoed's 
reagent,  which,  consisting  of  a  solution  of  cupric  acetate  in  water 


POLYSACCHARIDS  OR  AMYLOSES.  95 

to  which  acetic  acid  has  been  added,  is  reduced  by  dextrose,  but 
not  by  maltose. 

Isomaltose. — When  starch  is  acted  on  by  any  of  the  enzymes 
which  produce  maltose  isomaltose  is  also  formed ;  unlike  maltose, 
it  is  not  directly  fermentable  by  yeast.  It  is  very  soluble  in  water, 
and  is  sweet  in  taste.  It  occurs  in  small  quantity  in  the  urine. 

Polysaccharids  or  Amyloses.— The  formula  of  this  group 

is  (C6H1005X, 

The  exact  formula  is  not  determined.  Chemists  agree  that  it 
is  not  C6H10O5,  but  some  multiple  of  this,  as  indicated  by  "  n"  and 
that  "  n"  is  not  less  than  five.  The  members  of  the  group  are  : 
Starch,  Amylodextrin,  Erythrodextrin,  Achroodextrin,  Maltodex- 
trin,  Glycogen,  and  Cellulose. 

Starch. — Starch  is  not  found  in  the  human  body  except  when 
it  is  taken  in  as  food.  It  is  very  abundant  in  vegetable  food.  In- 
deed, it  is  said  that  starch  exists  in  every  chlorophyll-containing 
plant  at  some  period  of  its  existence.  Starch  is  a  substance  of 
great  interest,  from  the  fact  that  it  is  the  first  organic  substance 
produced  by  vegetables  from  inorganic  matter.  Animals  have 
not  the  power  to  produce  organic  substances  directly  from  mem- 
bers of  the  inorganic  kingdom,  but  plants  have  this  power,  and 
they  exercise  it,  and  from  the  organic  materials  thus  produced 
animals  are  nourished.  Animals  may  change  the  organic  matter 
from  one  form  to  another,  as  starch  to  sugar,  but  were  inorganic 
substances  alone  supplied  to  animals  they  would  starve. 

The  inorganic  substances  out  of  which  the  plant  forms  the 
starch  are  carbonic  acid  and  water,  these  being  taken  from  the 
atmosphere  and  the  soil.  This  process  is  represented  by  the  fol- 
lowing formula : 

(6C02  +  5H20)n  =  (C6H1005)»  +  On 

Carbonic  acid.       Water.  Starch.  Oxygen. 

That  is,  the  carbonic  acid  and  the  water  are  decomposed,  the  car- 
bon and  hydrogen,  with  some  of  the  oxygen,  unite  and  form 
starch,  while  the  rest  of  the  oxygen  is  set  free.  To  bring  about 
this  change  there  must  be  present  solar  light  and  the  green  color- 
ing-matter, chlorophyll.  If  chlorophyll  is  absent,  this  change 
does  not  take  place,  nor  does  it  when  solar  light  is  absent. 

Starch  exists  in  plants  in  the  form  of  grains,  known  as 
"  starch-grains"  or  "  starch-granules"  (Fig.  83).  They  present  a 
characteristic  appearance  under  the  microscope  by  which  they 
may  at  once  be  recognized.  Each  granule  presents  a  number 
of  concentric  markings  and  varies  in  size  and  shape  in  different 
plants ;  by  these  points  of  difference  the  plant  from  which  the 
granules  are  derived  may  be  identified.  This  fact  is  made  use  of 
in  detecting  adulterations,  in  which  cheaper  kinds  of  starch  are 
mixed  with  more  expensive  kinds  and  sold  for  the  latter  at  a 


96 


CARBOHYDRATES. 


higher  price.  The  markings  are  caused  by  the  arrangement  of 
the  material  composing  the  granule  in  alternate  layers  of  cellulose 
and  granulose. 

Quantity  of  Starch. — The  quantity  of  starch  (percentage)  in 
the  following  food-plants  is 

Sweet  potato    . 16.05 

Potato 20.00 

Beans 33.00 

Peas       49.30 

Wheat 57.88 

Oats 60.59 

Eye 64.65 

Indian  corn 67.55 

Kice  ...'..• 88.65 

The  presence  of  starch  is  determined  by  the  addition  of  a  little 
tincture  of  iodin,  which  gives  a  blue  color.  This  reaction  is  due 

to  the  granulose,  and  not  to  the  cel- 
lulose. Starch  cellulose  differs  in 
some  respects  from  ordinary  cellu- 
lose, as  is  demonstrated  by  its  solu- 
bility in  some  reagents  which  do  not 
dissolve  the  latter* 

Starch  is  insoluble  in  cold  water. 
When  boiling  water  is  added  to  it  in 
an  amount  twenty  times  its  weight 
the  granules  swell  and  burst,  and 
there  is  formed  a  gelatinous  mass 
which  is  called  "  starch-paste."  This 
paste  will  respond  to  the  iodin  test, 
showing  it  to  be,  principally  at  least, 
granulose.  If  the  amount  of  water 
added  should  be  one  hundred  times  the  weight  of  the  starch,  a 
solution  of  granulose  is  made,  the  insoluble  cellulose  falling  to  the 
bottom  of  the  vessel.  This  starch  solution  will  likewise  respond 
to  the  iodin  test. 

Amylodextrin  (Soluble  Starch,  Amidulin). — When  starch-paste, 
produced  in  the  manner  above  described,  is  heated  to  a  temperature 
of  40°  C.  on  a  water-bath,  and  saliva  is  then  added,  the  paste 
changes  from  a  gelatinous  to  a  watery  condition,  and  in  this  fluid 
soluble  starch  now  exists.  This  soluble  starch  gives  also  a  blue 
color  with  iodin.  It  filters  readily,  whereas  starch-paste,  even  in 
dilute  solution,  filters  with  difficulty.  Soluble  starch  is  dextro- 
rotatory— that  is,  it  rotates  the  ray  of  polarized  light  to  the  right. 
This  substance  is  the  first  product  of  the  conversion  of  starch  into 
sugar  by  saliva ;  and  if  the  action  is  not  stopped,  as  it  may  be  by 
boiling,  the  stage  of  soluble  starch  is  only  a  temporary  one,  it  pass- 
ing quickly  into  that  of  dextrin.  As  will  be  seen  hereafter,  the 
ingredient  of  the  saliva  that  changes  starch  into  soluble  starch  is 


FIG.  83. — Starch-grains. 


POLYSACCHAEIDS  OR  AMYLOSES.  97 

an  enzyme — ptyalin — the  action  being  one  of  hydrolysis.  Pancreatic 
juice  produces  the  same  change  as  does  saliva ;  and  as  the  action 
of  saliva  is  due  to  the  enzyme  ptyalin,  so  is  the  action  of  pancreatic 
juice  due  to  an  enzyme,  amylopsin. 

Erythrodextrin. — If  the  action  of  either  of  these  enzymes  upon 
starch  is  not  arrested  in  the  soluble-starch  stage,  erythrodextrin 
is  formed.  The  blue  color  caused  by  the  action  of iodin  on  starch 
gradually  changes  into  violet,  reddish  violet,  and  then  to  reddish 
brown  as  the  starch  gradually  changes  to  erythrodextrin.  This 
reddish-brown  color  produced  by  iodin  is  the  test  for  erythro- 
dextrin. 

Achrobdextrin. — If  the  action  of  these  enzymes  is  continued, 
a  still  further  change  in  the  starch  takes  place.  It  passes  into  the 
condition  of  achroodextrin,  and  iodin  fails  to  produce  any  color. 
A  further  change  into  maltose  follows  the  formation  of  achroo- 
dextrin. In  the  action  of  these  enzymes  upon  starch  outside  the 
body  the  first  product  is  a  mixture  of  dextrin  with  the  sugar,  but 
within  the  body  there  is  little  doubt  that  all  the  starch  is  converted 
into  sugar,  and  as  such  is  absorbed.  If  starch  is  treated  with 
boiling  dilute  acids  instead  of  with  these  enzymes,  the  changes 
just  described  take  place  with  far  greater  rapidity,  and  dextrose 
results. 

Maltodextrin. — If  diastase,  the  enzyme  contained  in  malt 
extract,  is  used  instead  of  saliva  or  pancreatic  juice,  maltodextrin 
is  formed ;  and  indeed  it  is  not  certain  that  the  latter  substance  is 
not  formed  in  addition  to  the  erythrodextrin  and  achroodextrin 
when  saliva  and  pancreatic  juice  are  employed.  Maltodextrin 
differs  from  the  dextrins  already  described  in  being  more  soluble 
in  alcohol,  in  being  diffusible,  and  in  responding  to  Fehling's  test. 
It  also  passes  over  into  maltose  by  the  continued  action  of  the 
diastase. 

Glycogen. — The  similarity  between  glycogen  and  starch  has  led 
to  the  term  "animal  starch"  being  applied  to  the  former.  Glycogen 
was  first  discovered  in  the  liver,  where  it  is  normally  found  to  the 
amount  of  between  1.5  and  4  per  cent,  of  the  weight  of  the  organ, 
which  may  in  man  be  increased  to  10  per  cent.  It  also  exists  in 
muscles  to  the  amount  of  from  0.5  to  0.9  per  cent.,  and  it  is 
estimated  that  all  the  muscles  of  the  body  contain  as  much  glyco- 
gen as  does  the  liver.  It  occurs  also  in  the  integument  and  the 
mucous  membranes  of  the  human  embryo,  in  the  placenta  and 
the  amnion,  in  white  blood-corpuscles  and  in  pus-corpuscles,  in 
oysters  and  in  other  mollusca.  For  purposes  of  study  it  is  usu- 
ally obtained  from  the  liver  of  an  animal  (a  rabbit  or  a  dog),  in 
which  it  is  stored  up  in  amorphous  granules  around  the  nuclei  of 
the  liver-cells.  Glycogen  is  soluble  in  water,  and  with  iodin  gives 
a  port-wine  color.  This  color  does  not  distinguish  it  from  erythro- 
dextrin ;  but  when  it  exists  pure,  as  ordinarily  it  does  not,  it  is 
7 


98  CARBOHYDRATES. 

precipitated  by  60  per  cent,  alcohol,  while  the  dextrins  are  not 
precipitated.  Watery  solutions  are  dextrorotatory. 

In  general  it  may  be  said  that  the  action  of  the  enzymes  and 
of  boiling  acids  upon  glycogen  is  the  same  as  upon  starch.  The 
glycogen  of  the  liver  becomes  converted,  by  physiologic  processes, 
into  liver-sugar,  which  is  regarded  as  identical  with  dextrose.  In 
this  process  probably  no  maltose  is  formed,  such  as  occurs  in  the 
artificial  hydrolysis  already  described.  This  difference  would 
seem  to  indicate  that  in  the  liver-cells  there  is  no  enzyme  to 
which  this  action  can  be  attributed ;  for,  so  far  as  can  be  judged, 
most  enzymes  produce  maltose,  and  not  dextrose,  and  up  to  the 
present  time  no  dextrose-producing  enzyme  has  been  obtained 
from  the  liver. 

Cellulose. — Nowhere  in  the  animal  body  is  cellulose  found,  but 
it  exists  in  many  of  the  vegetable  alimentary  principles  upon 
which  man  relies  for  his  nutrition.  As  has  already  been  stated, 
it  is  a  constituent  of  the  starch-granule,  and  so  covers  the  granulose 
that  the  digestive  fluids  cannot  reach  it.  When  starch  is  boiled 
the  granules  burst,  and  thus  access  to  the  granulose  is  given.  It 
has  recently  been  suggested  that  there  is  in  the  intestinal  canal, 
formed  by  the  epithelial  cells,  an  enzyme  which  has  the  power 
of  causing  a  digestion  of  the  cellulose.  But  the  evidence  of  the 
existence  of  such  an  enzyme  is  very  meagre.  The  disappearance 
of  the  cellulose  is  probably  due  to  the  action  of  bacteria,  all  the 
products  being  unknown,  though  marsh-gas,  acetic  and  butyric 
acids  are  among  them.  This  change  takes  place  especially  when 
vegetables,  such  as  celery  and  lettuce,  and  fruits  are  eaten  whose 
cell-walls  are  tender  and  have  not  yet  become  lignified  or  woody 
in  character.  Lignin  is  the  name  applied  to  cellulose  in  this 
advanced  stage.  In  the  human  intestine  from  4  to  60  per  cent, 
of  the  cellulose  taken  in  is  dissolved.  It  doubtless  has  very  little 
nutritive  value,  but  is  regarded  as  increasing  by  its  local  action 
intestinal  peristalsis  and  keeping  the  bowels  free.  In  the  rabbit 
its  absence  from  the  food  results  in  death,  inflammation  of  the 
intestine  being  caused  thereby ;  but  if  horn-shavings,  which  are 
excreted  unchanged,  are  substituted  for  cellulose,  the  animal 
maintains  its  health.  The  cellulose  of  some  plants,  such  as 
the  date,  is  regarded  as  a  reserve  material  to  be  made  use  of  in 
germination. 

The  presence  of  cellulose  is  recognized  by  the  fact  that  when 
treated  with  strong  sulphuric  acid  it  becomes  converted  into  a  sub- 
stance that  is  colored  blue  by  iodin.  Schulze's  reagent  is  another 
test  for  its  presence.  This  test  consists  in  the  production  of  a  blue 
color  when  the  substance  is  treated  with  iodin  dissolved  to  satura- 
tion in  a  solution  of  chlorid  of  zinc  to  which  potassium  iodid  has 
been  added. 


ADIPOCERE. 


99 


THE  FATS. 

The  chemical  elements  entering  into  the  composition  of  the 
fats  are  carbon,  hydrogen,  and  oxygen.  The  fats  are  widely  dis- 
tributed throughout  the  human  body.  The  percentage  in  the  solids 
and  fluids  is  as  follows  : 


Sweat 0.001 

Vitreous  humor 0.002 

Saliva 0.02 

Lymph 0.05 

Synovia 0.06 

Liquor  amnii    ..." 0.06 

Clfc'le 0.2 

Mlcus 0.3 

Blood 0.4 

BUe 1.4 

Milk -^:3 


Cartilage      1.3 

Bone 1.4 

Crystalline  lens 2.0 

Liver 2.4 

Muscles 3.3 

Hair 4.2 

Brain 8.0 

Nerves 22.1 

Adipose  tissue 82.7 

Marrow    .  .96.0 


Fats  are  regarded  by  chemists  as  composed  of  fatty  acids  and 
glycerin,  and  are  called  glycerids  or  glyceric  ethers.  When 
treated  with  superheated  steam  and  mineral  acids,  and  in  the 
human  body  under  the  influence  of  steapsin,  the  lipolytic  enzyme 
of  the  pancreatic  juice,  the  fats  are  decomposed  into  glycerin  and 
the  respective  fatty  acid.  This  change  is  expressed  by  the  follow- 
ing formula,  palmitin  being  taken  as  an  example : 


C3H5(O.C15H31CO)3 

Palmitin. 


3H2O  =  C3H5(OH)3 

Water.  Glycerin. 


3C15H31CO.OH 

Palmitic  acid. 


There  are  three  varieties  of  fats:  Olein,  C3H5(OC17H<33CO)3 ; 
palmitin,  C3H5(OC15H31CO)3 ;  and  stea7uTpC3H5(OC17H35CO)3. 
These  differ  in  several  particulars,  one  of  the  most  important 
being  their  melting-points :  Olein  melts  at  5°  C.  ;  palmitin,  at 
45°  C. ;  and  stearin,  at  from  53°  to  66°  C.  Their  respective  acids 
are  oleic,  palmitic,  and  stearic. 

Fats  are  characterized  by  being  insoluble  in  water,  slightly 
soluble  in  alcohol,  and  very  soluble  in  ether  and  chloroform.  All 
fats  are  mixtures  of  the  three  varieties,  the  difference  in  the  con- 
sistency of  any  given  fat  depending  upon  the  proportion  in  which 
the  neutral  fats  are  present.  Thus  in  the  more  solid  fats,  such 
as  suet,  stearin  predominates,  while  in  the  fluid  fats  it  is  olein 
which  is  in  excess.  The  latter  exists  in  human  fat  to  the  amount 
of  from  67  to  80  per  cent.  When  fats  decompose  or  become 
"  rancid/'  propionic,  acetic,  and  formic  acids  are  produced. 

Adipocere. — It  sometimes  happens  that  when  bodies  are  dis- 
interred, instead  of  being  found  in  a  condition  of  putrefaction, 
they  are  discovered  to  have  been  changed  into  adipocere  or  grave- 
wax.  This  is  a  peculiar  substance  of  a  waxy  nature,  and  consists 
of  calcium  soaps,  of  which  the  fatty  acids  are  palmitic  and  stearic. 
Acid  ammonium  soap  has  been  found  in  some  cases.  This  change 


100  THE  FATS. 

occurs  in  bodies  which  have  been  interred  in  moist  soils,  or  have 
been  in  water  for  a  considerable  time  after  death. 

Source  of  Fat  in  the  Human  Body. — Human  fat  is  de- 
rived from  the  fats,  the  carbohydrates,  and  the  proteids  of  the  food. 
In  fatty  meats,  nuts,  eggs,  milk,  and  other  foods  more  or  less  fat 
exists  as  a  constituent,  and  undoubtedly  contributes  to  the  forma- 
tion of  the  fat  of  the  body.  That  the  fat  of  the  food  can  be 
deposited  as  such  in  the  tissues  was  for  a  time  denied,  but  it  has 
been  shown  by  feeding  starved  dogs  upon  such  fatty  foods  as  rape- 
seed  oil,  linseed  oil,  or  mutton  tallow,  that  they  will  not  only  take 
on  fat,  but  that  some  of  the  kind  of  fat  which  enters  into  their 
food  is  deposited  as  such  in  their  tissues.  Food  containing  starch 
and  sugar  is  also  fattening  in  its  nature,  and  persons  who  have  an 
excess  of  fat  are  placed  upon  a  diet  containing  a  minimum  of  these 
ingredients.  Herbivorous  animals — the  cow,  for  instance — rely 
entirely  upon  vegetable  food  for  their  support,  and  it  is  the  carbo- 
hydrates which  this  contains  that  are  converted  into  the  fat  of 
their  milk  and  that  which  covers  their  muscles.  It  is  doubtless 
from  the  carbohydrates  that  most  of  the  fat  is  produced.  That 
proteid  food  will  also  produce  fat  is  shown  by  the  amount  of  the 
latter  which  carnivorous  animals  put  on. 

Offices  of  Fat. — The  offices  which  fat  subserves  in  the  human 
body  are  manifold  :  (1)  It  protects  the  underlying  parts  from  in- 
jury, as  in  the  palm  of  the  hand  and  the  sole  of  the  foot ;  (2)  it 
serves  as  a  lubricator,  as  in  the  sebaceous  matter  poured  out  upon 
the  skin,  which  it  keeps  soft  and  pliable  ;  (3)  it  acts  as  a  non- 
conductor of  heat,  aiding  in  the  retention  within  the  body  of  the 
vital  heat  which  would  otherwise  be  lost  so  rapidly  as  to  produce 
injurious  results;  (4)  it  serves  as  a  reservoir  when  the  supply  of 
food  is  cut  off  or  diminished ;  thus  in  wasting  diseases  the  fat 
deposited  in  various  parts  of  the  body  is  absorbed  and  contributes 
to  its  nutrition ;  (5)  it  is  a  source  of  energy  and  of  heat  through 
its  oxidation,  the  final  products  of  which  are  CO2  and  H2O. 

Important  properties  of  fats,  besides  those  already  men- 
tioned, which  deserve  special  consideration,  are  two — that  of  form- 
ing a  soap  and  that  of  forming  an  emulsion. 

Saponification. — Fats  are  saponifiable — i.  e.,  capable  of  being 
converted  into  a  soap.  Thus  when  heated  with  a  caustic  alkali 
the  fat  is  split  up  as  already  described,  into  glycerin  and  a  fatty 
acid,  and  the  latter  unites  with  the  base,  the  compound  resulting 
being  a  soap.  Thus  if  palmitin  and  potassium  hydrate  are  the 
fat  and  alkali  used,  the  product  is  a  soap  whose  chemical  composi- 
tion is  potassium  palmitate.  This  is  expressed  in  the  following 
formula : 

C3H5(O.C15H31CO)3  +  3KHO          C3H5(OH)3  +  3C15H31CO.OK 

Talmitin.  Potassium  hydrate.  Glycerin.  Potassium  palmitate. 


CHOLESTERIN.  101 


In  like  manner  stearin  would  form  i  ^teaite^  and  'oljein  an 
oleate.  The  sodium  soaps  are  "hard/7  a^nd  those  of  potassium  are 
"  soft/7  In  the  discussion  of  intestinal  digestion  it  yviti  ha.  seoil  thitt 
the  process  of  saponification  takes  place  in  the  small  intestine,  and 
that  the  soap  there  formed  aids  in  the  important  functions  of  that 
portion  of  the  alimentary  canal  (p.  236). 

Emulsification.  —  Besides  being  saponifiable,  fats  are  also  emul- 
sifiable  —  capable  of  forming  an  emulsion.  If  oil  and  water  are 
poured  into  a  test-tube,  they  will  at  once  separate,  the  oil  floating 
on  the  water.  If  the  mouth  of  the  tube  is  closed  by  the  thumb 
and  the  tube  firmly  shaken,  the  oil  and  water  will  form  a  milky 
mixture,  but  will  separate  again  when  the  agitation  ceases  ;  if  a 
small  amount  of  an  alkali  is  added  and  the  tube  is  again  shaken, 
separation  will  not  take  place  as  before,  but  the  milky  appear- 
ance will  continue  for  some  considerable  time.  If  a  drop  of  the 
mixture  is  placed  under  the  microscope,  it  will  be  found  that  the 
oil-globules  have  been  broken  up  into  an  exceedingly  fine  state  of 
subdivision,  some  of  the  particles  being  too  small  to  measure  even 
with  a  very  high  magnifying  power.  This  more  or  less  permanent 
subdivision  and  suspension  of  the  oil-globules  constitutes  an  emul- 
sion. The  change  is  not  a  chemical  one,  but  purely  physical.  A 
similar  process  takes  place  in  the  small  intestine  during  intestinal 
digestion  (p.  237)  and  is  regarded  by  some  as  a  necessary  prelimi- 
nary to  the  absorption  of  fat  (p.  261). 

The  fat  in  milk  is  in  an  emulsified  condition  ;  consequently 
milk  may  be  regarded  as  a  natural  emulsion. 

lecithin.  —  This  substance  may  be  regarded  as  a  fat,  and  from 
the  fact  that  it  contains  phosphorus  it  has  been  spoken  of  as  "  phos- 
phorized  fat.v  Its  formula  is  C42H84NPO9.  It  is  decomposable 
into  glycerin,  stearic  acid,  phosphoric  acid,  and  an  alkaloid, 
cholin. 

Lecithin  occurs  in  the  brain  and  other  nervous  tissues,  consid- 
ered by  some  authorities  as  here  produced  by  decomposition  of 
protagon,  in  yolk  of  eggs,  blood-corpuscles,  semen,  bile,  and  milk. 
It  is  also  one  of  the  constituents  of  protoplasm. 

Cholesterin.  —  This  substance  bears  some  resemblance  to  the 
fats  in  that  it  is  insoluble  in  water,  but  soluble  in  ether,  hot  alco- 
hol, and  chloroform.  It  is  a  constituent  of  protoplasm,  and  is  also 
found  in  blood-corpuscles,  bile,  serum,  and  white  substance  of 
Schwann.  In  the  blood  it  is  in  combination  with  oleic  and  pal- 
mitic acids.  It  forms  esters  with  fatty  acids,  and  as  such  exists 
in  the  fatty  secretions  of  the  skin.  Lanolin,  the  fat  obtained  from 
sheeps'  wool,  is  said  to  be  rich  in  esters,  and  these  are  very  resist- 
ant to  the  action  of  bacteria. 


102 


PROTEIDS. 


*  ^PROTEIDS. 

.'•  \  33te^s6- ingr^p  ents/a-re  the  most  important  constituents  of  mus- 
cles, glands,  nervous  tissue,  and  blood ;  indeed,  it  has  been  said 
of  them  that  none  of  the  phenomena  of  life  occurs  without  their 
presence.  Of  them  Gamgee  says :  "  They  are  highly  complex, 
and,  for  the  most  part,  uncrystallizable  compounds  of  carbon, 
hydrogen,  oxygen,  nitrogen,  and  sulphur  (phosphorus  is  also  some- 
times present),  occurring  in  a  solid,  viscous  condition,  or  in  solu- 
tion in  nearly  all  the  solids  and  liquids  of  the  organism.  The 
different  members  of  the  group  present  differences  in  physical, 
and  to  a  certain  extent  even  in  chemical  properties.  They  all  pos- 
sess, however,  certain  common  chemical  reactions,  and  are  united 
by  a  close  genetic  relationship." 

Their  percentage-composition  is  as  follows  : 

Carbon .  50      to    55 

Nitrogen 15       "18 

Hydrogen 6.9   "       7.3 

Oxygen 20       "     23.5 

Sulphur 0.3   "      2 


qu£ 
chl 


When  proteids  are  burned  there  is  found  in  the  ash  a  certain 
uantity  of  salts ;  from  the  ignition  of  egg-albumin,  for  instance, 
chlorids  of  sodium  and  potassium  result,  and  salts  of  calcium, 
magnesium,  and  iron.  It  is  still  undecided  whether  these  salts 
are  integral  parts  of  proteids  or  impurities,  probably  the  latter. 

The  percentage  of  proteids  in  some  of  the  solids  and  liquids 
of  the  body,  and  their  wide  distribution,  are  shown  by  the  follow- 
ing table  : 


Cerebrospinal  fluid .......  0.09 

Aqueous  humor 0.14 

Liquor  amnii 0.70 

Intestinal  juice 0.95 

Pericardia!  fluid 2.36 

Lymph 2.46 

Pancreatic  juice 3.33 

Synovia 3.91 

Milk 3.94 


Chyle 4.09 

Blood 8.56 

Spinal  cord 7.49 

Brain 8.63 

Liver    ...•..; 11.64 

Thymus 12.29 

Muscle 16.18 

Tunica  media  of  arteries  ....  27.38 

Crystalline  lens 38.30 


Various  attempts  have  been  made  to  ascertain  the  constitution 
of  the  proteids  and  give  a  formula  for  them,  but  the  differences 
in  the  results  obtained  by  equally  competent  chemists  have 
been  so  great  that  practically  nothing  worthy  of  quoting  is  on 
record.  There  is  no  doubt,  however,  that  the  molecules  are  very 
large. 

General  Properties  of  Proteids. — All  are  insoluble  in 
alcohol  and  ether.  They  are  also  said  to  be  soluble  with  the  aid 
of  heat  in  concentrated  mineral  acids  and  caustic  alkalies ;  but 
inasmuch  as  this  is  accompanied  with  decompositien  of  the  pro- 


COLOR-REACTIONS.  103 

teids  it  is  a  question  whether  it  can  be  regarded  as  a  true  solu- 
tion. 

Action  on  Polarised  I/ight. — All  proteids  are  levorotatory 
(see  p.  89),  but  the  degree  of  rotation  varies  considerably.  The 
following  table  gives  the  specific  rotatory  power  of  several  of  the 
proteids : 

Proteid.  Value  of  (d)d. 

Serum-albumin —  56°      to   -  68° 

Egg-albumin -  35.5°   "    -  38.08° 

Lactalbumin -  36°      "    -  37° 

Serum-globulin -  59.75° 

Fibrinogen -  43° 

Alkali-albumin -  62.2° 

Syntonin  (from  myosin) —  72° 

Casein  (dissolved  in  MgSO4  solution)   ....  -80° 

Various  proteoses —  70°      to   —  80° 

Color-reactions. — Certain  color-changes  which  take  place 
when  proteids  are  treated  with  various  reagents  have  been  made 
use  of  to  detect  their  presence  or  absence.  Although  chemists 
have  determined  the  elements  which  go  to  make  up  proteids,  they 
have  not  as  yet  determined  their  constitution.  They  have  ascer- 
tained that  proteids  undergo  changes  or  decomposition  in  the  body, 
as  a  result  of  which  carbonic  acid,  water,  and  urea  are  finally 
formed,  and  that  there  are  various  intermediate  products,  such  as 
leucin,  creatin,  uric  acid,  and  ammonia.  It  has  also  been  deter- 
mined that  by  chemical  means  proteids  can  be  decomposed  into  a 
great  variety  of  substances :  some  of  these  are  ammonia,  carbonic 
acid,  amins,  leucin,  and  aromatic  compounds.  Of  this  last  class, 
the  aromatic  compounds,  there  are  three  groups:  1.  The  phenol 
group,  including  tyrosin,  phenol,  and  cresol ;  2.  The  phenyl  group, 
including  phenylacetic  and  phenylpropionic  acids ;  and  3.  The 
indol  group,  in  which  are  indol  and  skatol.  It  is  upon  this  class 
of  substances,  the  aromatic  compounds  or  radicles,  that  the  color- 
reactions  of  proteids  depend. 

Xanthoproteic  Reaction. — When  a  solution  of  proteid,  to  which  a 
few  drops  of  nitric  acid  have  been  added,  is  boiled,  it  becomes  yel- 
low, and  if  ammonia  is  added  the  yellow  color  changes  to  orange. 

Millon's  Reaction. — Proteids  when  heated  with  Millon's  reagent 
give  a  white  precipitate  which  becomes  brick  red  on  cooling.  This 
reagent  is  prepared  by  dissolving  mercury  in  nitric  acid  and  add- 
ing water.  The  precipitate  which  forms  is  allowed  to  settle,  and 
the  fluid  is  the  reagent.  Very  small  amounts  of  proteids  give  the 
red  color  without  the  precipitate. 

Piotrowski's  or  Biuret  Reaction. — When  many  proteids  are  mixed 
with  an  excess  of  concentrated  solution  of  sodium  hydrate  and 
one  or  two  drops  of  a  dilute  solution  of  cupric  sulphate,  a  violet 
color  is  produced  which  becomes  deeper  on  boiling  ;  with  peptones 
and  proteoses  the  color  produced  is  rose  red.  Biuret  is  the  substance 


104  PROTEIDS. 

formed  when  urea  is  heated,  ammonia  being  given  off  in  the  process. 
The  following  formula  expresses  the  change  which  takes  place  : 

2CON2H4  -  NH3  =  C2O2N3H5 

Urea.          Ammonia.          Biuret. 

Since  the  rose-red  color  is  produced  by  biuret,  the  reaction  is  also 
called  by  this  name. 

Crystallization. — While  it  is  true  that  proteids  as  a  class 
are  not  crystallizable,  or  perhaps  it  would  be  more  correct  to  say 
have  never  been  crystallized,  still  there  are  exceptions  to  this  rule, 
inasmuch  as  crystals  of  globulin  or  vitellin  have  been  seen  in  the 
aleurone  grains  of  seeds  and  in  the  yolk  of  the  egg  of  fishes  and 
amphibians.  Egg-albumin,  serum^albumin,  and  caseinogen  have 
also  been  made  to  crystallize.  This  may  be  demonstrated  in  the 
following  way :  To  a  solution  of  egg-albumin,  white  of  egg,  add 
half  its  volume  of  a  saturated  solution  of  sodium  sulphate,  pre- 
cipitating the  globulin,  which  is  removed  by  filtration.  In  the 
filtrate,  exposed  to  the  air  for  some  days,  during  which  evapora- 
tion takes  place,  minute  spheroidal  globules  and  needles  will  form, 
which  are  the  crystals  of  the  proteid.  Acetic  acid  hastens  the 
crystallization  and  produces  better  crystals. 

Non-diffiisibility. — As  a  class,  proteids  are  not  diffusible ; 
to  this  rule  peptones  are  the  exception.  In  order  that  this  prop- 
erty of  proteids  may  be  understood,  it  will  be  advantageous  to  the 
student  to  describe  the  processes  of  diffusion  and  osmosis.  If  a 
solution  of  common  salt  is  placed  in  a  vessel  and  water  is  care- 
fully poured  on  the  surface  of  the  salt  solution,  the  salt  will  pass 
into  the  water,  and  in  a  short  time  the  contents  of  the  vessel  will 
be  of  the  same  composition  throughout.  This  passage  of  the  salt 
into  the  water  is  diffusion,  and  in  this  instance  the  process  takes 
place  very  quickly.  Not  so,  however,  would  be  the  case  if  a 
solution  of  albumin  was  substituted  for  the  solution  of  salt ;  the 
same  phenomenon  would  occur,  but  would  require  a  much  longer 
time.  When  liquids  are  separated  by  a  membrane  the  diffusion 
which  takes  place  through  it  is  osmosis. 

It  is  important  to  understand  osmosis  and  the  conditions  under 
which  it  takes  place,  as  without  this  knowledge  many  of  the  proc- 
esses which  occur  in  the  human  body  would  be  unintelligible ;  at 
the  same  time  it  must  be  said  that  osmosis  does  not  occupy  the 
prominent  place  it  once  did  in  explaining  phenomena  connected 
with  absorption  ;  investigations  have  shown  that  the  passage  of 
the  products  of  digestion  from  the  alimentary  canal  into  the  blood 
is  not  a  simple  diffusion  through  a  passive  membrane,  but  that 
cell-activity  must  be  largely  taken  into  account. 

Fig.  84  represents  a  jar,  A,  which  contains  distilled  water. 
Within  this,  resting  on  a  tripod,  is  an  osmometer,  an  expanded 
glass  vessel,  B,  closed  by  a  piece  of  parchment,  C,  from  the  top 


NON-DIFFUSIBILITY. 


105 


of  which  rises  a  graduated  tube.  The  osmometer  is  supposed  to 
contain  a  solution  of  some  salt ;  sulphate  of  copper,  for  instance. 
In  a  short  time  after  the  apparatus  has  been  put  in  the  condition 
described,  the  water  in  the  jar  will  become  bluish  from  the  pas- 
sage into  it  of  some  of  the  sulphate  of  copper  from  the  osmometer. 
This  outward  passage  of  the  salt  is  exosmosis.  In  the  graduated 
tube  the  fluid  in  the  osmometer  will  be  seen  to  rise  higher  and 
higher,  due  to  the  passage  of  the  distilled 
water  from  the  jar  through  the  parchment 
into  the  osmometer,  lowering  the  level  of  the 
water  in  the  jar.  This  inward  passage  con- 
stitutes endosmosis.  This  continues  until  the 
proportion  of  sulphate  of  copper  is  the  same 
in  both  jar  and  osmometer;  in  the  mean- 
time, however,  the  amount  of  water  in  the 
osmometer  is  greater  than  at  the  beginning 
of  the  experiment.  If  different  solutions 
are  used  than  those  mentioned,  the  results 
as  to  time,  amount  of  endosmosis,  etc.,  will 
vary  materially  from  those  described. 

This  subject  was  exhaustively  studied  by 
Graham,  who  objected  to  the  use  of  the 
terms  "  endosmosis  "  and  "  exosmosis,"  be- 
lieving that  there  was  in  reality  but  one 
current,  the  inward  one;  and  he  therefore 
used  only  the  terms  osmosis  and  osmotic.  In 
the  outward  passage  of  the  salt  he  held  that 
it  was  the  particles  of  salt  which  passed,  but 
not  the  water  holding  them  in  solution. 

A  second  experiment  may  be  performed 
which  illustrates  another  phase  of  osmosis. 
From  one  end  of  a  hen's  egg  the  shell  is 
to  be  carefully  removed  so  as  to  leave  the 
membrane  uninjured.  Through  the  other 

end,  into  the  interior  of  the  egg,  a  glass  tube  is  to  be  passed,  and 
the  place  at  which  it  enters  the  egg  closed  with  sealing-wax.  The 
egg  is  then  to  be  placed  in  a  wine-glass  containing  distilled  water. 
The  water  in  the  wine-glass  passes  through  the  membrane  into  the 
egg,  and  the  yolk  will  be  seen  to  rise  in  the  glass  tube  ;  at  the  same 
time  it  will  be  noted  that  the  water  in  the  wine-glass  is  diminished. 
After  a  time  a  solution  of  nitrate  of  silver  may  be  dropped  into  the 
wine-glass,  and  immediately  a  whitish  precipitate  forms,  consisting 
of  silver  chlorid.  This  is  a  proof  that  the  chlorid  of  sodium,  or 
common  salt,  which  was  a  constituent  of  the  egg,  has  passed  through 
the  membrane  into  the  water.  Other  tests  will  show  that  the  other 
salts  have  also  passed  out,  but  that  little  of  the  albumin  has  come 
through.  From  this  experiment  it  will  be  seen  that  substances  act 


FIG.   84. — Graham's  os- 
mometer. 


106  PROTEIDS. 

differently  with  reference  to  passing  through  membranes ;  those 
which  pass  through  readily  Graham  denominated  crystalloids; 
while  those  that  pass  not  at  all  or  with  difficulty,  he  called  col- 
loids, a  term  which  does  not  necessarily  imply  that  the  substances 
which  are  called  by  that  name  do  not  crystallize,  for,  as  we  have 
seen,  egg-albumin  does  crystallize,  though  salts  are  crystalloids 
and  egg-albumin  a  colloid.  This  principle  is  the  same  as 
dialysis,  or  the  separation  of  crystalloids  from  colloids  in  a 
dialyzer,  an  apparatus  constructed  like  the  osmometer,  already 
described. 

As  already  stated,  proteids,  except  proteoses  and  peptones,  are 
not  diffusible,  or,  to  put  the  statement  affirmatively,  are  colloids — 
i.  e.,  they  do  not  readily  pass  through  animal  membranes  ;  and  this 
principle  of  dialysis  is  employed  to  separate  them  from  crystal- 
loids, such  as  sugar  and  salts.  This  may  be  demonstrated  by 
putting  a  saline  solution  of  albumin  and  globulin,  as,  for  instance, 
blood-serum,  in  a  dialyzer,  the  vessel  outside  containing  distilled 
water ;  the  salts  diffuse,  leaving  the  albumin  and  globulin  behind. 
The  albumin,  being  soluble  in  water,  remains  in  solution,  and,  being 
colloid,  does  not  diffuse ;  the  globulin,  requiring  the  salts  to  hold 
it  in  solution,  is  precipitated  because  the  salts  have  diffused. 

Proteoses  are  diffusible,  but  less  so  than  peptones  ;  protoproteose 
more  than  deuteroproteose,  and  this  more  than  heteroproteose,  so 
that  the  order  of  diffusibility  would  be  peptones,  protoproteose, 
deuteroproteose,  and  heteroproteose.  It  is  to  be  borne  in  mind 
that  diffusibility  is  a  relative  term,  and  that  when  peptones  are 
said  to  be  readily  diffusible  the  idea  intended  to  be  conveyed  is, 
that  when  compared  with  other  proteids  they  exhibit  this  prop- 
erty. If,  however,  they  are  compared  with  salts,  their  diffusibility 
is  low. 

The  explanation  formerly  given  to  account  for  the  non-diffusi- 
bility  of  proteids  was  that  they  were  not  crystallizable ;  but  since 
the  discovery  of  the  fact  that  some  of  them  do  crystallize,  this 
explanation  is  abandoned,  and  for  it  is  substituted  that  of  the 
great  size  of  their  molecule.  The  molecular  weight  of  some  of 
these  proteids  has  been  determined,  and  this  confirms  the  theory 
just  enunciated:  thus  peptone,  very  diffusible,  has  a  molecular 
weight  of  400  or  less ;  protoproteose,  less  diffusible,  of  2467  to 
2600 ;  and  deuteroproteose,  still  less  diffusible,  of  3200. 

Precipitation. — As  a  class,  proteids  in  solution  are  precipit- 
able  by  certain  reagents,  of  which  the  number  is  considerable. 
Some  of  the  principal  precipitants  are  :  Nitric  acid,  picric  acid, 
acetic  acid  with  potassium  ferrocyanid,  acetic  acid  with  excess  of 
sodium  or  magnesium  sulphate  or  sodium  chlorid,  when  boiled 
with  the  solution  of  the  proteid,  mercuric  chlorid,  silver  nitrate, 
lead  acetate,  tannin,  and  alcohol.  Tannin  and  alcohol  will  pre- 
cipitate peptone,  but  most  of  the  others  will  not. 


ALBUMINS. 


107 


Classification  of  Proteids.  —  The  proteids  are  classified  as 
follows  : 

C  Serum-albumin. 

AH-  Egg-albumin. 

Albumms    •  .  •    .....      ,   llctalbumin. 

(^  Myo-albumin. 

f  Acid-albumin. 
j  Alkali-albumin. 

f  Serum-globulin  (paraglobulin). 
Fibrinogen. 


Albummates 


Nucleoproteids 


Proteoses 


PePtones 


Coagulated  Proteids  .    . 
Poisonous  Proteids. 


Lactoglobulin. 
Crystallin. 


f  Albumoses. 
Globuloses. 
<J   Vitelloses. 
|   Caseoses. 
(^  Myosinoses,  etc. 

f  Parapeptone. 

Prcmetone. 
|   Hemipeptone. 
[  Antipeptone,  etc. 

|  Fibrin. 
<   Myosin. 
(  Casein. 


ALBUMINS. 

These  are  sometimes  described  under  the  name  of  native 
albumins.  They  are  soluble  in  water,  dilute  saline  solutions,  and 
saturated  solutions  of  sodium  chlorid  and  magnesium  sulphate. 
When  their  solutions  are  saturated  with  ammonium  sulphate  the 
albumins  are  precipitated,  and  when  heated  to  a  temperature  of 
about  70°  C.  they  are  coagulated.  It  is  important  to  distinguish 
between  precipitation  and  coagulation.  As  just  stated,  the  albu- 
mins are  precipitated  by  ammonium  sulphate  ;  but  they  still  retain 
their  identity  and  solubility.  When,  however,  they  are  coagulated 
they  become  insoluble  and  are  changed  into  a  form  known  as 


108  PROTEIDS. 

coagulated  proteid.  Some  proteids  are  precipitated  by  certain 
reagents,  and  not  by  others,  and  this  fact  is  made  use  of  to  dis- 
tinguish the  proteids  from  one  another. 

The  following  table  gives  the  temperature  at  which  the  differ- 
ent albumins  coagulate : 

Albumins.  Temperature. 

Serum-albumin     a) 73°  C. 

«  B)    ,  77° 

7) 84° 

Egg-albumin 73° 

Lactalbumin 77° 

Myo-albumin ' 73° 

Serum-albumin. — The  fluid  of  blood  in  its  normal  condi- 
tion is  plasma;  after  coagulation,  serum.  The  albumin  of  blood 
remains  in  the  serum  after  blood  has  coagulated,  and  hence  is 
known  as  serum-albumin.  When  to  plasma  or  serum  is  added  an 
equal  amount  of  a  saturated  solution  of  ammonium  sulphate,  the 
fluid  is  said  to  be  half  saturated  with  ammonium  sulphate.  In 
this  condition  the  globulins  and  nucleoproteids  are  precipitated, 
but  not  the  albumin.  The  same  result  is  obtained  by  completely 
saturating  it  with  magnesium  sulphate.  If  now  the  fluid  is  filtered, 
the  globulins  and  nucleoproteids  will  be  filtered  out,  and  the  fil- 
trate (the  liquid  which  has  passed  through  the  filter)  may  be  put 
into  a  dialyzer,  and  the  salts  will  thus  be  removed,  leaving  only 
the  serum-albumin.  The  fact  that  exposure  of  serum-albumin  to 
different  temperatures  (about  73°  C.,  77°  C.,  and  84°  C.)  results 
in  three  separate  coagulations  indicates  that  what  is  called  serum- 
albumin  is  in  reality  three  different  substances  or  forms,  which  are 
called  respectively  a-albumin,  which  coagulates  at  72°  to  75°  C. ; 
^-albumin, coagulating  at  77°  to  78°  C. ;  and  /-albumin,  coagulating 
at  83  to  86°  C.  Halliburton,  to  whom  we  owe  this  information,  has 
ascertained  that  in  the  plasma  of  the  horse,  ox,  and  sheep  a-albumin 
is  absent,  while  /9-albumin  and  y-albumin  are  present ;  in  the  rep- 
tiles, amphibians,  and  fishes,  the  blood  of  which  he  examined,  only 
a-albumin  was  normally  found,  while  in  that  of  man  and  of  all 
other  mammals  and  birds  all  three  were  present. 

Magnesium  sulphate  does  not  precipitate  serum-albumin,  while 
it  does  serum-globulin,  so  that  by  this  reagent  the  two  may  be 
separated,  the  salt  being  added  in  crystals  until  the  solution  is 
completely  saturated ;  or,  as  stated,  half-saturation  with  ammo- 
nium sulphate  will  bring  about  the  same  result. 

The  specific  rotatory  power  of  solutions  of  serum-albumin  is 
-56°. 

Kgfg-albumin. — As  its  name  implies,  egg-albumin  is  obtained 
from  the  white  of  egg.  If  much  of  it  is  taken  in  the  food,  or  if 
it  is  injected  into  the  blood,  part  of  it  appears  in  the  urine. 
When  shaken  with  ether  it  is  precipitated.  Nitric  acid,  heat,  and 


ALKALI-ALBUMIN.  109 

the  prolonged  action  of  alcohol  coagulate  egg-albumin  ;  and  mer- 
curic chlorid,  nitrate  of  silver,  and  lead  acetate  precipitate  it, 
forming  insoluble  compounds. 

I/actalbutnin. — This  physiologic  ingredient  occurs  in  the 
milk  together  with  two  other  proteids,  caseinogen  and  lactoglobu- 
lin.  Half-saturation  with  ammonium  sulphate  precipitates  the 
caseinogen  and  lactoglobulin,  and  the  lactalbumin  which  remains 
in  solution  may  be  precipitated  by  saturation  with  sodium  sulphate. 
A  temperature  between  70°  and  80°  C.  (about  77°  C.)  will  coagu- 
late it.  Unlike  serum-albumin,  it  consists  of  but  a  single  proteid. 
Its  percentage  composition  is:  C,  52.19;  H,  7.18 ;  N,  15.77; 
S,  1.73;  O,  23.13. 

Myo-aibumin. — This  is  the  albumin  of  muscle,  and  resembles 
serum-albumin. 

ALBUMINATES. 

The  members  of  this  group  are  sometimes  described  under  the 
name  derived  albumins,  because  they  are  derived  from  albumin  by 
the  action  of  acids  or  alkalies.  Globulins,  when  treated  in  the 
same  manner,  also  produce  albuminates.  When  a  mineral  sub- 
stance is  added  to  a  solution  of  albumin,  a  new  compound  is 
formed,  which  is  denominated  an  albuminate  of  the  mineral,  but 
as  such  products  are  not  physiologic  ingredients  we  shall  not  con- 
sider them.  Albuminates  are  insoluble  in  water  and  neutral  solu- 
tions containing  no  salt ;  soluble  in  acids,  alkalies,  and  dilute  saline 
solutions ;  precipitated  when  saturated  with  sodium  chlorid  or 
magnesium  sulphate ;  and  are  not  coagulated  by  heat. 

Acid-albumin. — This  is  the  product  of  the  action  of  a  dilute 
acid — hydrochloric,  for  instance — upon  an  albumin.  In  this  con- 
version the  proteid  undergoes  important  changes.  Its  solution  is 
not  coagulated  by  heat,  and  when  it  is  neutralized  the  proteid  is 
precipitated.  The  conversion  from  the  native  to  the  acid-albumin 
is  gradual,  and  is  hastened  by  heat,  care  being  taken  that  the  tem- 
perature is  not  sufficiently  high  to  coagulate  it.  Globulins  are 
likewise  converted  into  acid-albumins  by  the  same  means,  but 
more  readily,  while  coagulated  proteids  or  fibrin  require  the  acid 
to  be  concentrated. 

By  some  writers  the  term  syntonin  is  applied  to  the  particular 
acid-albumin  resulting  from  the  globulin  myosinogen  ;  while  others 
use  it  as  a  synonym  for  acid-albumin  in  general. 

The  point  of  special  physiologic  interest  in  connection  with 
acid-albumin  is  that  in  the  process  of  stomach-digestion  it  is  one 
of  the  products. 

Alkali-albumin. — As  acids  acting  upon  albumins  and  globu- 
lins produce  acid-albumin,  in  a  similar  manner  alkalies  produce 
alkali-albumin.  There  is  an  interesting  historic  point  in  connec- 
tion with  this  proteid.  Mulder  found  that  by  heating  albumin 


110  PROTEIDS. 

with  caustic  potash  a  product  was  obtained  which  he  regarded 
as  the  basis  of  all  albuminous  substances,  and  to  which  he  gave 
the  name  of  "  protein."  Under  this  theory  proteids  are  supposed  to 
be  modifications  of  protein,  but  the  theory  is  an  obsolete  one,  and 
Mulder's  protein  is  nothing  more  than  alkali-albumin.  Alkali- 
albumin  is  produced  in  the  small  intestine  when  the  albumins  and 
globulins  of  the  food  are  acted  upon  by  the  alkali  of  the  pancreatic 
juice. 

GLOBULINS. 

The  members  of  this  group  are  soluble  in  dilute  saline  solu- 
tions, as,  for  instance,  1  per  cent,  sodium  chlorid,  insoluble  in 
water,  concentrated  solutions  of  sodium  chlorid,  magnesium  sul- 
phate, and  ammonium  sulphate,  and  are  coagulated  by  heat. 

The  following  table  gives  the  temperatures  at  which  the  im- 
portant globulins  coagulate : 

Globulins.  Temperature. 

Serum-globulin     75°  C. 

Fibrinogen 56° 

Myosinogen 56° 

Crystallin 73° 

Serum-globulin  (Paraglobulin). — Fibrinoplastin  is  another 
name  for  this  proteid,  given  to  it  at  a  time  when  it  was  believed 
that  it  was  connected  with  the  process  by  which  fibrin  was  formed, 
as  in  the  coagulation  of  blood.  It  exists  in  human  plasma  to  the 
extent  of  about  3  per  cent.  It  exists  also  in  lymph  and  chyle. 

Fibrinogen. — This  globulin  is  associated  with  serum-globulin 
in  plasma,  lymph,  and  chyle.  It  is  a  substance  of  great  interest, 
inasmuch  as  upon  its  presence  the  coagulability  of  blood  depends, 
a  process  in  which  the  soluble  fibrinogen  becomes  insoluble  fibrin. 
It  is  precipitated  by  half-saturating  with  sodium  chlorid,  and  by 
this  means  may  be  separated  from  serum-globulin. 

Fibrin. — Fibrin  is  obtained  by  whipping  blood  with  twigs  or 
wires.  The  material  that  clings  to  these  is  fibrin  together  with 
some  of  the  blood-corpuscles,  which  become  entangled  in  its 
meshes.  These  may  be  washed  out  in  running  water.  When  ex- 
amined with  the  microscope  fibrin  is  seen  to  be  made  up  of  threads 
which  intertwine  with  one  another,  forming  a  network.  Dry  fibrin 
is  obtainable  from  blood  to  the  amount  of  from  0.2  to  0.4  per 
cent,  of  its  weight.  Its  percentage-composition  is  C,  52.68 ;  H, 
6.83;  N,  16.91  ;  S,  1.10;  O,  22.48.  It  is  soluble  in  5  to  10  per 
cent,  solutions  of  sodium  chlorid,  sodium  sulphate,  magnesium 
sulphate,  and  some  other  salts.  It  swells  in  hydrochloric  acid 
of  0.2  per  cent,  strength  and  becomes  acid-albumin  and  proteoses. 
If  pepsin  is  also  present,  this  change  takes  place  more  quickly, 
the  fibrin  becoming  converted  into  two  globulins,  one  coagulating 
at  56°  C.  and  the  other  at  75°  C.,  and  then  becoming  acid-albu- 


TRUE  NUCLEINS.  Ill 

min,  proteoses,  and  finally  peptones.  Trypsin  acts  as  does  pepsin, 
except  that  the  reaction  must  be  alkaline,  not  acid,  the  products 
being  alkali-albumin,  proteoses,  and  peptones. 

In  speaking  of  the  ash  produced  when  fibrin  is  burnt,  Schafer 
says  that  it  invariably  contains  lime,  but  not  more  than  other  pro- 
teids,  nor  more  than  the  fibrinogen  from  which  it  is  formed.  This 
fact  completely  disposes  of  the  theories  of  coagulation  which  as- 
sume that  fibrin  is  merely  a  combination  of  fibrinogen  with  lime, 
such  as  those  of  Freund,  Arthus,  Pekelharing,  and  Lilienfeld. 

Myosinogen. — This  globulin  occurs  in  muscular  tissue,  and 
in  the  condition  called  rigor  mortis  coagulates,  and  in  this  condi- 
tion is  myosin  or  muscle-clot.  A  similar  change,  heat-rigor,  occurs 
when  muscle  is  heated,  coagulation  taking  place  when  the  temper- 
ature reaches  47°  to  50°  C. ;  and  a  second  coagulation  at  56°  C. 
This  is  due  to  the  fact  that  there  are  two  globulins :  paramyo- 
sinogen  which  coagulates  at  the  lower,  and  myosinogen  at  the 
higher  temperature. 

I/actoglobulin. — This  proteid  is  found  in  cows'  milk  in  such 
minute  quantity  that  it  has  escaped  the  analyses  of  excellent 
chemists. 

Crystallin. — The  proteid  matter  of  the  crystalline  lens  is 
crystallin,  and  exists  in  that  structure  to  the  amount  of  34.93  per 
cent.  Two  varieties  of  crystallin  are  described  :  a-crystallin  and 
/9-crystallin,  differing  in  composition,  specific  rotatory  power,  and 
coagulation-point.  The  former  is  more  abundant  in  the  outer 
portion  of  the  lens ;  the  latter,  in  the  inner. 


NUCLEOPROTEIDS. 

These  substances  are  composed  of  nucleins  and  proteids,  and 
occur  in  the  nuclei  and  protoplasm  of  cells.  Nucleins  have  been 
obtained  from  the  nuclei  of  pus-corpuscles,  spermatozoa,  yolk  of 
egg,  yeast,  liver,  brain,  and  cows'  milk.  The  term  nucleins  is  used 
rather  than  nuclein  because  there  are  several  of  these  substances, 
differing  in  solubility  and  chemical  composition.  They  are  divided 
by  Hoppe-Seyler  into  three  groups : 

1.  Nucleins  which  consist  only  of  nucleic  acid,  whose  formula 
is  not  definitely  known,  but  is  approximately  C40H54N4O17(P2O5)2. 
Indeed,  nucleic  acid  is  itself  probably  not  a  single  substance,  no 
less   than    four  having  been  found  by  investigators.     This  acid 
does  not  give  the  reactions  of  proteid,  but  is  characterized  by  its 

freat  affinity  for  basic  dyes,  such  as  methyl-green  (see  Karyo- 
inesis,   p.  28).      Nucleins  of  this  group  occur  in  spermatozoa. 

2.  True  Nucleins. — These  occur  in  the  nuclei  of  cells,  and 
on    decomposition    yield    proteid,    xanthin    bases    (hypoxanthin, 
xanthin,  guanin,  adenin),  and  phosphoric  acid.    The  true  nucleins, 
which   contain  the  most  nucleic   acid,  are  obtainable  from   the 


112  PROTEIDS. 

chromatin  fibers  of  the  nucleus ;  those  which  occur  in  the  nucleoli 
contain  less  nucleic  acid. 

3.  Pseud onucleins. — These  are  sometimes  called  paranucle- 
ins,  and  are  obtainable  from  the  nucleoproteids,  such  -as  caseinogen 
and  vitellin.  They  yield  none  of  the  bases  as  do  the  true  nucleins, 
but  only  proteid  and  phosphoric  acid. 

The  nucleoproteids  are  divided  into  two  groups :  1.  Those 
which  yield  true  nucleins  on  gastric  digestion,  and  to  which  Ham- 
marsten  restricts  the  name  " nucleoproteids;"  and  2.  Those  which 
yield  pseudonucleins  on  gastric  digestion,  called  by  Hammarsten 
"  nucleo-albtimins."  In  this  latter  group  are  caseinogen  and  vitellin. 
To  make  this  resume  complete,  mention  should  be  made  of  the 
phospho-glucoproteids.  A  glucoproteid  is  a  compound  of  proteid 
with  a  carbohydrate,  and  includes  mucins  among  other  substances. 
From  mucins  a  carbohydrate  may  be  obtained  called  animal  gum, 
which  when  acted  upon  by  a  dilute  mineral  acid  is  converted  into 
a  reducible  but  non-fermentable  sugar  having  the  formula  C6H12O6. 
Most  of  the  glucoproteids  contain  no  phosphorus,  but  some  do, 
and  these  constitute  the  phospho-glucoproteids.  There  is  some 
evidence  to  show  that  from  many  of  the  proteid s  (acid-  and  alkali- 
albumin,  serum-albumin,  serum-globulin)  a  reducing  substance  may 
be  obtained,  which  may  be  a  carbohydrate. 

Caseinogen. — This  was  formerly  regarded  as  an  alkali- 
albumin,  but  is  now  placed  among  the  nucleoproteids ;  and  if  we 
accept  the  classification  of  Hammarsten,  it  would  be  placed  among 
the  nucleo-albumins,  for  the  reason  that  on  gastric  digestion  it 
yields  pseudonuclein. 

Caseinogen  is  the  most  abundant  proteid  of  milk,  the  two  other 
proteids  being  lactoglobulin  and  lactalbumin,  and  may  be  obtained 
from  it  by  saturation  with  sodium  chloric!  or  magnesium  sulphate, 
or  by  half-saturation  writh  ammonium  sulphate.  It  is  not  coagu- 
lated by  heat.  Human  caseinogen  has  the  following  percentage- 
composition  :  C,  52.24;  H,  7.31;  N,  14.9;  P,  0.68;  S,  1.17; 
O,  23.66 ;  and  yields  no  pseudonuclein  on  gastric  digestion. 
When  acted  upon  by  rennet  caseinogen  coagulates,  becoming 
casein,  which  is  solul)le  in  dilute  alkalies,  such  as  lime-water. 
Rennet  is  obtained  from  the  stomach  of  the  calf,  and  owes  its 
property  of  coagulating  caseinogen  to  the  enzyme  rennin,  also 
called  chymosin.  Upon  the  addition  of  rennet  to  cows'  milk  a 
curd  or  clot  is  formed,  which  consists  of  casein  and  the  fat  of  the 
milk  ;  the  liquid  portion  of  the  milk,  after  the  curd  is  formed,  is 
whey,  consisting  of  water  holding  in  solution  the  proteids,  lacto- 
globulin and  lactalbumin,  lactose,  and  the  salts.  Another  proteid, 
whey-proteid,  is  produced  from  the  decomposition  of  that  portion 
of  the  caseinogen  which  is  not  changed  into  casein.  The  curd  of 
human  milk  is  of  a  softer  and  more  flocculent  character  than  that 
of  cows'  milk,  and  to  render  the  curd  of  the  latter  more  like  that 


POISONOUS  PEOTEIDS.  113 

of  the  former,  and  thus  aid  digestion  in  the  infant,  lime-water 
or  barley-water  is  sometimes  added,  simple  dilution  with  water 
or  boiling  the  milk  producing  the  same  effect. 

One  essential  condition  for  coagulation  of  caseinogen  is  the 
presence  of  calcium  salts ;  and  if  these  salts  are  precipitated,  as 
they  may  be  by  the  addition  of  potassium  oxalate,  coagulation 
does  not  take  place.  The  details  of  the  coagulating  process  are  as 
follows  :  The  enzyme,  rennin,  converts  the  caseinogen  into  soluble 
casein,  which  is  then  precipitated  by  the  calcium  salts,  the  curd 
being  probably  caseate  of  lime. 

Vitellin. — This  is  the  principal  constituent  of  the  yolk  of  egg. 
It  is  described  by  some  writers  as  containing  phosphorus ;  others 
regard  the  phosphorus  as  being  an  impurity — that  is,  as  a  constit- 
uent of  the  nuclein  or  lecithin  which  is  associated  with  the  vitellin. 
The  most  recent  analyses  seem  to  demonstrate  that  phosphorus 
does  not  exist  in  vitellin.  It  is  altogether  probable  that  several 
substances  are  included  under  the  name  "  vitellin." 

PROTEOSES  AND  PEPTONES. 

The  members  of  these  two  groups  will  be  discussed  in  connec- 
tion with  the  gastric  and  intestinal  digestion  of  proteids. 

COAGULATED  PROTEIDS. 

Under  this  title  are  included  Fibrin,  Myosin,  and  Casein,  which 
are  discussed  in  connection  with  Fibrinogen,  Myosinogen,  and 
Caseinogen,  together  with  such  others  as  are  produced  by  the 
action  of  heat  on  proteids. 

POISONOUS  PROTEIDS. 

That  poisonous  proteids  of  both  vegetable  and  animal  origin 
exist  has  been  abundantly  demonstrated.  Among  those  of  vege- 
table origin  are  the  following :  Abrin,  a  compound  of  a  globulin 
and  a  proteose,  obtained  from  the  seeds  of  jequirity,  Abrus  preca- 
torius  ;  papain,  or  a  proteid  associated  with  it,  obtained  from  the 
fruit  of  the  papaw-tree,  Carica  papaya;  ricin,  from  the  seeds 
of  castor-oil,  Ricinus  communis  ;  and  lupino-toxin,  from  iMpinus 
luteum. 

The  number  of  poisonous  proteids  of  animal  origin  is  not 
inconsiderable,  of  which  may  be  mentioned:  Snake-poison;  pro- 
teids from  the  serum  of  some  eels,  those  from  some  spiders,  and 
the  stinging  apparatus  of  some  insects;  ordinary  peptones  and 
proteases,  as  is  shown  by  the  fact  that  0.3  gram  of  commercial 
peptone  per  kilogram  of  body-weight  will  kill  a  dog  when  injected 
into  its  blood  ;  some  nucleoproteids,  as  Wooldridge's  tissue  fibrino- 
gens,  which  cause  the  blood  to  coagulate  in  the  vessels  when 


114 


PROTEIDS. 


injected  into  them  ;  and  various  proteids  produced  by  bacteria,  the 
so-called  toxalbumoses. 

The  two  classes  of  these  poisonous  proteids  which  demand  more 
than  a  passing  notice  are  snake-poison  and  the  bacterial  poisons. 

Snake-poison. — The  first  snake-poison  isolated  was  viperin 
from  an  adder.  Subsequently  crotalin  was  obtained  from  the 
venom  of  a  rattlesnake,  and  its  albuminous  nature  was  recognized  ; 
and  later  the  venom  of  the  cobra  and  other  poisonous  snakes  was 
studied.  It  has  been  demonstrated  that  in  the  venom  of  the  Aus- 
tralian black  snake  there  are  three  proteids  :  One,  a  non-virulent 
albumin,  and  the  two  others,  which  are  virulent,  are  proto-  and 
heteroproteose.  The  poison  produces  intravascular  coagulation  of 
the  blood,  probably  by  causing  a  disintegration  of  the  cells  of  the 
endothelium  of  the  vessels  or  of  the  red  corpuscles,  thereby  pro- 
ducing or  setting  free  a  nucleoproteid.  In  discussing  this  sub- 
ject, Halliburton,  in  Schafer's  Physiology,  to  which  we  are  indebted 
for  this  resume  of  proteids  or  poisons,  says  that  with  regard  to  the 
question  how  these  poisonous  proteoses  are  formed,  C.  J.  Martin 
puts  forward  the  following  hypothesis  :  The  cells  of  the  venom- 
gland  exercise  a  hydrolyzing  (p.  119)  agency  on  the  albumin  sup- 
plied them  by  the  blood,  the  results  of  which  influence  are  the 
poisonous  proteoses  found  in  the  venom.  A  difference  between 
the  process  and  digestion  by  pepsin,  or  by  anthrax  bacilli,  is  that 
the  hyd  ration  stops  short  at  the  proteose  stage,  and  is  not  con- 
tinued so  as  to  form  peptone,  or  simple  nitrogenous  materials,  like 
leucin,  ty rosin,  or  alkaloids.  Gland  epithelium  is  certainly  capable 
of  exercising  such  a  hydrolyzing  influence ;  the  conversion  of 
glycogen  into  sugar  in  the  liver-cells  is  one  of  the  best  known 
examples.  The  following  table  is  given  illustrating  the  analogy 
between  various  hydrolyzing  processes,  proteid  being  in  all  cases 
the  material  acted  on  : 


Primary  Agents. 

Ferment. 

Products. 

Albuminous. 

Nitrogenous  but  not  Albuminous. 

1.  Epithelial  cell  of 
gastric  gland. 
2.  Epithelial  cell  of 
pancreas. 
3.  Bacillus     anthra- 
cis. 
4.  Bacillus  diphthe- 
rise. 
5.  Epithelial  cell  of 
snake's  venom- 
gland. 

Pepsin. 
Trypsin. 

None   yet 
found. 
Ferment  not 
named. 
None    yet 
found. 

Proteoses,  peptone. 
Proteoses,  peptone. 
Proteoses,  peptone. 
Proteoses. 
Proteoses. 

Brieger's  peptotoxin,  a  very 
doubtful  basic  substance. 
Leucin,   tyrosin,  lysin,  arginin, 
aspartic  acid,  ammonia. 
Leucin,  tyrosin,  and  an  anthrax 
alkaloid. 
Organic  acid  of  doubtful  nature. 

Trace  of  organic  acid. 

It  has  been  ascertained  that  0.00025  gram  of  the  venom  of 
Hoplocephalus  custus,  an  Australian  snake,  will  kill  a  rabbit  weigh- 
ing a  kilogram  ;  this  is  about  the  same  virulence  as  the  toxin  of 
diphtheria. 

Bacterial  Poisons.— Halliburton  says  that  the  word  pto- 
main  was  originally  employed  to  designate  those  putrefaction-prod- 


GELATIN.  115 

ucts  of  animal  substances  which  give  the  reactions  of  vegetable 
alkaloids,  and  which  are  more  or  less  poisonous.  The  similar  sub- 
stances formed  by  metabolic  activity,  either  from  lecithin  or  pro- 
teids,  are  called  leukomains.  One  of  these  alkaloids,  tyrotoxicon, 
has  been  obtained  from  putrid  cheese  ;  another,  mytilotoxin,  from 
muscles,  and  there  are  others.  Brieger  obtained  poisonous  alka- 
loids, which  he  called  toxins,  from  cases  of  typhoid  fever  and 
tetanus,  calling  that  from  the  former  iyphotoxin  and  the  latter 
tetanin. 

From  this  brief  consideration  of  the  subject  it  will  be  seen  that 
both  ptomains  and  toxalbumoses  may  be  produced  by  bacteria. 

ALBUMINOIDS. 

The  term  albuminoids  implies  that  the  members  of  this  class 
resemble  albumin  ;  indeed,  they  bear  a  resemblance  to  all  the  pro- 
teids,  but  also  differ  from  them  in  important  particulars.  The 
members  of  the  class  are :  Collagen,  Gelatin,  Elastin,  Reticulin, 
Keratin,  Neurokeratin,  Mucin,  and  Nuclein. 

Collagen. — This  is  the  substance  in  the  white  fibers  of  con- 
nective tissue  which  produces  gelatin.  In  bones  it  exists  under 
the  name  of  ossein,  associated  with  some  other  organic  substances. 
There  exists  in  hyaline  cartilage  a  substance  which  has  long  borne 
the  name  of  chondrigen,  \vhich  when  boiled  was  said  to  produce 
chondrin,  but  it  is  now  known  that  "  chondrigen  "  is  a  mixture  of 
collagen  and  mucin  or  mucinoid  substances. 

Collagen  is  insoluble  in  water,  dilute  acids,  and  alkalies.  When 
treated  with  boiling  water  or  with  pepsin  and  hydrochloric  acid 
it  becomes  gelatin.  It  is  considered  to  be  the  anhydrid  of  gela- 
tin, as  is  expressed  by  the  following  equation  : 

Cio2H15lN3lO29  —  H2O  =  C^HugN^Ojjg 

Gelatin.  Water.  Collagen. 

It  should  be  said,  however,  that  these  formulae  have  not  been 
definitely  established.  Indeed,  another  formula  has  been  given 
for  gelatin  by  an  equally  competent  chemist :  C76H124N34O29.  In 
neither  of  these  formulae  does  sulphur  occur ;  when  it  has  been 
found  on  analysis  it  has  been  regarded  by  some  as  an  impurity, 
while  one  authority,  at  least,  believes  it  to  be  an  integral  part  of 
both  collagen  and  gelatin  to  the  amount  of  0.6  per  cent. 

Gelatin. — Gelatin  is  insoluble  in  cold  but  soluble  in  hot  water  ; 
and  when  the  solution  cools  it  gelatinizes  or  forms  a  jelly.  It 
reacts  with  Millon's  reagent,  and  with  copper  sulphate  and  caustic 
potash  it  gives  a  violet  color.  Tannic  acid  precipitates  it,  and 
upon  this  depends  the  process  of  tanning.  It  is  levorotatory,  the 
amount  of  rotation  being  about  —130°.  If  gelatin  is  boiled  for 
twenty-four  hours,  its  power  to  gelatinize  is  lost,  and  it  becomes 


116  ALB  UMINOIDS. 

gelatin-peptone.  When  acted  on  by  pepsin  and  hydrochloric 
acid,  as  during  gastric  digestion,  it  becomes  protogelatose,  then 
deuterogelatose,  and  lastly  gelatin-peptone.  A  similar  set  of 
changes  results  from  the  action  of  the  trypsin  of  the  pancreatic 
juice. 

Gelatin  is  a  "  proteid-sparing  "  substance — that  is  to  say,  that 
while  it  cannot  take  the  place  of  the  proteids  as  a  tissue-former,  its 
nitrogen  not  being  available  for  that  purpose,  yet  it  does  serve  a 
useful  purpose  as  food.  When  gelatin  is  used  as  food  to  replace  en- 
tirely the  proteids,  the  animals  experimented  upon  starve  to  death. 
The  gelatoses  and  gelatin-peptones  which  result  from  its  digestion 
are  oxidized,  as  are  carbohydrates  and  fats,  producing  CO2,  H2O, 
and  probably  urea.  It  is  a  source  of  energy,  therefore,  and  in  so 
far  as  it  fulfils  this  office  it  takes  the  place  of  proteids,  even 
though,  unlike  them,  it  cannot  supply  the  waste  of  nitrogenous 
tissues.  It  "spares"  the  proteids  more  than  do  carbohydrates, 
and  still  more  than  fats.  Thus  proteids  serve  in  the  economy 
a  double  purpose :  (1)  as  tissue-formers  and  (2)  as  sources  of 
energy.  It  is  in  this  latter  regard  that  gelatin  can  replace  the 
proteids.  It  has  been  found,  however,  that  when  gelatin  is  given 
to  replace  proteids  the  amount  given  must  be  twice  that  which  it 
is  designed  to  replace ;  practically  it  has  been  shown  that  one-fifth 
the  amount  of  proteid  may  be  thus  replaced. 

Elastin. — From  the  yellow  fibers  of  connective  tissue  is 
obtained  this  member  of  the  albuminoid  class.  It  has  the  fol- 
lowing approximate  percentage-composition  :  C,  54.24  ;  H,  7.27  ; 
N,  16.7  ;  O,  21.69  ;  S,  0.3.  Some  authorities  regard  the  sulphur 
as  an  impurity.  Elastin,  like  collagen,  but  less  easily,  is  changed 
by  hydrochloric  acid  and  pepsin,  and  also  by  trypsin/ the  products 
being  proto-elastose  and  deutero-elastose ;  but  unlike  collagen  the 
change  goes  no  further — that  is,  no  peptone  is  formed  in  either 
case. 

Reticulin. — Retiform  or  reticular  tissue,  such  as  occurs  in 
lymphatic  glands,  is  in  many  respects  so  similar  to  ordinary  are- 
olar  tissue  that  so  eminent  an  authority  as  Schafer  regards  the 
former  simply  as  a  variety  of  connective  tissue ;  but  others  claim 
that  while  there  are  no  histologic  points  of  difference,  yet  from  a 
chemical  standpoint  there  is  a  marked  difference,  and  this  consists 
in  the  presence  in  the  fibers  of  reticuHn,  whose  percentage-compo- 
sition is  C,  52.88  ;  H,6.97;  N,15.63;  S,  1.88  ;  P,  0.34;  ash,  2.27. 
The  absence  of  glutaminic  acid  among  the  decomposition-products 
of  reticulin,  while  it  is  present  in  those  of  collagen  and  gelatin, 
is  one  of  the  points  relied  upon  to  establish  the  difference  between 
the  two  tissues. 

In  discussing  this  subject  Halliburton  says:  "We  are,  there- 
fore, confronted  with  the  difficulty  that  the  fibers  of  reticular 
tissue  are  anatomically  continuous  with  and  histologically  identical 


ENZYMES.  117 

with  the  white  fibers  of  connective  tissue,  and  yet  they  contain 
chemically  this  new  material.  The  answer  to  the  problem  is 
probably  that  reticulin  is  not  specially  characteristic  of  reticular 
fibers,  but  is  present  in  all  white  connective-tissue  fibers." 

Keratin. — This  substance  is  found  in  all  horny  tissues,  such 
as  hair,  nails,  and  epidermis.  It  is  soluble  in  water  at  150°- 
200°  C.,  and  in  alkalies,  but  is  unaffected  by  pepsin  or  trypsin, 
and  contains  a  large  amount  of  sulphur.  Its  percentage-composition 
in  hair  is  as  follows:  C,  50.60;  H,  6.36;  N,  17.14;  O,  20.85; 
S,  5.  In  the  skin  the  change  of  the  protoplasm  of  the  cells 
into  keratin  takes  place  in  two  strata  which  are  between  the 
Malpighian  layer  and  the  horny  layer — the  stratum  lucidum,  next 
to  the  horny  layer,  and  the  stratum  granulosum,  next  to  the 
Malpighian.  In  the  latter  the  cells  contain  eleidinj  which  is 
regarded  as  an  intermediate  stage  in  the  conversion  of  the  pro- 
toplasm into  keratin. 

Neurokeratin. — A  modified  form  of  keratin,  neurokeratin, 
occurs  in  the  medullary  sheath  of  nerves  and  in  neuroglia.  Its 
percentage  composition  varies  considerably,  being  in  some  portions 
of  the  nervous  system  as  low  as  0.3,  and  in  others  as  high  as  2.9. 

Mucins. — Inasmuch  as  mucin  is  not  a  single  substance,  but 
consists  rather  of  several  varieties,  differing  in  solubility  in  acid 
and  alkaline  solutions,  it  is  more  correct  to  speak  in  the  plural. 
Mucin  is  an  ingredient  of  mucus,  the  product  of  mucous  glands, 
and  it  exists  also  in  the  ground-substance  of  connective  tissue. 
Mucins  give  the  characteristic  viscidity  to  the  fluids  in  which 
they  occur ;  they  are  soluble  in  alkalies,  and,  when  so  dissolved, 
can  be  precipitated  by  acetic  acid.  When  they  are  treated  with 
superheated  steam  a  carbohydrate  called  animal  gum  is  split  off, 
the  formula  of  which  is  C6H10O5.  When  this  latter  is  treated 
with  a  dilute  mineral  acid  it  is  changed  into  a  reducing  but  not 
fermentable  sugar,  whose  formula  is  C6H12O6.  It  is  an  interesting 
fact  that  from  other  albuminoids,  and  also  from  proteids,  carbo- 
hydrates may  be  obtained.  The  percentage-composition  of  sub- 
maxillary  mucin  is:  C,  48.84 ;  H,  6.80 ;  N,  12.32;  O,  31.20; 
S,  0.84. 

Nuclein. — This  substance  has  been  sufficiently  discussed  in 
connection  with  the  nucleoproteids  (p.  111). 

ENZYMES. 

There  are  two  varieties  of  ferments :  (1)  organized  ferments, 
of  which  yeast  is  an  example,  and  (2)  unorganized  or  soluble  fer- 
ments, of  which  pepsin  is  an  example.  It  has  been  proposed  to 
limit  the  term  ferment  to  the  organized  class,  and  to  denominate, 
the  changes  which  its  members  cause  in  substances  upon  which 
they  act  as  fermentation,  and  to  the  soluble  or  unorganized  class 


118  ENZYMES. 

to  apply  the  name  of  enzyme,  and  to  apply  to  the  process  for  which 
its  members  are  responsible  the  term  zymolysis. 

The  distinction  between  the  organized  and  unorganized  fer- 
ments is,  after  all,  probably  a  superficial  and  not  a  fundamental 
one.  The  fermentative  or  zymolytic  action  is  in  both  cases  due 
to  a  substance  which  cells  produce.  In  the  one  case,  that  of  an 
organized  ferment,  such  as  yeast,  this  product  is  thrown  out  by  the 
cells  of  the  yeast-plant  while  they  are  in  contact  with  the  substance 
acted  upon — dextrose,  for  example.  In  the  case  of  an  unorgan- 
ized ferment  or  enzyme — trypsin,  for  instance — the  cells  of  the 
pancreas  which  produce  it  remain  in  the  organ,  while  the  product 
is  poured  out  with  the  other  constituents  of  the  secretion  and 
brings  about  its  action  on  the  proteids  at  a  distance  from  the  cells. 
In  both  instances  it  is  the  product  of  cells  which  produces  the 
change.  There  will  here  be  discussed  only  the  unorganized  fer- 
ments or  enzymes. 

Some  of  the  enzymes  on  analysis  have  been  found  to  be  very 
similar  in  their  composition  to  the  proteids,  but  the  consensus  of 
opinion  is  that  they  are  not  proteids,  notwithstanding  this  resem- 
blance. The  failure  to  determine  their  exact  composition  is  due 
to  the  fact  that  as  yet  no  enzyme  has  been  obtained  pure  and  free 
from  proteids;  and  also  because  the  quantity  is,  in  any  event, 
exceedingly  small.  Like  most  proteids  they  are  not  diffusible, 
and  cannot  therefore  be  separated  from  them  by  dialysis. 

Enzymes  are  soluble  in  water,  and  are  precipitated  by  an  excess 
of  absolute  alcohol  or  by  saturation  with  ammonium  sulphate. 
They  are  changed  by  alcohol  only  when  the  contact  has  existed 
for  a  considerable  time ;  this  period  is,  however,  shorter  in  the 
case  of  pepsin  than  in  that  of  the  other  enzymes. 

Minute  quantities  of  enzymes  under  proper  conditions  'will 
bring  about  zymolytic  changes  in  considerable  quantities  of  the 
substances  upon  which  they  act,  apparently  without  suffering  any 
diminution.  Thus,  1  part  of  rennin  will  coagulate  800,000  parts 
of  milk,  and  pepsin  will  dissolve  in  seven  hours  500,000  times  its 
weight  of  fibrin.  The  conditions  under  which  they  act  vary  for 
each  enzyme ;  but,  as  a  rule,  high  temperatures  destroy  and  low 
temperatures  inhibit,  while  for  each  there  is  a  temperature  at  which 
its  action  is  the  most  pronounced  ;  this  is  called  the  "optimum  v 
temperature.  Thus  for  pepsin  the  optimum  temperature  is  from 
35°  to  40°  C.,  while  below  1°  C.  its  action  ceases,  as  it  does  also 
at  70°  C.,  while  boiling  permanently  destroys  it.  It  has  been 
determined,  however,  that  when  perfectly  dry  the  enzymes  may  be 
heated  to  160°  C.  without  destroying  their  power. 

An  interesting  fact  also  connected  with  the  enzymes  is,  that 
when  they  have  produced  a  considerable  amount  of  their  product 
their  action  is  diminished,  and  that  if  this  new  product  accumu- 
lates still  more,  the  zymolytic  action  of  the  enzymes  may  be 


HYDROLYSIS.  119 

brought  to  an  end,  although  their  power  to  act  would  still  be  pres- 
ent if  these  products  were  removed.  In  some  instances  the  enzyme 
is  not  the  direct  product  of  the  cells,  but  the  cells  form  what  is 
termed  a  zymogen,  which  is  afterward  converted  into  the  enzyme. 
Each  zymogen  is  named  from  the  enzyme  which  it  produces  :  thus 
the  zymogen  of  trypsin  is  trypsinogen.,  that  of  pepsin  is  pepsinogen, 
etc.  It  is  an  interesting  and  valuable  fact  that  chloroform  inhibits 
the  action  of  the  organized  ferments,  but  does  not  interfere  with 
that  of  the  enzymes. 

As  it  is  very  important  to  have  a  clear  idea  of  the  meaning 
of  certain  terms  which  occur  repeatedly  in  the  discussion  of  the  en- 
zymes and  their  action,  these  terms  will  here  be  defined,  namely  : 

Amylolytic  Enzyme. — The  conversion  of  amyloses  into 
sugar  is  an  amylolytic  change,  and  an  enzyme  which  has  the 
power  of  producing  this  change  is  an  amylolytic  enzyme ;  such 
are  ptyalin  of  the  saliva  and  amylopsin  of  the  pancreatic  juice. 

Diastatic  or  Diastasic  Enzyme. — There  exists  in  barley 
an  enzyme,  diastase,  which  has*  the  power  of  changing  starch  into 
sugar ;  the  change  itself,  and  also  the  enzyme,  are  spoken  of  as 
diastatic  or  diastasic.  It  will  be  seen,  therefore,  that  amylolytic, 
diastatic,  and  diastasic  are  synonymous. 

Proteolytic  Enzyme. — The  conversion  of  proteids  into  pro- 
teoses  and  peptones  is  a  proteolytic  change,  and  an  enzyme  which 
causes  it  is  a  proteolytic  enzyme ;  such  are  pepsin  of  the  gastric 
juice,  and  trypsin  of  the  pancreatic  juice. 

Steatolytic  Enzyme. — The  splitting  of  fats  into  fatty  acids 
and  glycerin  is  a  steatolytic  proces,  and  an  enzyme  which  has  this 
power  is  a  steatolytic  enzyme ;  such  is  steapsin  or  lipase  of  the  pan- 
creatic juice.  These  enzymes  are  also  termed  lipolytic  and  adipolytic. 

Sugar-splitting"  Enzymes. — These  enzymes  split  up  sugar ; 
thus,  invertin  or  invertase  splits  cane-sugar  into  glucose  and  levu- 
lose  or  fructose,  this  product  being  known  as  invert-sugar  (p.  92) ; 
lactase  splits  up  lactose  or  milk-sugar  into  glucose  and  galactose ; 
glucase  hydrolyses  maltose  into  glucose. 

Coagulating  Enzymes. — These  enzymes  change  soluble 
into  insoluble  proteids ;  such  are  rennin,  fibrin -ferment,  and  myo- 
sin-ferment. 

Activating  Enzymes. — In  the  intestinal  juice,  produced  by 
the  intestinal  epithelium,  there  is  an  enzyme  which  "  activates " 
trypsinogen — i.'e.,  changes  the  trypsinogen  into  the  active  trypsin  ; 
this  enzyme  is  called  enterokinase.  In  general,  enzymes  which 
have  the  power  of  activating  zymogens  are  called  kinases. 

Hydrolysis. — It  is  now  generally  accepted  that  in  many  of 
these  various  conversions  the  change  consists  in  the  assumption  of 
a  molecule  of  water ;  thus, 

(CoH.AX  +  H20  =  C6H1206 

Starch.  Water.  Sugar. 


120  METABOLISM. 

This  change  is  called  hydrolysis,  and  the  action  is  said  to  be 
hydrolytic.  Chemistry  has  established  this  fact  for  araylolytic  and 
inversive  enzymes,  and  it  is  probably  equally  true  for  those  that 
are  proteolytic.  For  the  action  of  all  enzymes  the  presence  of 
water  is  essential. 

The  consideration  of  the  individual  enzymes  will  be  deferred 
until  the  action  of  the  various  fluids  in  which  they  occur  is  dis- 
cussed. 

METABOLISM. 

The  human  body  is  during  life  the  seat  of  constant  activity, 
during  which  almost  limitless  chemical  changes  take  place.  These 
are  collectively  spoken  of  under  the  term  metabolism.  Some 
of  these  are  concerned  with  the  upbuilding  of  the  body,  and 
are  termed  anabolic;  while  others  result  in  the  wasting  of 
the  tissues,  and  are  denominated  katabolic.  Anabolism  and 
assimilation  may  be  regarded  as  synonymous  terms,  while  katab- 
olism  and  destructive  assimilation  express  somewhat  the  same 
idea.  The  word  metabolism  has  been  defined  as  "the  process 
by  which  living  cells  or  organisms  are  capable  of  incorporating 
substances  obtained  from  food  into  an  integral  part  of  their  own 
bodies ;  the  changes  that  proteids  and  other  constituent  substances 
undergo  in  the  body.  It  is  constructive  when  the  substance  be- 
comes more  complex ;  destructive  or  retrograde  when  it  becomes 
simpler  by  the  change."  Still  another  lexicographer  defines  metab- 
olism as  "  The  act  or  process  by  which,  on  the  one  hand,  the  dead 
food  is  built  up  into  living  matter,  and  by  which,  on  the  other, 
the  living  matter  is  broken  down  into  simple  products  within  a  cell 
or  organism  ;  the  sum  of  the  anabolic  or  constructive  (assimilation) 
and  the  katabolic  or  destructive  (decomposition)  processes."  If 
the  anabolic  and  katabolic  processes  should  exactly  balance  one 
another,  the  body  would  be  in  a  state  of  equilibrium,  but  this  never 
occurs  absolutely. 

As  a  result  of  the  destructive  changes  which  take  place  in 
the  body  it  is  essential  that  they  be  counterbalanced  so  far  as  is 
possible,  and  this  is  accomplished  by  taking  into  the  body  food 
and  oxygen.  If  an  individual  is  deprived  of  oxygen,  death  occurs 
in  a  few  minutes  from  asphyxia.  No  less  certainly  does  death 
supervene  if  he  is  deprived  of  food,  although  the  time  required  to 
bring  about  the  result  is  much  greater,  depending  considerably 
upon  the  circumstances  and  upon  the  age  of  the  individual.  In 
the  instance  frequently  quoted,  when,  in  the  year  1816,  one  hun- 
dred and  fifty  persons  were  wrecked  on  the  "  Medusa,"  all  but 
fifteen  were  dead  after  having  been  without  food,  either  solid  or 
liquid,  for  thirteen  days.  In  this  instance,  however,  it  must  be 
borne  in  mind  that  the  exposure  incident  to  the  shipwreck  proba- 
bly contributed  to  hasten  the  fatal  result.  It  may  be  said,  in 
general,  that  death  will  supervene  when  the  body  has  lost  four- 


INORGANIC  FOOD  STUFFS. 


121 


tenths  of  its  weight.  When  death  thus  occurs  from  starvation  the 
various  tissues  lose  different  amounts  proportionately.  The  fol- 
lowing table  gives  the  loss  in  percentage : 


Bone 5.4  ] 

Muscle 42.2 

Liver 4.8 

Kidneys 0.6 

Spleen 0.6 

Pancreas 0.1 

Lungs 0.3 

Heart  0.0 


Testes 0.1 

Intestine 2.0 

Brain  and  cord 0.1 

Skin  and  hair 8.8 

Fat 26.2 

Blood 3.7 

Other  parts 5.0 


From  this  table  it  will  be  seen  that  the  greatest  loss  takes  place 
in  the  muscles  and  fat. 

FOOD. 

Food  may  be  defined  as  material  taken  into  the  body  to  build  up 
its  tissues  and  repair  their  waste,  or  to  produce  energy.  In  the 
discussion  of  the  effects  of  alcohol  other  definitions  are  given 
(p.  158).  Foods  are  made  up  of  food-stuffs  and  other  substances 
associated  with  them,  which  latter,  being  indigestible,  are  of  no 
value  either  for  purposes  of  nutrition  or  for  the  generation  of 
energy. 

Food-stuffs  are  divided  into  four  classes,  which  have  already 
been  somewhat  discussed  in  treating  of  the  physiologic  ingredients. 
The  classes  of  food-stuffs  are :  Inorganic,  including  water  and 
salts  ;  Carbohydrates ;  Fats  or  oils ;  Proteids. 

Inorganic  Food-Stuffs. — Water  is,  as  has  been  pointed  out, 
one  of  the  most  important  ingredients  of  the  body,  and  is  there- 
fore one  of  the  most  essential  of  the  food-stuffs.  It  is  the  solvent 
of  many  of  the  constituents  of  the  food  and  the  salts,  and  by  its 
softening  action  aids  in  the  processes  by  which  the  hard  portions 
of  food  are  masticated  and  swallowed.  It  should  be  taken  in 
quantities  much  larger  than  is  customary.  The  prevalent  idea  that 
water  is  harmful  when  taken  with  food  because  of  its  action  in 
diminishing  the  secretion  of  gastric  juice,  is  entirely  erroneous.  On 
the  contrary,  water,  even  when  cold,  stimulates  the  gastric  glands, 
and  more  of  their  secretion  is  formed.  To  this  we  shall  recur  in 
discussing  the  process  of  gastric  digestion.  Nor  is  it  true  that 
water  is  "fattening/7  in  the  sense  that  those  who  drink  large 
quantities  necessarily  become  obese.  If  fat  is  "  taken  on  "  by  such 
persons,  it  is  only  because  of  the  indirect  influence  which  water 
exerts  in  keeping  the  nutritive  processes  up  to  a  higher  standard 
and  thus  increasing  assimilation  and  leaving  a  balance  to  be 
stored  up  as  fat.  The  source  of  the  fat  is  not  the  water,  but  the 
carbohydrates  and  other  food-stuffs  Avhich  are  convertible  into  fat. 

Water  being  thus  important — indeed,  essential — great  care 
should  be  taken  to  have  it  free  from  harmful  ingredients.  These 
may  be  inorganic  and  organic. 


122  FOOD. 

The  objectionable  inorganic  constituents  are  those  which  give  to 
the  water  its  "  hardness."  These  are  calcium  carbonate,  to  which 
"  temporary "  hardness  is  due,  and  calcium  chlorid  and  sulphate, 
and  salts  of  magnesium,  which  account  for  "  permanent "  hardness. 
Water  is  not  considered  to  be  "  hard  "  unless  it  contains  more  than 
ten  grains  of  calcium  carbonate  or  its  equivalent  per  gallon  (6.479 
decigrams  per  3.785  liters).  Rain-water  contains  less  than  half  a 
grain  (32.395  milligrams).  To  hard  water  gastric  and  intestinal 
derangements  are  doubtless  attributable,  but  the  evidence  that 
vesical  calculi  or  goiter  are  produced  by  it  is  far  from  convincing. 

It  is,  however,  to  the  organic  impurities  which  drinking-water 
not  infrequently  contains  that  especial  attention  should  be  directed, 
and  more  particularly  to  those  in  the  form  of  disease-germs. 
These  organisms  are  the  undoubted  cause  of  cholera  and  typhoid 
fever,  and  most  probably  of  a  form  of  dysentery  called  "  amebic  " 
or  "tropical."  Each  of  these  diseases  is  produced  by  its  own 
specific  organism  ;  thus,  that  which  produces  cholera  is  Spirillum 
choleras  Asiaticce  ;  that  of  typhoid  fever,  Bacillus  typhosus;  and 
that  of  tropical  dysentery,  Amceba  dysenteries.  These  germs  are 
contained  in  the  stools  of  persons  suffering  from  these  diseases,  and 
their  stools  not  being  disinfected,  the  germs  gain  access  to  drink- 
ing-water either  by  a  leaking  privy-vault  or  in  some  other  way, 
and  those  who  drink  such  water  are  liable  to  become  infected. 
Many  instances  of  epidemics  thus  caused  could  be  cited,  but  one 
must  suffice.  One  of  the  most  striking  epidemics  of  typhoid  fever 
was  that  which  occurred  in  Plymouth,  Pa.,  in  1885.  The  popula- 
tion was  between  8000  and  9000.  Of  this  number,  1153  con- 
tracted the  fever,  and  114  of  these  died.  A  careful  investigation 
showed  that  the  water-supply  of  this  mining-town  had  become  in- 
fected by  the  stools  of  a  single  case  of  typhoid  fever.  These 
stools,  in  an  undisinfected  condition,  had  been  deposited  on  the 
ground  during  the  winter,  and  it  was  not  until  spring,  when  the 
snow  melted  and  warm  showers  occurred,  that  these  infected 
dejecta  were  washed  into  the  water-supply.  The  first  case  occurred 
within  two  or  three  weeks  after.  This  instance  demonstrates  not 
only  the  infecting  power  of  a  single  case  of  disease,  but  also  the 
resisting  power  which  the  typhoid  bacillus  possesses  against  cold, 
for  these  stools  had  been  frozen  for  several  months.  Indeed,  from 
laboratory  experiments  we  know  that  the  Bacillus  typhosus  retains 
its  vitality  even  after  having  been  frozen  for  one  hundred  and  three 
days. 

The  resistance  of  many  other  bacteria  to  low  temperatures  is  a 
well-established  fact.  The  cholera  germ  is  not  killed  at  — 32 c  C. 
(Koch).  The  bacillus  of  tuberculosis  retains  its  vitality  after  an 
exposure  of  forty-two  days  to  the  temperature  of  liquid  air,  — 1 93  C. 
(Swithinbank).  Bacillus  coli  and  other  bacteria  are  not  killed 
after  an  exposure  of  ten  hours  to  the  temperature  of  liquid  hydro- 
gen, —252°  C.  (McFadyen  and  Rowland). 


CARBOHYDRATES.  123 

But,  while  infection  is  not  destroyed  by  freezing,  it  is  by  boil- 
ing, and  there  is  no  surer  way  of  destroying  the  germs  which 
water  may  contain  than  by  boiling  it  for  half  an  hour.  Boiled 
water  is  not  as  unpalatable  as  is  generally  supposed.  Even  if  it 
was,  unpalatability  is  less  objectionable  than  infection,  and  in  all 
doubtful  cases  water  should  be  boiled. 

Another  lesson  to  be  learned  from  this  epidemic  and  from  the 
laboratory  experiments  referred  to  is  that  ice  may  be  a  source 
of  infection  as  well  as  water,  and  even  though  the  water  i»  boiled 
this  will  be  of  no  avail  if  infected  ice  is  used  to  cool  it.  In  ice 
which  was  suspected  of  having  caused  typhoid  fever  at  the  St.  Law- 
rence State  Hospital,  on  the  St.  Lawrence  River,  Hutchings  and 
Wheeler  found  typhoid  bacilli. 

The  writer  investigated  an  epidemic  of  dysentery  in  which  the 
disease  was  traced  to  ice  used  in  drinking-water.  The  ice  had 
been  cut  from  a  pond  in  which  during  the  summer  hogs  wallowed, 
and  in  which  they  deposited  their  excreta..  When  melted  this  ice 
had  a  most  offensive  odor.  Other  instances  might  be  given  show- 
ing the  danger  from  the  use  of  impure  ice,  but  the  one  cited  will 
suffice.  Fortunately,  there  is  now  furnished  for  use  in  many  of 
our  cities  artificial  ice,  which,  if  properly  prepared,  is  free  from 
all  contamination.  In  this  process  of  manufacturing  ice  the  water 
is  not  only  boiled,  but  is  distilled,  and  when  ready  for  freezing  is 
absolutely  pure.  But  even  this  ice  is  not  always  what  it  claims  to 
be.  Unscrupulous  dealers  will  often  supply  river  ice  when  they 
are  supposed  to  deliver  the  artificial  product,  and  manufacturers 
of  the  latter  are  sometimes  careless.  With  boiled  water  and  prop- 
erly manufactured  artificial  ice,  all  danger  of  infection  through 
these  channels  will  surely  be  prevented. 

Salts. — The  list  of  salts  taken  in  with  the  food  has  already 
been  given,  the  most  important  being  sodium  chlorid,  calcium 
phosphate,  and  the  alkaline  carbonates  and  phosphates.  The 
offices  which  these  salts  perform  in  the  economy  of  the  body  vary. 
By  some  of  them  the  solubility  of  certain  ingredients  is  made 
possible,  such  as  the  globulin  of  the  blood  by  virtue  of  the  presence 
of  sodium  chlorid.  From  the  chlorids  the  hydrochloric  acid  of 
the  gastric  juice  is  produced.  Salts  are  stimulants  also  to  the 
glands,  causing  the  latter  to  secrete  more  actively ;  thus  the  diges- 
tive fluids  are  more  abundantly  poured  out  when  the  food  is  prop- 
erly salted,  and  the  kidneys  more  completely  perform  their  .func- 
tions under  the  stimulation  of  the  salts.  If  salts  are  removed 
from  the  food  of  a  pigeon,  it  will  die  in  three  weeks  ;  the  same 
deprivation  of  salts  in  the  case  of  a  dog  will  cause  its  death  in 
six  weeks. 

Carbohydrates. — These  food-stuffs,  in  the  form  of  starch  and 
sugar,  are  especially  abundant  in  vegetable  foods.  They  are  present 
also  in  milk,  but  less  so  in  other  animal  foods. 

Cane-sugar  is  an  article  of  diet  which  is  used  to  an  enormous 


124 


FOOD. 


extent  throughout  the  world.  For  an  exceedingly  interesting  and 
valuable  contribution  to  the  literature  of  this  subject  the  reader  is 
referred  to  Farmers'  Bulletin,  No.  93,  issued  by  the  United  States 
Department  of  Agriculture,  entitled  "  Sugar  as  Food,"  by  Mary 
Hinman  Abel.  From  this  we  have  derived  much  information. 

Between  seven  and  eight  million  tons  of  cane-sugar  are  used 
annually  in  the  different  countries  of  the  world ;  England  con- 
suming in  1895,  86  pounds  per  capita ;  the  United  States,  64 
pounds ;  while  Italy,  Greece,  and  Turkey  consumed  less  than  7 
pounds.  About  two-thirds  of  the  crystallized  sugar  now  used  is  de- 
rived from  the  sugar-beet,  which  has  become  so  developed  that 
while  the  beet  of  1806  contained  but  6  per  cent,  of  sugar,  that  of 
to-day  contains  15  per  cent. 

The  following  table  gives  the  average  composition  of  raw  sugar 
from  different  sources : 

Average  Composition  of  Raw  Sugar. 


Sources  from  which  obtained. 

Water. 

Cane- 
sugar. 

Other  or- 
ganic sub- 
stances. 

Ash. 

Suo'ar-canc 

Per  cent. 
2  16 

Per  cent. 
93  33 

Per  cent. 
4  24 

Per  cent. 
1  27 

Sugar-beet 

2  90 

92  90 

2  59 

2  56 

Sorghum              .        .... 

1  71 

93  05 

4  55 

0  68 

Maize  .    .                .                    .... 

2.50 

88.42 

7  62 

1  47 

Palm     .                    

1.86 

87.97 

9  65 

0  50  ' 

Maple  .               .    . 

82.80 

The  cane-sugar  obtained  from  these  sources  is  identical,  and 
the  popular  opinion  that  beet-sugar  is  not  as  sweetening  and  not 
as  good  a  preservative  as  that  derived  from  the  cane  is  erroneous. 
It  is  a  satisfaction  to  know  that  the  cane-sugar  of  commerce  is  as 
pure  as  is  possible ;  of  five  hundred  samples  examined  by  the 
United  States  Government  chemists,  not  one  was  adulterated. 

The  value  of  sugar  as  food  has  been  abundantly  demonstrated  ; 
its  office  being  to  furnish  energy  to  the  body  in  the  form  of  heat 
and  muscular  work,  in  which  process  it  undergoes  oxidation  and 
becomes  converted  into  CO2  and  H2O  (p.  257).  Experiments  con- 
ducted in  Berlin  and  elsewhere  show  that  sugar  is  "  well  adapted 
to  help  men  to  perform  extraordinary  muscular  labor ;"  and  it  has 
been  used  in  the  German  army  with  such  excellent  results  in  ap- 
peasing hunger,  mitigating  thirst,  and  preventing  exhaustion,  that 
an  increase  of  the  sugar  ration  to  sixty  grams  a  day  has  been 
recommended. 

The  general  conclusions  drawn  by  Abel  in  the  bulletin  above 
referred  to  are  as  follows : 

"  One  may  say  in  general  that  the  wholesomeness  of  sweetened 
foods  and  their  utilization  by  the  system  are  largely  a  question  of 
quantity  and  concentration.  For  instance,  a  simple  pudding- 


FATS  OR   OILS.  125 

flavored  with  sugar  rather  than  heavily  sweetened  is  considered 
easy  of  digestion ;  but  when  more  sugar  is  used,  with  the  addition 
of  eggs  and  fat,  we  have,  as  the  result,  highly  concentrated  forms 
of  food  which  can  be  utilized  by  the  system  only  in  moderate 
quantities  and  which  are  always  forbidden  to  children  and  in- 
valids. 

"  It  is  true  that  the  harvester,  lumberman,  and  others  who  do 
hard  work  in  the  open  air  consume  great  amounts  of  food  contain- 
ing considerable  quantities  of  sugar,  such  as  pie  and  doughnuts, 
and  apparently  with  impunity  ;  but  it  is  equally  true  that  people 
living  an  indoor  life  find  that  undue  amounts  of  pie,  cake,  and 
pudding,  with  highly  sweetened  preserved  fruit,  and  sugar  in  large 
amounts  on  cooked  cereals,  bring  indigestion  sooner  or  later. 

"  From  a  gastronomic  point  of  view  it  would  seem  also  that  in 
the  American  cuisine  sugar  is  used  with  too  many  kinds  of  food, 
with  a  consequent  loss  in  variety  and  piquancy  of  flavor  in  the 
different  dishes.  The  nutty  flavor  of  grains  and  the  natural  taste 
of  wild  fruits  is  concealed  by  the  addition  of  large  quantities  of 
sugar. 

"  In  the  diet  of  the  under-nourished  large  amounts  of  sugar 
would  doubtless  help  to  full  nutrition.  This  point  is  often  urged 
by  European  hygienists.  In  the  food  of  the  well-to-do  it  is  often 
the  case,  however,  that  starch  is  not  diminished  in  proportion  as 
sugar  is  added.  That  sugar  on  account  of  its  agreeable  flavor  is 
a  temptation  to  take  more  carbohydrate  food  than  the  system  needs 
cannot  be  denied.  The  vigor  of  digestion  in  each  particular  case 
would  seem  to  suggest  the  limit.  A  lump  of  sugar  represents 
about  as  much  nutriment  as  an  ounce  of  potato,  but  while  the 
potato  will  be  eaten  only  because  hunger  prompts,  the  sugar,  be- 
cause of  its  taste,  may  be  taken  when  the  appetite  has  been  fully 
satisfied. 

"  Sugar  is  a  useful  and  valuable  food.  It  must,  however,  be 
remembered  that  it  is  a  concentrated  food,  and  therefore  should  be 
eaten  in  moderate  quantities.  Further,  like  other  concentrated 
foods,  sugar  seems  best  fitted  for  assimilation  by  the  body  when 
supplied  with  other  materials  which  dilute  it  or  give  it  the  neces- 
sary bulk. 

"  Persons  of  active  habit  and  good  digestion  will  add  sugar  to 
their  food  almost  at  pleasure  without  inconvenience,  while  those  of 
sedentary  life,  of  delicate  digestion,  or  of  a  tendency  to  corpulency 
would  do  better  to  use  sugar  very  moderately.  It  is  generally 
assumed  that  four  or  five  ounces  of  sugar  per  day  are  as  much  as  it 
is  well  for  the  average  adult  to  eat  under  ordinary  conditions.'' 

Fats  or  Oils. — These  food-stuffs  are  found  in  milk,  in  butter, 
in  cheese,  in  the  fatty  tissues  of  meat,  and  also  in  some  vegetables, 
such  as  nuts.  The  following  table  shows  the  amount  in  some  of 
the  ordinary  foods  : 


126 


FOOD. 


Meat    ;    .    i 5  to  10  per  cent. 

Milk .......  3  to    4    "      " 

Eggs 12  «      " 

Cheese 8  to  30    "      " 

Butter      •  '•-    -^ 85  to  90    u      " 

Proteids. — This  class  contains  some  of  the  most  valuable  of 
the  food-stuffs.  The  importance  of  the  class  is  readily  understood 
when  it  is  recalled  that  the  principal  ingredients  of  the  blood  and 
the  muscles  are  supplied  by  the  proteids  of  the  food.  This  is  the 
only  class  whose  members  contain  nitrogen,  and  it  has  therefore 
been  sometimes  spoken  of  as  the  "  nitrogenous  "  class.  The  albu- 
minoids contain  nitrogen  also,  but  this  class  has  little  nutritive 
value,  except  gelatin,  which  is  valuable,  but,  as  has  already  been 
stated,  its  nitrogen  is  not  available  for  tissue-forming.  The  proteids 
are  represented  in  eggs  by  albumin,  in  milk  by  casein,  in  meat  by 
myosin,  in  peas  and  in  beans  by  legumin,  and  in  the  cereals  by 
gluten.  The  amount  of  proteids  varies  in  different  foods ;  thus 
there  is  in 

Meat 15  to  23  per  cent. 

Milk 3  to    4 

Peas  and  beans      23  to  27 

Grains  (flour) 8  to  11 

Bread       6  to    9 

Potato 1  to    4 

The  following  diagram  (Fig.  85)  shows  the  amount  of  the 
principal  food-stuffs  in  some  of  the  more  generally  used  foods : 


Proteids. 


Fats.        Carbohydrates.        Water. 


Explanation 


Bread 


FIG.  85.— Diagram  showing  proportion  of  the  principal  food-stuffs  in  a  f  w 
typical  comestibles.  The  numbers  indicate  percentages.  Salts  and  indigestible 
materials  omitted  (after  Yeo). 


PROTEWS.  127 

From  the  above  consideration  of  the  food-stuffs  it  is  seen  that 
they  are  in  most  respects  the  same  as  the  tissues  of  the  body ;  yet 
it  would  be  erroneous  to  infer  that  the  fats  and  the  proteids  of  the 
food  go  directly  into  the  tissues  as  such,  and  take  the  place  of  the 
fats  and  the  proteids  which  are  wasted.  There  are  many  inter- 
mediate steps,  some  of  which  are  known  and  will  be  discussed, 
and  others  of  which  we  are  entirely  ignorant.  Experience  has 
abundantly  demonstrated  that  in  order"  to  maintain  the  body  at 
its  physiologic  standard  representatives  from  all  these  four  classes 
of  food-stuffs  must  be  supplied.  If  man  is  deprived  of  water, 
death  speedily  results;  it  comes  as  surely,  though  not  so  quicklv, 
if  fats  or  carbohydrates  or  proteids  are  cut  oif  from  the  food- 
supply.  Indeed,  a  man  may  be  starved  to  death  by  withholding 
the  salts. 

Whenever,  therefore,  it  is  found  that  life  can  be  maintained 
physiologically  for  a  long  period  of  time  on  any  diet,  it  is  certain 
that  this  diet  contains  representatives  of  all  the  classes  enumer- 
ated. Thus,  milk,  which  is  the  sole  food  of  young  children — 
among  some  of  the  Eskimos  to  the  sixth  year  of  life — is  found  on 
analysis  to  contain  such  representatives ;  the  inorganic  class  being 
represented  by  water  and  salts,  the  carbohydrates  by  milk-sugar, 
the  fats  by  butter,  and  the  proteids  by  caseinogen,  lactalbumin,  and 
lactoglobulin.  It  is  not,  however,  sufficient  that  each  class  should 
be  represented,  but  the  proportions  of  the  ingredients  must  be  proper. 
It  is  possible  that  any  given  food  may  have  the  requisite  constituents, 
but  may  have  too  much  of  one  and  too  little  of  another.  It  has  been 
determined  that  the  daily  waste  of  the  body  is  250  to  280  grams 
of  carbon  and  15  to  18  grams  of  nitrogen,  or  about  16  to  1.  The 
carbon  given  off  is  principally  in  the  form  of  carbonic  acid  in  the 
expired  air,  while  the  urea  of  the  urine  contains  most  of  the 
nitrogen  eliminated.  To  supply  the  waste  of  the  body,  then,  the 
proportion  in  the  food  of  carbon  to  nitrogen  should  be  as  16  to  1. 

In  proteids,  however,  the  proportion  is  3.5  to  1,  so  that  should 
proteids  only  be  supplied  to  the  body  there  would  have  to  be  given 
an  enormous  amount  of  nitrogenous  food  in  order  to  supply  enough 
of  the  carbonaceous.  The  effect  of  this  excess  of  nitrogenous 
food  would  be  to  injure  the  digestive  and  eliminating  organs.  So 
that  to  make  up  this  deficiency  of  carbon,  carbohydrates  and  fats 
are  used  in  connection  with  the  proteids.  Imagine,  for  instance, 
the  effect  upon  the  digestive  apparatus  if  man's  exclusive  diet 
was  potatoes.  It  will  be  seen  by  the  table  that  in  potatoes  there 
are  2  per  cent,  of  proteids  and  20.75  per  cent,  of  carbohydrates. 
Therefore,  to  obtain  enough  proteids  from  potatoes  to  sustain  life 
it  would  be  necessary  to  eat  daily  at  least  3.37  kilograms,  or  twenty- 
five  good-sized  potatoes.  In  some  parts  of  the  world  this  has  been 
put  into  practice,  the  effect  being  to  distend  the  stomach  and  to 
derange  digestion  to  a  harmful  degree. 

And  yet  we  must  acknowledge  that  human  life  is  sustained  for 


128  FOOD. 

years  on  a  diet  which  is  far  from  the  standard  here  set  forth. 
Thus  the  Chinaman,  to  obtain  the  nitrogen  necessary,  must  eat 
about  2000  grams  of  rice.  This  gives  him  about  20  grams  of 
nitrogen,  but  700  of  carbon.  Oatmeal  contains  carbon  and 
nitrogen  in  the  proportion  of  15  to  1. 

If  the  diet  was  exclusively  of  meat,  then  in  order  to  supply 
the  body  with  the  necessary  amount  of  carbonaceous  material  a 
very  large  quantity  of  meat  would  be  required,  and  to  meet  this 
requirement  there  would  be  taken  in  an  excess  of  nitrogenous 
constituents,  thus  placing  a  serious  burden  on  the  eliminating 
organs  to  get  rid  of  them.  Experience  demonstrates  that  a  mixt- 
ure of  foods  is  the  true  physiologic  method  of  supplying  the 
wants  of  the  human  body ;  from  meat  are  obtained  the  proteids 
necessary  for  nutrition  ;  from  the  potato  is  derived  the  starch ;  and 
from  butter  is  secured  the  fat.  Experience  shows  also  that  a 
higher  standard  of  efficiency  is  maintained  by  a  variety  of  food, 
a  change  being  made  from  one  kind  of  meat  to  another  and  from 
one  vegetable  to  another,  always,  however,  giving  the  body  the 
food-stuffs  in  the  proper  quantities  to  supply  its  demands. 

There  are  individuals  who  believe  that  meat-eating  is  not  only 
unnecessary  to,  but  that  it  tends  also  to  degrade  man  ;  they  conse- 
quently confine  themselves  to  vegetable  diet :  this  exclusive  dietary 
practice  is  called  "Vegetarianism."  The  vegetarian  movement  has 
become  widespread  both  in  this  country  and  abroad,  and  societies 
with  large  followings  have  been  formed  for  its  propagation  and 
encouragement.  The  grounds  advanced  by  its  adherents  for  its 
support  are  many.  Among  them  are  the  following :  That  the 
character  of  the  human  teeth  is  not  that  of  a  carnivorous,  but  that 
of  a  vegetable  and  fruit-eating  animal ;  that  the  same  is  true  of  the 
intestine,  that  of  man  resembling  very  much  the  intestine  of  certain 
fruit-eating  apes ;  that  there  is  in  a  vegetable  and  fruit  diet  all  that 
man  needs  for  his  sustenance  and  well-being,  and  in  a  more  com- 
pact and  available  form ;  that  many  diseases  which  attack  man, 
such  as  trichinosis,  tuberculosis,  tapeworm,  etc.,  would  be  abolished 
or  at  least  greatly  lessened  if  meat  was  not  eaten.  Other  argu- 
ments relating  to  man's  physical  and  moral  nature  are  adduced  in 
favor  of  vegetarianism. 

The  following  extract  from  a  letter  of  Dr.  Alanus,  a  vegetarian, 
published  in  the  Medical  and  Surgical  Reporter,  gives  his  experi- 
ence and  also  his  opinion  of  vegetarianism  : 

"  Having  lived  for  a  long  time  as  a  vegetarian  without  feeling 
any  better  or  worse  than  formerly  with  mixed  food,  I  made  one 
day  the  disagreeable  discovery  that  my  arteries  began  to  show 
signs  of  atheromatous  degeneration.  Particularly  in  the  temporal 
and  radial  arteries  this  morbid  process  was  unmistakable.  Being 
still  tinder  forty,  I  could  not  interpret  this  symptom  as  a  mani- 
festation of  old  age,  and  being,  furthermore,  not  addicted  to  drink, 
I  was  utterly  unable  to  explain  the  matter.  I  turned  it  over  and 


PROTEIDS.  129 

over  in  my  mind  without  finding  a  solution  of  the  enigma.  I, 
however,  found  the  explanation  quite  accidentally  in  a  work  of 
that  excellent  physician,  Dr.  E.  Monin,  of  Paris.  The  following 
is  the  verbal  translation  of  the  passage  in  question  :  '  In  order  to 
continue  the  criticism  of  vegetarianism  we  must  not  ignore  the 
work  of  the  late  lamented  Gubler  on  the  influence  of  a  vegetable 
diet  on  the  chalky  degeneration  of  the  arteries.  Vegetable  food, 
richer  in  mineral  salts  than  that  of  animal  origin,  introduces  more 
mineral  salts  into  the  blood.  Raymond  has  observed  numerous 
cases  of  atheroma  in  a  monastery  of  vegetarian  friars,  amongst 
others  that  of  the  prior,  a  man  scarcely  thirty-two  years  old,  whose 
arteries  were  already  considerably  indurated.  The  naval  surgeon, 
Treille,  has  seen  numerous  cases  of  atheromatous  degeneration  in 
Bombay  and  Calcutta,  where  many 'people  live  exclusively  on  rice. 
A  vegetable  diet,  therefore,  ruins  the  blood-vessels  and  makes  one 
prematurely  old,  if  it  is  true  that  a  man  is  as  old  as  his  arteries.  It 
must  produce  at  the  same  time  tartar,  the  senile  arch  of  the 
cornea,  and  phosphaturia.'  Having,  unfortunately,  seen  these 
newest  results  of  medical  investigation  confirmed  by  my  own  case, 
I  have,  as  a  matter  of  course,  returned  to  a  mixed  diet.  I  can  no 
longer  consider  purely  vegetable  food  as  the  normal  diet  of  man, 
but  only  as  a  curative  method  which  is  of  the  greatest  service  in 
various  morbid  states.  Some  patients  may  follow  this  diet  for 
weeks  and  months,  but  it  is  not  adapted  for  everybody's  continued 
use.  It  is  the  same  as  with  the  starvation  cure,  which  cures  some 
patients,  but  is  not  fit  to  be  used  continually  by  the  healthy.  I  have 
become  richer  by  one  experience,  which  has  shown  me  that  a  single 
brutal  fact  can  knock  down  the  most  beautiful  theoretic  structure." 

Dr.  Estes,  a  distinguished  American  surgeon,  gives  it  as  his  ex- 
perience that  vegetarians  do  not  stand  the  loss  of  blood  well. 

In  Farmer's  Bulletin,  No.  121,  on  "  Beans,  Peas,  and  other 
Legumes  as  Food,"  issued  by  the  United  States  Department  of 
Agriculture,  the  author,  Mary  Hinman  Abel,  in  comparing  vege- 
table with  animal  protein,  says :  "  It  has  been  well  known  that 
vegetable  foods  without  any  help  from  the  animal  kingdom  will 
sustain  men  in  health  and  working  power,  and  careful  experiments 
have  shown  that  protein  performs  essentially  the  same  part  in  nu- 
trition, whether  it  be  from  milk,  meat,  cereal,  or  legume.  Among 
other  experiments  may  be  mentioned  that  of  Rutger,  a  Dutch 
physician,  and  his  wife,  which  lasted  ten  weeks.  Their  conclusion 
was  that  vegetable  food  can  perfectly  well  be  substituted  for  animal, 
provided  only  that  it  contain  the  same  amount  of  nutrients  in 
proper  proportions.  When  living  on  a  purely  vegetable  diet  they 
relied  largely  on  peas,  beans,  and  lentils,  eating  them  in  some  form 
at  nearly  every  meal.  From  an  economic  standpoint  the  average 
difference  in  the  cost  of  the  two  kinds  of  diet  was  that  less  fuel 
was  used  to  cook  the  animal  foods  eaten.  It  is  not  improbable, 
however,  that  there  are  differences  between  animal  and  vegetable 


130  FOOD. 

protein  that  cannot  be  tested  by  any  method  now  at  our  command, 
differences  which  would  explain  the  almost  universal  preference 
for  some  animal  food  in  the  diet.  From  our  present  knowledge  it 
would  seem  that  a  mixed  diet — of  both  animal  and  vegetable  food — 
is  the  best  and  most  practicable  for  the  vast  majority  of  people." 

In  Physiological  Economy  in  Nutrition,  (p.  139),  Prof.  Chit- 
tenden  says,  "  Man  is  an  omnivorous  animal  and  Nature  evidently 
never  intended  him  to  subsist  solely  on  a  cereal  diet,  or  on  any 
specific  form  of  food  to  the  exclusion  of  all  others.  .  .  .  Vege- 
tarianism may  have  its  virtues,  as  too  great  indulgence  in  flesh 
foods  may  have  its  serious  side,  but  there  would  seem  to  be  no 
sound  physiological  reason  for  the  complete  exclusion  of  any  one 
class  of  food-stuffs,  under  ordinary  conditions  of  life." 

From  the  above  consideration  of  the  subject  we  learn  that  a 
proper  diet  must  contain  not  only  the  various  food-stuffs,  but  must 
contain  them  in  the  proper  proportion.  These  proportions  will 
vary  considerably  according  to  the  age  of  the  individual  and  his 
occupation,  and  also  according  to  the  climate  in  which  he  lives. 
A  glance  at  the  chemical  composition  of  milk,  which  is  the  sole 
food  of  the  infant,  shows  that  the  amount  of  proteids  and  fats  is 
very  much  above  that  in  the  food  of  the  adult. 

Another  factor  to  determine  the  nutritive  value  of  any  food  is 
its  digestibility.  The  chemical  analysis  of  cheese  would  place  it 
high  among  the  foods,  but  experience  shows  that  its  constitution 
is  such  as  not  readily  to  permit  the  action  of  the  digestive  fluids, 
and  its  availability  as  a  food  is  therefore  low. 

The  following  table  represents  a  daily  diet  as  recommended 
by  two  authorities : 

Moleschott.       .  Ranke. 

Proteids 120  grams.  '         100  grams. 

Fats        90      "  100      " 

Carbohydrates      333      "  250      " 

Ranke's  diet,  Avhich  he  regarded  as  sufficient  for  himself,  weigh- 
ing 74  kilos,  corresponds  to  230  grams  of  carbon  and  14  grams 
of  nitrogen. 

While  such  diets  as  these  are  undoubtedly  "  adequate,"  they 
are,  after  all,  to  be  regarded  as  general  averages  only,  to  be  varied 
according  to  the  needs  of  those  for  whose  maintenance  provision 
is  to  be  made.  Thus,  Yoit  (p.  138)  would  supply  to  a  man  weigh- 
ing 70  to  75  kilos,  and  working  ten  hours  a  day,  118  grams  of 
proteid,  56  grams  of  fat,  and  500  grams  of  carbohydrates :  this 
diet  would  give  him  328  grams  of  carbon  and  18.3  grams  of  nitro- 
gen, and  would  have  a  total  fuel-value  of  3000  large  calories. 

Stewart  regards  500  grams  of  bread  and  250  grams  of  lean 
meat  as  a  fair  quantity  for  a  man  fit  for  hard  work.  To  this 
he  adds  500  grams  of  milk,  75  grams  of  oatmeal  in  the  form  of 
porridge,  30  grams  of  butter,  30  grams  of  fat  either  in  the  meat 
or  otherwise,  and  450  grams  of  potatoes.  From  this  would  be 


PEOTEIDS. 


131 


obtained  20  grams  of  nitrogen  and  300  grams  of  carbon,  contained 
in  135  grams  of  proteid,  rather  less  than  100  grams  of  fat  and 
somewhat  more  than  400  grams  of  carbohydrates.  In  the  form 
of  a  table  this  would  appear  as  follows : 


Food. 

Quantity 
in 
Grams. 

Grams  of 

Nitrogen. 

Carbon. 

Proteids. 

Fat. 

Carbo- 
hydrates. 

Salts. 

Lean  Meat  .  .  . 
Bread  
Milk  

250 
500 
500 
30 
30 
450 
75 

8 
6 
3 

1.5 
1.7 

33 
112 
35 
20 
22 
47 
30 

55 
40 
20 

io 

10 

8.5 
7.5 
20 
27 
30 

4 

245  " 
25 

'95   ' 

48 

4 

6.5 
3.5 
0.5 

4.5 
2 

Butter 

Fat  .  
Potato  .... 
Oatmeal  .... 

20.2 

299 

135        97 

413 

21 

The  following  is  the  ration  of  the  English  soldier : 


Bread 680  grams. 

Meat 340      " 

Potatoes 453      " 

Vegetables 226      " 

Milk  .  92      " 


Sugar 37.7  grams. 

Coffee 9.4       " 

Tea 4.6      " 

Salt    .  7 


The  ration  of  the  German  soldier  varies  considerably  from  this  : 

In  war. 

Bread 750  grams. 

Biscuit   .  500 


In  peace. 

Bread 750  grams. 

Meat  150 


Rice 50 

or  Barley  groats     .    .    .      120 

Legumes 230 

Potatoes  .  .1500 


Meat 375 

Smoked  meat 250 

or  Fat 170 

Rice 125 

or  Barley  groats  ....  125 

Legumes 250 


The  following  tables  show  the  net  and  approximate  gross 
weights  of  1000  rations  (and  of  1  ration)  as  usually  issued  by 
the  United  States  Subsistence  Department: 

TABLE  I. — The  "Emergency"  Ration. 


—  .    • 
1000  Complete  Rations. 

Net 
weight. 

Approxi- 
mate gross 
weight. 

Hard  Bread                           .                    

Pounds. 
1000 

Pounds. 
1000 

625 

625 

Pea-meal                                                                 .        

250 

250 

125 

125 

0.58 

0.58 

Salt                     

40 

40 

Pepper,  black  

2.5 

2.5 

Tobacco   plug                                          

31.25 

31.25 

100 

1000  rations  .        .                    

2074.33 

2174.33 

1  ration                                                                        .... 

2.07 

2.17 

132 


FOOD. 


TABLE  II.— The  "Field"  Ration. 


1000  Complete  Rations. 

Net 
weight. 

Approxi- 
mate gross 
weight. 

Bacon         j        

Pounds. 
750 

Pounds. 

883 

Hard  Bread  .       

1000 

1125 

150 

162 

Potatoes,  Onions,  and  Canned  Tomatoes,  when  possible    . 

1000 

80 

1158 

92 

150 

161 

80 

97 

15 

17 

40 

44 

Salt                                   

40 

44 

T*epper,  black   

2.5 

3 

1000  rations 

3307.5 

3786 

1  ration                                                                 •        ... 

3.31 

3.79 

When  flour  is  issued  instead  of  hard  bread,  40  pounds  of  baking-powder  or  dry  yeast. 


TABLE  III. — The  "Travel"  Ration,  used  on  Journeys  by  Railroads, 
Stages,  or  Steamboats. 


1000  Complete  Rations. 

Net 
weight. 

Approxi- 
mate gross 
weight. 

For  first  four  days  : 
Hard  Bread  

Pounds. 
1000 

Pounds. 
1125 

Beef  canned 

750 

875 

Beans   baked    3-pound  cans 

450 

520 

Coffee   roasted 

80 

92 

Susrar 

150 

161 

1000  rations  

2430 

2773 

1  ration  .        

2  43 

2  77 

After  fourth  day  add  : 
Tomatoes  (Ballon  cans)  .        .    .        ... 

1000 

1360 

1000  rations  

3430 

4133 

1  ration  .    . 

3  43 

4  13 

TABLE   IV. — The  "Travel"  Ration  for  Journeys  when   Liquid 
Coffee  is  furnished. 


1000  Complete  Rations. 

Net 
weight. 

Approxi- 
mate gross 
weight. 

Hard  Bread  

Pounds. 
1000 

Pounds. 
1125 

Beef,  canned     

750 

875 

Beans,  baked,  3-pound  cans  

450 

520 

1000  rations  

2200 

2520 

1  ration  

2  2 

2  52 

Twenty -one  cents  per  ration  are  allowed  for  purchase  of  liquid  coffee. 


PROTEIDS. 


133 


TABLE  V. — The  "Garrison"  Ration,  with  the  usual  Proportions 
of  Fresh  and  Salted  Meats  and  Vegetables. 


1000  Complete  Rations. 

Net 
weight. 

Approxi- 
mate gross 
weight. 

Meat: 
Pork   JU 

Pounds. 
75 

Pounds. 
125 

J.    VIJY,      Tff          •         •          ' 

Bacon    ^2(7 

150 

177 

Fresh  Beef,  T7^,  875  Ibs.,  or  fresh  Beef,  750  Ibs.,  and 
Canned  Salmon,  100  Ibs  

Flour 

875 
1125 

-    885 
1507 

Vegetables  : 
Dry     Beans  or  Peas                    .            .                           . 

75 

81 

Or  Rice  or  Hominy          

50 

54 

Fresh—  Potatoes,  800  Ibs.  if  Potatoes    .    .    .    .  700  Ibs. 
Onions  .  200  Ibs.  /      \  Canned  Tomatoes,  300  Ibs. 
Coffee   green     ....        .    .  '  

\   800 
(    300 
100 

808 
350 
122 

Suerar  .                       

150 

161 

Vinegar 

80 

97 

Candles 

15 

17 

Soap                                           ...        

40 

44 

Salt            .                       

40 

44 

Pepper,  black  

2.5 

3 

1000  rations      

3877.5 

4475 

1  ration 

3  88 

4  48 

The  table  on  page  134  shows  the  chemical  composition  and 
nutrient  value  of  these  foods. 

Until  the  Spanish-American  War  the  United  States  had  no 
occasion  to  provide  a  ration  especially  adapted  to  the  soldier  in  the 
tropics,  and  as  a  result  it  is  conceded  that  the  present  ration  is 
inadequate  to  his  needs.  A  court  of  inquiry  appointed  to  investi- 
gate the  character  of  the  food  issued  to  the  troops  during  the  war 
with  Spain  reported  that  "  it  seems  to  be  clearly  established  that 
the  army  ration  as  supplied,  without  modification,  to  the  troops 
serving  in  the  West  Indies,  was  by  no  means  well  adapted  for  use 
in  a  tropical  climate." 

A  most  admirable  essay  on  the  subject  of  "  The  Ideal  Ration 
for  an  Army  in  the  Tropics,"  written  by  Captain  E.  L.  Munson, 
Surgeon  in  the  United  States  Army,  and  to  which  was  awarded  a 
prize,  appeared  in  the  Journal  of  the  Military  Service  Institution  of 
the  United  States  for  May,  1900,  to  which  our  readers  are  referred 
for  an  excellent  and  exhaustive  consideration  of  the  subject  of  diet 
in  hot  countries.  From  this  essay  we  desire  to  make  some  quotations. 

Dr.  Munson  concludes  "  that  the  present  United  States  Army 
ration  is  made  up  of  admirably  selected  articles  in  more  than  suf- 
ficient variety,  and  that  it  is  not  only  wholly  unnecessary,  but 
quite  inadvisable  to  consider  any  nutritive  substances  outside  those 
articles  legally  established  as  components  of  the  food  for  the 
United  States  soldier.  He  thinks,  however,  that  the  proportion 
in  which  these  are  issued  should  be  materially  altered.  The  diet- 
aries which  he  recommends  are  given  on  pages  135  and  136. 


134 


FOOD. 


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Sugar  .... 
or  Molasses  . 

or  Cane  syrup 

PROTEIDS. 


135 


Tropical  Dietary.     I. 


ARTICLES. 

Quantity, 
in  ounces. 

Fats, 
gm. 

Carbo- 
hydrates, 
gm. 

Protein, 
gm. 

Nitrogen, 
gm. 

Fuel-value, 
calories. 

Fresh  Beef  .  . 
Flour  
Beans  .  .  .  . 

10 
18 
2.4 

44.75 

5.60 
1.22 

380.46 
40.18 

41.68 
55.08 
15.16 

6.67 
7.90 
2.42 

590 
1850 
240 

Potatoes  .  .  . 
Dried  Fruit  .  . 
Suo'ar 

16.0 
3.0 
3.5 

0.45 
1.53 

81.70 
33.80 
94.25 

9.50 
1.77 

1.52 
0.27 

380 
220 
397 

.       .       t 

Total  .    .    . 

52.9 

53.55 

630.39 

123.19 

18.78 

3677 

Total  carbon,  395.14  gm.     Nitrogen  to  carbon,  1 :  19.6. 

"  This  table  shows  the  nutrient  value  of  a  proposed  dietary  for 
the  tropics,  containing  the  greatest  amount  of  food-material,  which 
might  be  drawn  by  the  soldier. 

"  The  following  table  shows  a  proposed  dietary  for  the  tropics, 
especially  applicable  to  field  service,  in  which  the  fatty  constitu- 
ents attain  their  maximum  and  the  potential  energy  is  high. 

Tropical  Dietary.     II. 


ARTICLES. 

Quantity 
in  ounces. 

Fats, 
gm. 

Carbo- 
hydrates, 
gm. 

Protein, 
gm. 

Nitrogen, 
gm. 

Fuel-value, 
calories. 

Bacon  .... 
Hard  Bread  .  . 
Beans  .... 
Dried  Fruit  .  . 
Suo~ar  . 

6 
18.  . 
2.4 
3.0 
3.5 

105.06 
6.63 
1.22 
1.53 

371.81 
40.18 
50.70 
94.25 

15.64 
73.12 
15.16 
1.77 

2.49 
11.74 
2.42 
0.27 

1042 

1926 
240 
220 
397 

*       * 

Total  .    .    . 

32.8 

114.44 

556.94 

105.69 

16.92 

3825 

Total  carbon,  328. 76  gm.     Nitrogen  to  carbon,  1  :  23. 

"  The  nutrient  value  of  the  ordinary  dietary  as  proposed  for 
garrison  duty  in  the  tropics  is  as  follows : 

Tropical  Dietary.     III. 


ARTICLES. 

Quantity 
in  ounces. 

Fats, 
gm. 

Carbo- 
hydrates, 
gm. 

Protein, 
gm. 

Nitrogen, 
gm. 

Fuel-value, 
calories. 

Fresh  Beef    .    .  " 
Soft  Bread     .    . 
Potatoes  and  On- 
ions        .    . 
Dried  Fruit  .    . 
Sugar  

10 
20 

16 
3 
3.5 

44.  75 
6.80 

0.72 
1.53 

'299.20' 

73.09 
50.70 
94.25 

41.68 
53.83 

8.60 
1.77 

6.67 
8.61 

1.40 
0.27 

590 
1506 

340 
220 
397 

Total  .    .    . 

52.5 

53.80 

517.24 

105.88 

16.95 

3053 

Total  carbon,  328.76  gm.      Nitrogen  to  carbon,  1  :  18. 


136 


FOOD. 


"  For  the  following  combination  the  several  articles  of  the  ra- 
tion most  closely  approaching  in  character  to  the  food-materials 
used  by  natives  of  the  tropics — proportioned  in  quantity  accord- 
ing to  the  standard  proposed  for  hot  climates — have  been  se- 
lected. 

Tropical  Dietary.     IV. 


ARTICLES. 

Quantity 
in  ounces. 

Fats, 
gin. 

Carbo- 
hydrates, 
gm. 

Protein, 
gm. 

Nitrogen, 
gm. 

Fuel-value, 
calories. 

Fresh  Fish  (cod) 

whole  .    .    . 

14 

0.79 

31.73 

5.07 

120 

Soft  Bread     .    .' 

20 

6.80 

299.20 

53.83 

8.61 

1506 

Rice    

4. 

0.45 

88.87 

8.75 

1.40 

407 

Potatoes  and  To- 

matoes   .    . 

16 

0.54 

65.80 

8.17 

1.36 

297 

Dried  Fruit  .    . 

3 

1.53 

50.70 

1.77 

0.27 

220 

Sugar     .... 

3.5 

.... 

94.25 

I 

341 

Total  .    .    . 

64.5 

10.11 

598.82 

104.25 

16.71 

2947 

Total  carbon,  327.50  gm.     Nitrogen  to  carbon,  1  :  19.6. 

"  On  averaging  these  four  dietaries,  as  furnished  by  the  ration 
proposed  for  the  tropics,  the  mean  nutrient  composition  is  seen  to 
be  as  follows : 


DIETARY. 

Quantity 
in  ounces. 

Fats, 
gm. 

Carbo- 
hydrates, 
gm. 

Protein, 
gm. 

Nitrogen, 
gm. 

Fuel-value, 
calories. 

No.  I. 

No   II 

52.9 
32  9 

53.55 
114  44 

630.39 
556  94 

123.19 
105  69 

18.78  ' 
16  92 

3677 
3825 

No.  III.     .    .    . 
No.  IV.     ... 

52.5 
64.5 

53.80 
10.11 

517.24 

598.82 

105.88 
104.25 

16.95 
16.71 

3053 
2947 

Average     . 

50.7 

57.97 

560.85 

109.06 

17.34 

3375 

Total  carbon,  350  gm.     Nitrogen  to  carbon,  1  :  20. 


"  It  will  be  observed  that  while  the  above  dietaries  differ  con- 
siderably among  themselves,  yet  when  averaged  together  in  equal 
proportions  they  do  not  greatly  vary  from  the  nutritive  standard 
for  the  tropics  already  proposed — and  this  is  an  additional  reason 
why  a  selection  of  the  same  articles  of  the  ration  should  not  be 
made  from  day  to  day.  It  is  seen  that  the  above  average  dietary, 
as  compared  with  the  nutrient  standard,  is  still  slightly  deficient  in 
fats  and  fuel-value  and  a  trifle  in  excess  as  regards  protein.  These 
defects,  if  they  may  be  considered  as  such,  are,  however,  readily 
corrected  by  a  rotation  of  dietaries,  in  which  dietary  II.  is  used 
twice  where  dietaries  I.,  III.,  and  IV.  are  each  employed  but 
once.  The  results  of  this  change  are  as  follows : 


PROTEIDS. 


137 


DlETAEY. 

Quantity 
in  ounces. 

Fats, 
gm. 

Carbo- 
hydrates, 
gm. 

Protein, 
gm. 

Nitrogen, 
gm. 

Fuel-  value, 
calories. 

No  I 

52.9 

53.55 

630.39 

123.19 

18  78 

3677 

No.  II  
No.  II  .... 
No.  III.  .  .  . 
No.  IV.  ... 

32.9 
32.9 
52.5 
64.5 

114.44 
114.44 

53.80 
10.11 

556.94 
556.94 
517.24 
598.82 

105.69 
105.69 
105.88 
104.25 

16.92 
16.92 
16.95 
16.71 

3825 
3825 
3053 
2947 

Average     . 

47.1 

69.43 

572.06 

108.38 

17.26 

3465 

Total  carbon,  363.33  gm.     Nitrogen  to  carbon,  1  :  21. 

"  From  the  above  tables  it  is  evident  that  such  changes  as  are 
advisable  in  the  adaptation  of  the  United  States  Army  ration  to 
tropical  conditions  are  chiefly  in  the  line  of  a  reduction  in  quantity 


ARTICLES. 

Quantity  per  ration, 
ounces. 

*  . 

I- 

1 

1 

Carbohydrates, 
gm. 

§\ 

1! 
P 

Fresh  Beef  (quarters)     
or  Fresh  Mutton 

10.0 
10.0 
6.0 
6.0 
10.0 
10.0 
14.0 

41.68      6.67 
46.201     7.35 
27.54      4.40 
15.64;     2.49 
40.27'     6.44 
45.371      7.26 
31.73      5.07 

44.75 

62.90 
112.54 
105.06 
64.68 
1.13 
0.79 

590 
720 
1093 
1042 
688 
197 
120 

or  Pork 

or  Bacon        .           .    . 

or  Salted  Beef  .           ... 

or  Dried  Fish  (cod)     

or  Fresh  Fish,  average  (whole)     .    . 

Flour  ....        .            .    . 

18.00 
20.00 
18.00 
20.00 

55.00 
53.83 
73.12 
50.40 

7.90      5.60 
8.61i      6.80 
11.74      6.63 
7.99     12.40 

380.46 
299.20 
371.81 
425.80 

1850 
1506 
1926 
1986 

or  Soft  Bread    

or  Hard  Bread  

or  Corn-meal     

Beans 

2.4 
2.4 
4.0 
4.0 

15.16 

16.38 
8.75 
9.20 

2.42 
2.62 
1.40 
1.47 

1.22 
0.75 
0.45 
0.67 

40.18 
41.80 
88.87 
88.75 

240 

246 
407 
430 

or  Peas  .    .                .            .... 

or  Rice   .        .            .    . 

or  Hominy    ... 

Potatoes     
or  Potatoes  80  per  cent,  and  Onions 
20  per  cent  

16.0 
16.0 
16.0 

9.50 

8.60 
8.17 

1.52 
1.40 
1.36 

0.45 
0.72 
0.54 

81.70 
78.09 
65.80 

380 
340 
297 

or     Potatoes     70     per     cent,     and 
Canned  Tomatoes  30  per  cent.  .    . 

Dried  Fruit  (average)     

3.0        1.77 

0.27 

1.53 

35.80 

Sugar     

or  Molasses 

3.5 

Igill 
1  gill 

94.25 
56.05 
56.25 

397 
269 
269 

or  Cane-syrup   

Coflfp.p  ggrppn 

1 

or  Coffee,  roasted     
or  Tea,  green  or  black    

Vinegar 

ft  <sn 

Salt     

Pepper,  black  

Soap    ... 

H 

Candles  

138 


FOOD. 


Protein, 
in  grams. 


Nitrogen, 
in  grams. 


Fats, 
in  grams. 


Carbohydrates 
in  grams. 


Fuel-values, 
calories. 


Standard  dietary  as  given  by  typical  dietaries  of  men 
at  hard  labor  in  the  northern  portion  of  the*  temperate 
zone. 


Standard  dietary  as  given  by  proposed  U.  S.  Army  ration 
for  tropical  service. 


Standard  dietary  for  native  laborers  in  the  tropics ;  based 
on  the  weight  of  145  pounds  for  purposes  of  comparison. 

Standard  dietary  of  the  laboring  class  of  natives  in  the 
tropics  (Java,  British  India,  Guadeloupe,  Abyssinia),  as 
determined  from  the  food  actually  consumed  by  them  at 
normal  body-weights.  • 


of  the  foods  at  present  provided  by  a  too  generous  government. 
It  is  true  that  the  sugars  and  starches  should  be  slightly  augmented, 
but  their  increase  is  small  when  compared  with  the  considerable 
reduction  of  nitrogenous  and  fatty  material  which  is  proposed. 
Many  of  the  components  of  the  present  ration,  as  is  seen  by  the 
above  table,  require  no  change  in  the  consideration  of  the  trop- 


PROTEIDS. 


139 


ical  dietary,  being  not  only  admirably  selected,  but  also  properly 
proportioned." 

The  ideal  ration  for  an  army  of  United  States  soldiers  on  duty 
in  the  tropics  is  therefore  suggested  as  being  of  the  composition 
given  in  the  table  on  page  137. 

Most  valuable,  instructive,  and  revolutionary  are  the  experiments 
•conducted  by  Prof.  R.  H.  Chittenden,  of  the  Sheffield  Scientific 
School,  during  1903,  and  reported  by  him  in  a  book  entitled  Physi- 
ological Economy  in  Nutrition,  published  in  1904.  These  experi- 
ments were  made  on  three  classes  of  men — professional  men, 
soldiers,  and  college  athletes.  We  can  but  give  a  r6sum6  of  the 
most  important  facts  established  by  Prof.  Chittenden,  referring 
our  readers  to  the  book  itself,  with  the  opinion  that  it  is  the  most 
valuable  contribution  on  the  subject  of  which  it  treats  which  has 
been  made  in  recent  years. 

The  experiments  on  the  professional  men  showed  that,  taking 
the  Voit  standard  (p.  130)  as  a  general  average  of  accepted  dieta- 
ries, this  is  entirely  too  generous  for  a  man  whose  occupation  does 
not  involve  excessive  muscular  work,  but  whose  activity  is  mainly 
mental ;  that  such  a  man  can  live  on  a  much  smaller  amount  of 
proteid  or  albuminous  food  than  is  usually  considered  essential  for 
life,  without  loss  of  mental  or  physical  strength  and  vigor,  and 
with  maintenance  of  body  and  nitrogen  equilibrium.  Prof.  Chit- 
tenden himself,  whose  body-weight  was  57  kilos,  showed  for  nearly 
nine  consecutive  months  an  average  daily  metabolism  of  5.7  grams 
of  nitrogen.  His  wants  were  met  by  the  metabolism  of  i33.75 
grams  of  proteid  per  day,  instead  of  the  118  grams  of  Voit.  At 
the  same  time  non-nitrogenous  food  was  much  reduced  below  Voit's 
standard.  A  fuel-value  of  2000  calories  per  day  was  adequate  to 
meet  the  ordinary  wants  of  the  body.  By  experiments  upon  him- 
self and  others  Prof.  Chittenden  has  shown  that  the  minimal  pro- 
teid requirement  for  professional  men  is  from  0.093  to  0.130  gram 
of  nitrogen  per  kilo  of  body-weight.  These  results  were  not 
obtained  on  a  restricted  diet,  each  individual  being  allowed  perfect 
freedom  of  choice.  The  food  of  a  single  day  is  an  illustration  of 
this  : 


Breakfast — 7.45  A.  M. 

Grams. 

Coffee 103 

Cream 30 

Sugar 10 

Lunch— 1.30  P.  M. 

Creamed  Codfish 64 

Potato  balls 54 

Biscuit 44 

Butter 22 

Tea 120 

Sugar 10 

Wheat  griddle-cakes  ...    .  133 

Maple  syrup 108 


Dinner — 6.30  p.  M. 

Grams. 

Creamed  potatoes 85 

Biscuit 53 

Butter     .    .    . 15 

Apples — celery — lettuce  salad  50 

Apple  pie 127 

Coffee 67 

Sugar 8 

Cheese-crackers 17 


140  FOOD. 

The  experiments  with  the  soldiers  showed  that  50  grams  of 
proteid  per  day  were  sufficient  for  the  needs  of  the  body,  and  that 
a  fuel-value  of  2500  to  2600  calories  was  ample  to  meet  their  re- 
quirements. At  the  end  of  the  period  of  training  these  men  were 
in  excellent  condition,  although  in  some  there  was  a  slight  loss  of 
body-weight. 

The  result  of  experiments  upon  the  college  athletes  was  not 
materially  different  from  that  stated  in  connection  with  the  soldiers. 
The  amount  of  nitrogen  excreted  daily  averaged  8.8  grams,  im- 
plying a  metabolism  of  about  55  grams  of  proteid  matter  per 
day. 

Prof.  Chittenden  states  in  conclusion  that  he  can  point  to  vari- 
ous persons  who,  for  periods  varying  from  six  months  to  a  year, 
have  metabolized  daily  5.5  to  7.5  grams  of  nitrogen  instead  of  16 
to  1 8  grams — i.  e.,  they  have  subsisted  quite  satisfactorily  on  an 
amount  of  proteid  food  daily  equal  to  one-third  or  one-half  the 
amount  ordinarily  considered  as  necessary  for  the  maintenance  of 
health  and  strength,  and  this  without  unduly  increasing  the  amount 
of  non-nitrogenous  food ;  that  there  is  marked  increase  in  physical 
strength  as  demonstrated  by  repeated  dynamometer  tests  on  many 
individuals,  which  he  thinks  may  be  ascribed  to  the  greater  freedom 
of  blood  and  lymph,  as  well  as  of  muscle-plasm,  from  nitrogenous 
extractives.  Nor  has  he  been  able  to  find  any  falling  off  in  mental 
vigor,  or  any  change  in  the  hemoglobin-content  of  the  blood,  or 
in  the  number  of  erythrocytes.  He  believes  that  any  excess  of 
food  over  and  above  what  is  needed  imposes  an  unnecessary  strain 
upon  the  organism,  and  especially  upon  the  excretory  organs,  and 
conduces  to  disease,  especially  rheumatism  and  gout. 

Age  is  another  important  factor  which  enters  into  the  problem 
of  the  dietary.  In  early  life,  not  only  must  the  waste  of  the 
tissues  be  met,  but  there  must  be  growth  by  increase  of  tissue. 
In  estimating  the  amount  of  food  to  be  given  to  a  child  as  com- 
pared with  an  adult,  it  is  not  the  weight  of  the  body  which  is  to 
be  taken  into  account,  but  its  surface,  as  it  is  to  this  that  the  waste 
is  proportional.  Thus  a  child  weighing  20  kilos  will  present  a 
body-surface  about  one-half  that  of  a  man  weighing  70  kilos,  and 
it  would  require  therefore  one-half  as  much  food  as  an  adult.  As 
we  have  already  seen,  milk  is,  or  should  be,  the  sole  diet  of  the 
child  up  to  the  age  of  eight  months,  and  in  this  food  we  have  a  diet 
which  contains  twice  as  much  proteid  and  half  again  as  much  fat 
as  the  adult  diet  referred  to  above.  Some  one  has  said  that 
"  The  poorest  mother  in  London  or  New  York  feeds  her  child  as 
if  he  were  a  prince.  Perhaps  not  once  in  a  hundred  times  is  the 
man  as  richly  fed  as  the  young  child,  unless  accident  has  made 
him  a  Gaucho,  or  study  and  reflection  a  gourmand." 

Having  discussed  food-stuffs,  we  will  now  turn  our  attention  to 
some  of  the  more  common  foods  in  which  these  occur. 


HUMAN  MILK. 


141 


MILK. 

As  already  stated,  milk  is  the  sole  food  for  the  developing 
child  during  the  early  months  of  its  existence,  and  indeed,  as 
among  the  Eskimos,  for  a  period  extending  into  years.  It  is 
therefore  a  perfect  food,  inasmuch  as  it  contains  all  that  is  needed 
for  growth  and  the  maintenance  of  the  body  in  a  physiologic  con- 
dition. This  is  true  for  the  early  period  of  life,  but  not  for  the 
later,  as  it  contains  too  little  iron  and  too  much  proteid  and  fat, 
although  adults  have  lived  for  months  on  milk  alone. 

Milk  is  an  emulsion  in  which  the  globules  of  fat  are  sus- 
pended in  a  fluid,  called  milk-plasma.  As  in  other  emulsions, 
so  here,  the  white  color  is  due  to  reflection  of  light  from  the 
globules.  It  is  now  believed  that  the  fat  is  not  enclosed  in  a 
thin  envelope  of  caseinogen,  but  that  by  molecular  attraction  each 
globule  is  covered  by  a  closely  adherent  layer  of  milk-plasma. 
The  diameter  of  the  globules  varies  from  0.0015  to  0.05  mm. 

The  specific  gravity  of  both  cows'  and  human  milk  is  from 
1028  to  1034. 

The  reaction  of  milk  varies  in  different  classes  of  animals. 
In  carnivora  it  is  acid,  but  in  most  other  animals  it  is  either 
slightly  alkaline  or  neutral. 

Milk  contains  the  following 
ingredients,  the  quantity  vary- 
ing in  the  milk  of  different  ani- 
mals :  Water,  caseinogen,  lactal- 
bumin,  lactoglobul in,  lactose,  fat, 
extractives,  as  creatin,  creatinin, 
hypoxanthin,  cholesterin,  and 
traces  of  urea,  salts,  and  the 
gases  oxygen,  nitrogen,  and  car- 
bon anhydrid. 

Human  Milk.— The  first 
milk  secreted  by  the  mammary 

f lands   is    colostrum    (Fig.   86). 
t    is   a   yellowish    liquid,    more  FIG.    86.— Colostrum    and    ordinary 

11     v        *i          .1  .ij  j       milk-globules,    nrst    day    alter    labor; 

alkaline  than  the  milk  secreted  primipara  aged  nineteen  (after  Haskell). 
later  in  lactation,  and  contains 

very  little  caseinogen,  sometimes  none  at  all,  but  lactoglobulin 
and  lactalbumin.  Colostrum  is  regarded  by  some  writers  as 
having  a  distinct  cathartic  action  on  the  newborn  child ;  others 
deny  that  it  possesses  any  such  power.  The  following  table  con- 
tains analyses  by  Clemm  of  human  milk  before  and  immediately 
after  delivery  : 


142 


MILK. 


CONSTITUENTS. 

Four  weeks 
before  delivery. 

Seventeen  days  be- 
fore delivery. 

"8 

e 

o  ^ 

Two  days  after  de- 
livery. 

I. 

II. 

85.2 
14.8 

Water  .... 
Solids  .... 
Casein 

94.52 
5.48 

85.17 
14.83 

85.85 
14.15 

84.38 
15.62 

0.51 

86.79 
13.21 
2.18 

4.86 
6.10 

Albumin  and 
Globulin    .    . 
Fat         .... 
Lactose  .... 
Salts   

2.88 
0.71 
1.73 
0.44 

0.9 
4.1 
3.9 
0.44 

7.48 
3.02 
4.37 
0.45 

8.07 
2.35 
3.64 
0.54 

Lactoglobulin,  which  is  found  in  colostrum,  exists  in  but  very 
minute  amount  in  milk  fully  formed. 

A  comparison  of  the  above  analyses  shows  considerable  varia- 
tion ;  indeed,  such  variation  is  found  in  the  milk  of  the  two 
breasts  of  the  same  woman  and  in  women  of  different  ages. 
Some  authorities  attribute  differences  to  complexion  also. 

The  salts  of  human  milk  are  sodium  lactate,  chlorid,  carbonate, 
phosphate,  and  sulphate  ;  potassium  chlorid  and  sulphate;  calcium 
carbonate  and  phosphate;  magnesium  phosphate;  and  ferric  phos- 
phate. 

In  the  following  table  by  Halliburton  are  given  various 
analyses  of  fully  formed  human  milk:' 


Water. 

Casein-;  Albu- 
ogen.  i   min. 

Fat. 

Sugar. 

Salts. 

Remarks. 

Observers. 

88.58 
90.58 

3.69 
2.91 

3.53 
3.34 

4.3 
3.15 

0.17 
0.19 

9  days  after  delivery. 
12    " 

i  Clemm. 

86.27 

2.95 

5.37 

5.13 

0.22 

Tidy. 

86.3) 
to    }• 

1.68  to  3.15 

(2.6 
«  to 

5.8 
to 

0.23) 
to  >- 

Biel. 

88.8  j 

(5.4 

6.6 

0.34  1 

89.1 

-     1.79 

3.3 

5.4 

0.42 

Gerter. 

87.24 

1.9 

4.3 

5.9 

0.28 

Christenn. 

89.29 
89.06 

1.6 
1.72 

3.2 

2.9 

5.8 
6.0 

0.16 
0.2 

Woman  20-30  years  old. 
"      30-40    " 

|  Pfeiffer. 

87.79 

2.53 

3.9 

5.5 

0.25 

Mendus  de  Leon. 

Cows'  Milk. — The  following  analysis  of  cows'  milk  may  be 
regarded  as  a  sample  of  many  analyses  which  have  been  recorded, 
and  will  enable  a  comparison  to  be  made  with  human  milk. 

Analysis  of  Cows'  Milk  (Simon). 

Water 86.95 

(Win       \ 

Albumin  / 

Fat  (butter) 3.65 

Lactose 4.25 

Inorganic  salts 0.75 


COWS'  MILK.  143 

Comparative  Analyses  of  Human  Milk  and  Cows'  Milk. 

Human  Milk.  Cows'  Milk. 

Water     .    .    . 88.05  .86.95 

Casein  and  albumin 2.45  4.40 

Fat  (butter) 3.40  3.65 

Lactose 5.75  4.25 

Inorganic  salts 0.35  0.75 

If  a  comparison  is  made  between  the  milk  of  the  human  being 
and  that  of  the  cow  it  will  be  seen  that  cows'  milk  contains  more 
proteid,  4.40  as  compared  with  2.45 ;  more  fat,  3.65  to  3.40 ;  and 
more  inorganic  salts,  0.75  to  0.35 ;  but,  on  the  other  hand,  less 
sugar,  4.25  to  5.75.  It  results  from  this  that  in  substituting  cows' 
milk  for  mother's  milk  in  the  feeding  of  infants  the  milk  should 
be  diluted  and  sugar  added. 

In  the  consideration  of  the  carbohydrates  lactose  or  sugar  of 
milk  was  discussed,  so  that  here  we  need  only  refer  to  it.  As  we 
then  learned,  this  variety  does  not  undergo  the  alcoholic  fermen- 
tation with  yeast,  but  does  with  some  other  ferments. 

The  fat  of  cows'  milk  is  a  mixture  of  palmitin,  stearin,  and 
olein,  together  with  triglycerids  of  butyric,  caproic,  and  other  acids. 
It  also  contains  lecithin,  cholesterin,  and  a  yellow  lipochrome.  The 
fats  of  human  milk  differ  somewhat  from  those  of  cows'  milk, 
but  these  differences  are  not  important. 

The  proteids  of  milk  are,  as  already  stated,  caseinogen,  which 
is  by  far  the  most  important,  and  lactalbumin  and  lactoglobulin, 
which  two  are  present  in  but  minute  quantities.  Of  caseinogen 
and  its  properties  we  have  already  spoken. 

It  is  this  constituent  which,  when  milk  coagulates,  becomes 
casein,  forming  with  fat  the  coagulum  or  curd;  the  liquid  portion, 
which  contains  whey-proteid,  lactalbumin,  lactose,  and  salts,  being 
whey.  Milk  is  almost  entirely  free  from  purin  in  any  form  (p. 
434). 

Cows'  milk  is  a  fluid  which  is  very  prone  to  undergo  fermen- 
tative changes ;  one  of  these,  the  formation  of  lactic  acid  from 
lactose,  has  already  been  described ;  but  there  are  others,  which 
are  perhaps  more  harmful,  being  especially  irritating  to  the 
delicate  mucous  membrane  of  the  alimentary  canal  of  the  young 
infant.  These  changes  are  brought  about  by  various  bacteria 
which  find  their  way  into  the  milk  at  the  dairy,  where  the  milk 
is  produced,  or  subsequently,  either  during  transportation  or  after 
it  has  been  delivered  to  the  customer.  Great  pains  should  be 
taken  to  keep  the  surroundings  of  dairy  and  home  in  a  cleanly 
condition. 

Milk  may  be  the  transmitter  of  specific  disease  if  taken  from 
a  diseased  animal — as,  for  instance,  one  suffering  from  tubercu- 
losis ;  and  it  may  also  become  infected  after  coming  from  the  cow 
and  before  it  is  used  as  food.  Numerous  epidemics  of  enteric  or 
typhoid  fever  have  been  traced  to  infection  of  the  milk-supply 


144  MAMMARY  GLANDS. 

by  polluted  water  used  either  to  dilute  the  milk  or  to  wash  the 
cans  which  contained  it ;  scarlet  fever,  also,  has  been  contracted 
by  those  who  have  drunk  milk  which  had  become  infected  by  the 
hands  of  milkers  who  were  recovering  from  the  disease.  Diph- 
theria has  also  been  transmitted  through  infected  milk. 

In  order  to  prevent  the  fermentation  of  milk,  the  bacteria  con- 
tained in  it  should  be  destroyed.  This  may  be  done  either  by 
sterilization  or  pasteurization. 

Sterilization  consists  in  heating  the  milk  to  100°  C.,  the  boiling- 
point,  by  which  the  milk  becomes  " sterile" — that  is,  all  organisms 
which  would  produce  fermentative  changes  in  the  milk  are  killed. 
The  objections  to  this  process  are  that  the  taste  of  the  milk  is 
altered  to  that  of  boiled  milk,  the  casein  is  not  so  easily  digested, 
the  ernulsification  of  the  fat  and  its  absorption  are  not  so  readily 
brought  about,  and  the  amylolytic  enzyme  is  destroyed.  If  the 
exposure  to  the  heat  continues  too  long,  the  milk  becomes  brown- 
ish in  color,  due  to  the  conversion  of  lactose  into  caramel. 

In  pasteurization  the  milk  is  exposed  to  a  temperature  of 
only  71°  C.  to  76°  C.  for  fifteen  to  twenty  minutes;  milk  thus 
treated  is  not  changed  as  in  sterilization,  but  will  keep  only  a  short 
time — a  day  or  two. 

Human  milk  is  the  product  of  the  mammary  glands,  the 
structure  of  which  may  here  be  concisely  described. 

MAMMARY  GLANDS. 

The  mammary  glands  or  mamma3  (Fig.  87)  are  two  in  number, 
situated  one  in  each  pectoral  region.  They  are  compound  racemose 
glands,  and  consist  of  gland-tissue  which  is  made  up  of  lobes,  and 
these  again  of  lobules  (Fig.  88).  The  lobes  are  connected  by 
fibrous  tissue,  and  between  them  is  fat.  Each  lobule  is  composed 
of  sacculated  alveoli  and  a  duct,  the  lobular  duct.  The  lobular 
ducts  discharge  into  larger  ducts,  which  in  turn  discharge  into  a 
lactiferous  duct,  which  may  be  regarded  as  the  excretory  duct  of 
a  lobe.  Of  these  ducts,  tubuli  lactiferi,  there  are  from  fifteen  to 
twenty.  They  open  at  the  surface  of  the  prominent  point  of  the 
breast,  the  mammilla  or  nipple,  surrounding  which  is  the  areola, 
which  in  the  virgin  is  of  a  pinkish  color,  becoming  darker  during 
pregnancy  and  almost  black  at  its  termination.  Under  the  areola 
the  tubuli  lactiferi  are  dilated,  forming  ampullce,  in  which,  during 
the  period  of  lactation,  the  milk  accumulates  in  the  intervals  of 
nursing.  When  these  reservoirs  are  full  the  tension  of  the  gland 
stops  the  process  until  they  are  emptied  by  the  sucking  child, 
when  the  cells  again  take  on  their  function  and  the  milk  is 
secreted  and  flows  into  the  ampullae  through  the  ducts,  there  to 
accumulate  until  the  next  nursing. 


MAMMARY  GLANDS.  145 

The  walls  of  the  alveoli  consist  of  a  basement-membrane, 
covered,  during  the  period  when  the  gland  is  not  active,  by  a  single 
layer  of  flat  or  cuboidal  cells  (Fig.  90)  with  one  nucleus  and 
presenting  a  granular  appearance.  There  are  at  this  time  no  fat- 
globules.  When,  however,  the  gland  begins  to  take  on  an  active 
condition  (Fig.  91)  these  cells  become  higher  and  project  into  the 
interior  of  the  alveoli,  and  the  single  nucleus  divides,  thus  becom- 
ing two.  In  the  cytoplasm  drops  of  fat  appear,  especially  at  the 
ends  of  the  cells  nearest  the  interior  of  the  alveoli,  and  at  the 
same  time  the  nucleus  which  is  nearer  to  this  end  of  the  cell 
becomes  fatty.  This  end  of  the  cell  then  breaks  down,  and  the 


FIG.  87.— Arrangement  of  glandular  tissue  of  breast,  the  fat  having  been  removed 
to  show  the  ducts  and  acini  (Astley  Cooper). 

material  forms  the  albuminous  ingredients  of  the  milk  and  the 
lactose,  while  the  drops  of  fat  become  the  milk-globules.  The 
portion  of  the  cell  which  remains  forms  new  cytoplasm,  and  the 
same  process  is  repeated  over  and  over  again.  The  cells  also 
secrete  water  and  the  salts  which  are  found  in  the  milk. 

There  is  some  difference  of  opinion  as  to  the  origin  of  the 
corpuscles  found  in  the  colostrum,  and  which  are  known  as 
colostrum-corpuscles.  One  view  is  that  they  are  epithelial  cells 
of  the  alveoli,  which  become  rounded  and  in  which  fat  is  devel- 
oped, and  that  in  this  condition  they  become  detached  and  are 
discharged  into  the  cavity  of  the  alveolus.  Another  view  is  that 
10 


146 


MAMMARY  GLANDS. 


they  are  emigrated  lymph-corpuscles ;  while  still  a  third  regards 
them  as  derived  from  the  wandering  cells  of  the  connective  tissue. 
When  the  period  of  lactation  is  over  the  glands  return  approxi- 
mately to  their  original  condition,  thus  undergoing  the  process  of 
involution. 


Clavicle- 


Greater  pectoral - 
muscle. 


Integument- 


Fibrous  septa  con- 
nected with  in- 
tegument. 
Glandular  tissue. 


Mass  of  adipose 
tissue. 


Areola.., 

Interlobular  adi-- 
pose  tissue. 

Nipple. 

Lactiferous  duct.J 

Ampulla. 
Intcrlobular  adi- 
pose tissue. 
Glandular  tissue. 


Peripheral  acini 

Mass  of  adipose 
tissue. 

Fibrous  septa. 
Integument. 


First  rib. 


Second  rib. 

Lesser  pectoral 
muscle. 

Intercostal  mus- 
cles. 


Third  rib. 
Deep  fascia. 


Superficial  fas- 
cia. 

Fourth  rib. 


Horizontal  axis 
of  nipple. 

Fifth  rib. 


Sixth  rib. 


External  oblique  muscle. '• 


FIG.  88. — Longitudinal  section  of  mammary  gland  in  situ;  frozen  subject  of  twenty 

years  (Testut). 

That  the  secretion  of  milk  is  under  the  control  of  the  nervous 
system  there  is  no  doubt,  for  the  instances  are  numerous  in  which 
strong  emotions  of  grief  or  anger  have  caused  the  secretion  to 
cease,  but  just  what  the  relation  is  remains  still  undecided.  It 
may  be  that  secretory  nerves  are  involved  in  the  activity  of  these 
glands,  or  that  it  is  through  the  influence  of  vasomotor  fibers  that 


MAMMARY  GLANDS. 


147 


their  secretion  is  produced ;  but  experiments  have  as  yet  not  de- 
termined the  question.     That  the  glands  may  act  automatically  is 


Duct  and 
alveoli. 


Adipose  tissue. 

FIG.  89. — From  section  of  mammary  gland  of  nullipara  (from  Nagel's  "Die  weib- 
lichen  Geschlechtsorgane,*'  in  Handbuch  der  Anatomic  des  Menschen,  1896). 

proved  by  the  fact  that  when  all  the  nerves  which  supply  them  are 
divided,  the  secretion  still  continues  to  be  formed. 


FIG.  90. — Section  through  the  middle  of  two  alveoli  of  the  mammary  gland  of  the 
dog ;  condition  of  rest  (after  Heidenhain). 

The  table  on  page  149  gives  the  composition  of  milk  and  other 
food-materials,  together  with  their  nutritive  value.  It  is  from  one 
of  the  Farmers'  Bulletins,  "  Milk  as  Food,"  issued  by  the  United 


148  EGGS. 

States  Department  of  Agriculture.     Incidentally  we  would  call 
attention   to   these   publications,  which   are   issued   free   or  at  a 


FIG.  91.— Mammary  gland  of  dog,  showing  the  formation  of  the  secretion: 
A,  medium  condition  of  growth  of  the  epithelial  cells ;  B,  a  later  condition  (after 
Heideuhain).  •  . 

nominal  cost  by  the  Government,  and  are  full  of  practical  value, 
not  alone  to  farmers,  but  to  all  students  of  economics. 

EGGS. 

Eggs  in  various  forms  enter  largely  into  the  common  dietary. 
So  far  as  birds  are  concerned,  eggs  may  be  regarded  as  a  perfect 
food,  inasmuch  as  until  the  young  leaves  the  shell  all  its  nutrition 
has  been  obtained  from  the  shell  and  its  contents,  together  with 
what  it  has  obtained  from  the  atmosphere. 

The  egg  of  the  hen  is  the  one  commonly  used  as  food,  although 
ducks'  eggs  are  eaten  to  a  considerable  extent.  In  a  hen's  egg 
weighing  50  grams  there  are  7  grams  of  shell,  27  grams  of  the 
white,  and  16  grams  of  yolk.  The  yolk  and  white  are  made 
up  of  water,  73.5;  proteids,  13.5;  fats,  11.6  ;  and  salts,  1  per 
cent. 

The  white  of  egg  consists  of  egg-albumin,  egg-globulin,  and 
ovomucoid,  with  some  sugar,  fat,  lecithin,  cholesterin,  and  salts. 

The  yolk  is  composed  of  two  kinds  of  material,  one  yellow, 
containing  fat  and  the  yellow  coloring-matter  lipochrome,  and  the 
other  nearly  white  in  color  in  which  is  found  the  nucleoproteid, 
vitellin,  together  with  sugar,  lecithin,  cholesterin,  and  salts,  as  in 
the  white. 

The  white  of  the  egg  in  its  raw  state  is  more  digestible  than 
when  cooked,  but  there  are  few  persons  to  whom  raw  eggs  are 
palatable.  Egg-albumin  is  coagulated  at  a  temperature  of  73°  C., 
and  vitellin  at  75°  C.  When  the  temperature  reaches  100°  C.,  the 
boiling-point,  and  is  kept  there  for  some  time,  the  albumin  is  so 
thoroughly  and  densely  coagulated  as  to  be  difficult  of  digestion. 

Eggs  have  a  high  nutritive  value,  being  so  rich  in  proteid  con- 
stituents, but  must  be  supplemented  by  carbohydrates,  in  which 
they  are  very  deficient.  They  contain  no  free  purin  or  purin- 
yielding  bodies  (p.  434),  and  are  therefore  useful  when  a  diet  free 


EGGS. 


149 


COMPOSITION  OF   MILK  AND  OTHEE  FOOD-MATERIALS. 

.         Nutritive  ingredients,  refuse,  and  fuel-value. 


Protein.      Fats.       Carbo-     Mineral 
hydrates,  matters. 


Non-nutrients. 


Water.      Refuse. 


Fuel-value. 


Protein  compounds,  e.  g.,  lean  of  meat,  white  of  egg,  casein  (curd)  of  milk,  and 
gluten  of  wheat,  make  muscle,  blood,  bone,  etc. 

Fats,  e.  g.,  fat  of  meat,  butter,  and  oil,  I  serve  as  fuel  to  yield  heat  and  muscular 
Carbohydrates,  e.  g.,  starch  and  sugar,  j          power. 


Nutrients,  etc.,  p.  ct 

Fuel-value  of  1  lb......... 


400       800       1200     1600     2000    2400    2800    3ZOO     3600   4 


150 


MEAT. 


from  purin  is  desired.  Eggs  with  milk  in  which  the  amount  of 
purin  is  very  small,  together  with  butter  and  cheese,  makes  a  diet 
almost  entirely  free  from  purin  free  or  bound. 

MEAT. 

Meat  is  the  flesh  of  such  vertebrate  animals  as  are  used  for 
food,  though  the  term  is  perhaps  commonly  restricted  to  the  mus- 
cular tissue  of  mammals.  It  is  the  kind  of  food  from  which  the 
nitrogen  necessary  for  nutrition  is  chiefly  obtained.  In  meat  there 
are  not  only  connective  and  adipose  tissue,  in  addition  to  muscular 
fiber,  but  even  in  the  leanest  meat  there  are  fat-cells  between  the 
muscular  fibers. 

In  the  following  table  (Munk)  are  given  the  percentages  in 
which  the  various  constituents  occur  in  the  meats  of  the  common 
mammals  used  as  food,  together  with  those  of  fowl  and  pike. 


Constituents. 

Ox. 

Calf. 

Pig. 

Horse. 

Fowl. 

Pike. 

Water    

76.7 

75.6 

72.6 

74.3 

70.8 

79.3 

Solids     
Proteids  and  Gelatin 
Fat     
Carbohydrates     ;    . 
Salts  

23.3 
20.0 
1.5 
0.6 
1.2 

24.4 
19.4 

2.9 
0.8 
1.3 

27.4 
19.9 
6.2 
0.6 
1.1 

25.7 
21.6 
2.5 
0.6 
1  0 

29.2 
22.7 
4.1 
1.3 
1.1 

20.7 
18.3 
0.7 

0.9 
0.8 

We  have  already  discussed  the  chemical  composition  of  muscle 
(p.  62),  and  therefore  need  simply  refer  to  it  here. 

Liebig  states  that  the  flesh  of  young  animals  contains  more 
gelatin  than  that  of  old  ones ;  in  1000  parts  of  beef  there  are  6 
parts  of  gelatin,  while  in  veal  there  are  50  parts.  It  is  a  matter 
of  common  belief  that  veal  is  less  digestible  than  beef.  This 
is,  perhaps,  true  to  some  extent,  but  not  to  such  an  extent  as  is 
generally  thought.  Veal  is  more  tender  than  some  other  meats,  and 
is  therefore  not  usually  well  masticated,  and  hence  not  sufficiently 
prepared  for  the  action  of  the  digestive  juices.  This  renders  its 
digestion  difficult  and  leads  to  the  inference  that  its  digestibility  is 
low.  When  very  young,  veal  has  a  gelatinous  consistency  and  is 
regarded  as  being  unfit  for  food. 

The  cooking  of  meat  has  the  effect  of  making  it  more  digesti- 
ble by  changing  its  collagen  into  gelatin,  and  also  more  palatable. 
Besides  this,  if  the  temperature  is  carried  sufficiently  high,  any 
animal  parasites  or  pathogenic  bacteria  which  the  meat  may  con- 
tain are  killed.  Whenever  meat  is  eaten  which  is  raw  or  in- 
sufficiently cooked,  there  is  always  danger  of  contracting  disease. 
Meat  which  contains  the  Trichina  spiralis  may  in  this  condition 
produce  trichinosis;  and  that  which  contains  cyslicerci  may  cause 
tapeworm  in  those  who  eat  it.  There  is  also  great  danger  from 
eating  the  meat  of  a  tuberculous  animal.  This  is  denied  by  some, 
but  the  evidence  in  its  favor  seems  conclusive  to  the  author. 


MEAT.  151 

Until  the  year  1901  it  was  the  general  consensus  of  opinion 
among  those  who  had  made  a  study  of  the  subject  that  bovine  and 
human  tuberculosis  were  identical.  In  1895,  the  Royal  Commis- 
sion on  Tuberculosis  said :  "  We  find  the  present  to  be  a  conven- 
ient occasion  for  stating  explicitly  that  we  regard  the  disease  as  being 
the  same  disease  in  man  and  the  food  animals,  no  matter  though 
there  are  differences  in  the  one  and  the  other  in  their  manifestations 
of  the  disease ;  and  that  we  consider  the  bacilli  of  tubercle  to  form 
an  integral  part  of  disease  in  each,  and  (whatever  be  its  origin)  to  be 
transmissible  from  man  to  animals,  and  from  animals  to  animals." 

In  1901,  Koch  announced  that  he  felt  "justified  in  maintaining 
that  human  tuberculosis  differs  from  bovine,  and  cannot  be  trans- 
mitted to  cattle."  He  also  expressed  the  opinion  that  bovine  tuber- 
culosis was  scarcely,  if  at  all,  transmissible  to  man.  Since  this 
announcement  of  Koch  was  made,  the  matter  has  been  investigated 
all  over  the  world  by  experienced  and  competent  men,  and  the 
practical  result  of  such  inquiry  is  to  leave  the  subject  where  it  was 
prior  to  Koch's  announcement. 

The  infection  may  not  be  directly  due  to  the  ingestion  of  the 
meat  itself — that  is  to  say,  the  muscular  tissue  may  not  contain  the 
bacilli — but  to  the  tuberculous  matter  from  glands  with  which  in 
the  cutting  of  the  meat  the  butcher  smears  it.  The  Bacillus  tuber- 
culosis is  killed  in  a  few  minutes  at  a  temperature  of  100°  C.,  the 
boiling-point,  in  five  minutes  at  80°  C.,  and  in  four  hours  at  55° 
C.,  but  the  bacillus  itself  must  be  exposed  to  these  temperatures. 
Experiment  has  demonstrated  that  in  ordinary  cooking  both  by 
boiling  and  roasting,  the  temperature  in  the  interior  of  the  joint 
of  meat,  unless  it  is  under  six  pounds  in  weight,  seldom  reaches 
60°  C. ;  and  that  rolled  meat,  in  the  center  of  which  is  tuber- 
culous matter,  is  not  sterilized  by  any  process  of  cooking  if  it 
is  over  four  pounds  in  weight.  It  follows  from  this  that  the 
greatest  care  and  supervision  should  be  exercised  by  health  author- 
ities at  the  slaughter-house,  so  as  to  prevent  the  possibility  of 
infected  meat  finding  its  way  into  the  market.  To  minimize  still 
further  the  danger,  all  meat  which  may  contain  infection  should  be 
thoroughly  cooked. 

The  cysticerci  which  develop  tapeworm  in  man  are  not  destroyed 
by  the  simple  processes  of  salting  and  smoking,  so  that  for  their 
destruction  meat  should  be  exposed  to  a  temperature  of  at  least 
66°  C.,  while  for  the  destruction  of  the  trichina  the  temperature 
should  be  even  higher,  say  70°  C.,  inasmuch  as  the  trichina  is 
enclosed  in  a  capsule  which  serves  as  an  obstacle  to  the  entrance 
of  heat. 

The  common  methods  of  cooking  meat  are,  roasting,  boiling, 
broiling,  and  frying.  These  all  have  their  proper  places,  but 
should  be  employed  with  discrimination.  In  roasting,  the  meat 
is  exposed  to  a  great  heat,  so  as  to  coagulate  the  proteids  on  the 


152  MEAT. 

surface  in  as  short  a  time  as  possible,  thus  retaining  the  juices  of 
the  meat  in  the  interior.  The  temperature  is  then  reduced  to 
93°  C.  or  88°  C.,  and  maintained  at  that  point,  the  general  rule 
being  to  allow  fifteen  minutes  for  every  pound  of  meat,  otherwise 
the  coagulating  process  will  extend  to  the  interior  and  make 
the  muscular  fibers  tough.  This  temperature  is  high  enough  to 
cook  thoroughly  the  whole  piece,  but  not  so  high  as  to  dry  up  the 
juices.  Broiling  is  allied  to  the  process  of  roasting.  In  boiling 
meat  the  same  object  is  accomplished  by  plunging  it  into  boiling 
water,  which  coagulates  the  exterior  as  in  the  roasting  process. 

If,  however,  the  object  to  be  attained  is  to  make  soup  or  broth, 
then  the  meat,  having  been  cut  into  small  pieces,  is  placed  for  some 
time  in  cold  water  and  the  temperature  gradually  raised  to  71°  C. 
By  this  treatment  the  juices  of  the  meat  are  extracted  and  the 
soluble  parts  are  dissolved  out  from  the  meat,  before  the  heat  has 
time  to  coagulate  the  proteid.  It  should  be  remembered,  however, 
that  such  soups  are  not  very  nutritious,  but  are  stimulating.  They 
contain  very  little  proteid  or  fat,  but  do  contain  salts  and  the  ex- 
tractives of  muscles,  such  as  creatin,  creatinin,  etc.  It  is  for  the 
reasons  thus  given  that  beef-tea  is  of  little  value  as  food.  Prof. 
Halliburton,  in  a  recent  address  before  the  American  Chemical 
Society,  called  attention  to  the  valueless  character  of  beef  tea  in  the 
following  language : 

"  Beef  tea,  or  '  beef  extract/  as  it  is  generally  termed  in  the 
United  States,  is  in  no  sense  a  food,  but  merely  a  palatable  and 
stimulating  drink,  ordinarily  harmless,  though  possibly  harmful  in 
gouty  conditions. 

"  I  have  looked  in  vain  among  your  advertisements  for  one 
which  is  familiar  to  us  in  England,  representing  an  ox  in  a  teacup. 
Another  advertisement  on  a  similar  line  shows  an  ox  looking  at  a 
bottle  of  meat  extract  and  saying,  <  Alas  !  my  poor  brother/  the 
inference  being  that  all  that  is  of  nutritive  value  in  the  ox  was  con- 
tained in  the  little  bottle  he  is  contemplating.  The  absurdity  of 
these  advertisements  must  be  apparent  to  all  who  have  any  know- 
ledge of  the  chemistry  of  foods,  and  it  is  the  province  of  the 
physiologist  and  the  chemist  to  teach  the  public  and  the  medical 
profession  how  erroneous  such  views  are.  Instead  of  an  ox  in  a 
teacup,  the  ox's  urine  in  a  teacup  would  be  much  nearer  the  fact, 
for  the  meat  extract  consists  largely  of  products  on  the  way  to  urea, 
which  much  more  nearly  resemble  in  constitution  the  urine  than 
they  do  the  flesh  of  the  ox.  The  manner  in  which  meat  extracts 
have  been  pushed  in  the  market  will,  I  fear,  stand  for  a  long  time 
in  the  way  of  the  recognition  of  the  simple  truth,  that  the  best 
way  of  getting  all  the  available  benefit  from  a  mutton  chop  is  just 
to  eat  it. 

"Some  of  the  manufacturers  of  meat  extracts  have  lately 
awakened  to  the  fact  that  the  general  public  is  learning  something 


CEREALS. 


153 


of  the  real  value,  or  lack  of  value,  of  their  wares,  and,  with  a  view 
to  meeting  the  criticisms  which  have  been  raised,  they  have  added 
greater  or  less  quantities  of  powdered  meat  fibers.  Even  if  it  is 
granted  that  the  powdered  fibers  are  digestible,  and  that  the  meat 
extracts  are  composed  wholly  of  them,  which  they  are  not,  how 
much  nutriment  would  the  patient  receive  from  teaspoonful  doses 
given  through  the  twenty-four  hours  ?  Certainly  not  an  appreciable 
amount." 

If  vegetables  are  added  to  meat  extracts,  making  a  vegetable 
soup,  the  nutritive  value  is  correspondingly  increased.  If  bones 
are  used  in  the  soup-making  process,  the  amount  of  gelatin  may 
be  increased  to  such  an  extent  that  when  cold  the  soup  gelatinizes 
and  becomes  solid. 

Frying  is  a  method  of  cooking  which  should  never  be  applied 
to  meat  such  as  beef,  as  it  makes  it  indigestible  by  reason  of  its 
toughness,  and  also  by  reason  of  the  fat  with  which  it  becomes 
soaked.  If  meats  are  fried  by  immersion  in  boiling  fat,  the 
process  is  not  so  objectionable ;  but  the  fat  should  not  be  allowed 
to  permeate  the  tissue,  as  it  would  do  if  the  process  was  continued 
too  long.  Frying  is  well  adapted  to  the  cooking  of  fish. 

CEREALS. 

The  cereals  are  the  farinaceous  seeds  used  as  food,  such  as 
wheat,  Indian  corn  or  maize,  rice,  rye,  oats,  and  barley.  They 
all  contain  proteids,  fat,  starch,  and  mineral  salts,  though  the  pro- 
portion of  these  ingredients  varies  considerably  in  the  different 
cereals,  as  is  shown  by  the  following  table  (Halliburton) : 


Constituents. 

Wheat. 

Barley. 

Oats. 

Rice. 

Water  
Proteid     

13.6 
12.4 

13.8 
11.1 

13.4 
10.4 

13.1 
7.9 

Fat 

1  4 

2.2 

5.2 

0.9 

Starch  
Cellulose  

67.9 
2.5 

64.9 
5.3 

57.8 
11.2 

76.5 
0.6 

Mineral  Salts  .        ... 

1.8 

2.7 

3.0 

1.0 

The  proteids  in  the  flour  of  cereals  are  not  identical.  Some 
writers  regard  those  in  wheat-flour  as  being  a  vegetable  myosin 
and  a  soluble  proteose  called  phytalbumose.  Gluten,  which  is 
considered  by  some  authorities  as  a  proteid  constituent  of  wheat, 
is  regarded  by  others  as  a  mixture  of  gluten-fibrin,  which  is 
formed  from  the  vegetable  myosin,  and  a  proteose  insoluble  in 
water,  which  is  formed  from  the  phytalbumose,  and  which  gives 
to  the  gluten  its  sticky  consistency.  According  to  this  theory,  the 
gluten  as  such  does  not  exist  until  water  is  added,  when  by  the 
action  of  an  enzyme  gluten  is  produced.  This  enzyme  has,  how- 
ever, never  been  isolated,  and  until  this  theory  is  better  sustained 
by  proofs  we  shall  regard  gluten  as  a  constituent  of  wheat-flour. 


154  CEREALS. 

The  proteids  of  oats  are  three  in  number:  One  soluble  in 
alcohol,  one  a  globulin,  and  the  third  a  proteid  soluble  in  alkali. 

Jn  maize  there  are  two  globulins,  one  a  vitellin  and  the  other 
a  myosin ;  one  or  more  albumins ;  and  zein,  a  proteid  soluble  in 
alcohol. 

The  proteids  of  rye  are  gliadin,  leucosin,  edestin,  and  proteose  ; 
and  those  of  barley  are  leukosin,  proteose,  edestin,  and  hordein. 

The  cereal  most  commonly  used  is,  perhaps,  wheat,  the  flour 
of  which  is  made  into  bread. 

Bread. — The  cereal  most  used  for  bread-making  is  wheat, 
though  bread  is  also  made  from  rye  and  cornmeal.  Wheat-flour 
contains  approximately  14  per  cent,  of  water,  12  of  proteids,  and 
70  of  carbohydrates.  The  amount  of  fat  and  salts  is  small.  In 
the  making  of  flour  the  wheat-grains  are  ground,  and  the  result 
is  sifted,  or  "  bolted  "  as  it  is  termed,  into  fine  flour,  coarse  flour, 
and  bran.  The  bran  is  the  extreme  outer  covering  of  the  grain, 
and  is  so  tough  and  silicious  that  it  is  of  no  nutritive  value,  while 
the  other  coverings  contain  so  much  of  proteid,  fat,  and  salts  as  to 
give  them  considerable  food-value.  The  process  of  making  flour 
just  described  is  known  as  the  old  process,  and  results  in  heating 
the  flour,  which,  if  not  properly  cooled,  is  liable  to  spoil.  In  the 
new  process  the  grains  are  cut  with  knives  or  crushed  between  iron 
rollers  which  do  not  produce  heat.  Flour  is  made  by  another 
process,  in  which  the  grains  are  moistened  and  the  extreme  outer 
covering  or  husks  removed  by  rubbing.  The  grains  after  being 
dried  are  exposed  to  blasts  of  air  which  have  force  enough  to  thor- 
oughly disintegrate  them.  When  pulverized  this  is  known  as 
whole-wheat  flour,  and  contains  all  that  is  nutritive  in  the  wheat. 
In  making  bread  the  flour  is  moistened  with  water  or  milk  to 
which  yeast  has  been  added,  and  when  thoroughly  mixed  this 
becomes  dough.  Salt  is  also  added,  and  some  breadmakers  add 
sugar  and  butter  as  well.  After  thorough  kneading,  the  dough  is 
exposed  to  a  temperature  of  about  24°  C.  The  starch  is  con- 
verted by  an  enzyme  which  exists  in  the  wheat  into  dextrin  and 
sugar,  and  this,  under  the  influence  of  the  yeast,  then  undergoes 
the  alcoholic  fermentation,  alcohol  and  carbonic-acid  gas  resulting. 
This  gas  rises  up  through  the  dough,  expanding  it  to  more  than 
double  its  original  volume,  making  it  thereby  very  spongy.  When 
the  dough  has  risen  sufficiently,  it  is  put  into  an  oven  and  baked. 
This  results  in  killing  the  yeast-cells,  and  thus  prevents  any 
further  fermentation,  and  at  the  same  time  the  carbonic  acid  and 
alcohol  are  expelled  and  the  crust  is  formed.  Wheat  bread  con- 
tains 7  to  10  per  cent,  of  proteids,  55  of  carbohydrates,  1  of  fat. 
2  of  salts,  and  32  to  35  of  water. 


VEGETABLE  PROTEIDS.  155 

VEGETABLES, 

The  green  vegetables  form  a  very  important  part  of  the  food 
of  man.  It  is  true  that  they  contain  a  large  amount  of  water, 
varying  from  75  to  95  per  cent. ;  still,  they  also  contain  carbo- 
hydrates, and  are  one  of  the  principal  sources  from  which  these 
food-stuffs  are  derived.  Thus  in  potatoes,  while  there  is  but  2 
per  cent,  of  proteids,  and  only  0.2  per  cent,  of  fat,  there  is  20  per 
cent,  of  starch.  The  pulses  or  leguminous  plants,  such  as  peas, 
beans,  and  lentils,  supply  man  in  their  seeds  with  food  which  is 
rich  in  proteids  as  well  as  in  carbohydrates ;  thus  in  peas  there  are 

23.7  per  cent,  of  proteid  and  49.3  per  cent,  of  starch ;  in  lentils, 

24.8  per  cent,  of  proteid  and  54.8  per  cent,  of  starch.     The  pro- 
teids of  the  pulses  are  of  the  nature  of  vitellin  and  globulin.     In 
the  kidney-bean  two  globulins,  phaseolin  and  phaselin,  besides 
proteose  have  been  found. 

Vegetable  Proteids. — The  proteids  in  vegetables  may  exist 
in  three  forms:  (1)  In  solution  in  the  juices  of  the  plant;  (2)  in 
the  protoplasm  ;  or  (3)  in  aleurone  grains.  They  are  classified,  as 
are  the  animal  proteids,  into  albumins,  globulins,  albuminates,  pro- 
teoses  and  peptones,  and  coagulated  proteids.  What  was  formerly 
spoken  of  as  legumin  or  vegetable  casein,  or  simply  vegetable 
proteid,  is  now  held  to  be  an  alkali-albumin  produced  by  the 
action  of  the  alkali  used  in  the  extraction  on  the  globulins  which 
exist  normally  in  the  plant.  Proteoses  have  been  found  in  the 
various  varieties  of  flour,  as  well  as  in  the  circulating  fluids  of 
plants,  and  in  the  latter  also  occur  hemi-albumose,  leucin,  tyrosin, 
and  asparagin.  Enzymes  also  exist  in  plants,  and  to  those  of  a 
proteolytic  character  these  proteoses  are  probably  due.  Some 
of  these  proteolytic  enzymes  have  been  carefully  investigated, 
notably  papain  in  the  papaw  plant,  and  bromelin  in  pineapple- 
juice.  In  the  juice  of  the  papaw  are  a  number  of  proteids  :  a 
globulin  resembling  serum-globulin,  an  albumin,  and  two  pro- 
teoses, with  one  of  which  papain  is  associated.  This  enzyme  is 
very  much  like  trypsin. 

Bromelin  acts  in  neutral,  acid,  or  alkaline  media,  acting  particu- 
larly well  at  60°  C.  It  produces  proteoses  and  peptones,  and 
is  used  to  prepare  artificially  digested  foods. 

Enzymes  are  very  abundant  in  the  vegetable  kingdom,  and 
have  for  their  office  the  conversion  of  the  insoluble  proteid  of  the 
seed  into  the  soluble  nitrogenous  substances  of  the  sap.  They 
are,  however,  not  all  of  a  proteolytic  nature.  There  are  also  those 
that  are  amylolytic,  as  the  diastase  in  barley,  and  these  enzymes 
change  the  starch  of  seeds  into  sugar.  Such  a  conversion  we  have 
already  referred  to  in  the  process  of  bread-making  when  the  wheat- 
starch  first  becomes  sugar,  and  then  undergoes  alcoholic  fermenta- 
tion under  the  influence  of  yeast. 


156  BEVERAGES. 

The  nutritious  value  of  fruits  is  not  to  be  overlooked.  When 
fresh  and  ripe  they  are  easily  digested,  and  serve  besides  a  useful 
purpose  in  keeping  the  bowels  in  regular  action. 

BEVERAGES. 

Under  this  general  head  are  included  tea,  coffee,  cocoa,  and 
alcoholic  beverages.  Some  of  these  have  a  distinct  food-value, 
others  are  stimulants  only,  while  the  opinions  held  by  authorities 
as  to  some  of  the  others  are  so  diverse  and  the  results  of  experi- 
ments so  differently  interpreted,  that  it  is  difficult  with  our  present 
knowledge  to  classify  them  with  precision. 

Tea. — Tea  is  an  infusion  made  from  the  leaves  or  leaf-buds 
of  the  tea  plant,  the  principal  constituents  of  which  are  an  aro- 
matic oil,  an  alkaloid,  thein  (C8H10N4O2)  1.8  per  cent.,  tannin 
about  15  per  cent.,  albuminous  compounds,  dextrin,  and  salts  con- 
taining potash  and  phosphoric  acid.  Tea  is  a  stimulant  by  virtue 
of  the  thein  which  it  contains,  and  an  astringent  because  of  the 
presence  of  tannin. 

Tea  should  be  made  with  boiling  water,  and  in  about  five 
minutes  the  infusion  should  be  poured  into  another  vessel ;  if  left 
longer,  it  becomes  bitter  and  unwholesome  because  of  the  large 
amount  of  tannin  dissolved. 

Coffee. — This  beverage  is  an  infusion  made  from  the  seeds 
of  the  coffee  plant.  The  seeds  or  berries  contain  fat,  legumin  or 
vegetable  casein,  sugar,  dextrin,  salts,  an  aromatic  oil,  and  an  alka- 
loid caffein  (C8H10N4O2)  about  0.75  per  cent.,  and  caffeo-tannic 
or  caffeic  acid,  a  variety  of  tannic  acid.  Thein  and  caffein  are 
isomeric,  and  their  effects  are  similar.  While  tea  is  astringent, 
coffee  has  a  laxative  action  on  the  bowels  and  acts  as  a  stomachic 
tonic. 

It  has  also  been  claimed  that  both  tea  and  coffee  act  indirectly 
as  foods  by  retarding  the  waste  of  the  tissues  ;  whether  this  is  true 
or  not,  they  certainly  have  their  uses  in  removing  the  sense  of 
fatigue,  and  they  also  allay  the  sensation  of  hunger.  If  used  to 
excess,  however,  both  coffee  and  tea  disturb  the  digestive  organs 
and  produce  nervous  disturbances,  such  as  headache,  trembling, 
and  wakefulness.  This  condition  is  most  commonly  observed  in 
the  confirmed  tea-drinker,  who  is  as  intemperate  as  anyone  addicted 
to  the  excessive  use  of  alcohol.  Black  coffee  increases  the  heart 
action,  and  is  given  by  physicians  when  the  circulation  is  depressed. 
It  is  also  given  in  cases  of  poisoning  by  opium.  For  its  relation 
to  uric  acid  see  page  434. 

Cocoa. — This  is  prepared  from  the  seeds  of  Theobroma  cacao, 
which  are  roasted,  husked,  and  crushed.  Cocoa-nibs,  as  the 
crushed  seeds  are  called,  contain  about  50  per  cent,  of  oil  or  cocoa- 
butter,  15  per  cent,  of  proteids,  and  an  alkaloid,  theobromin,  0.5 


ALCOHOLIC  BEVERAGES.  157 

to  1.2  per  cent.  This  alkaloid  is  very  similar  in  all  respects  to 
thein  and  caffein. 

Cocoa  is  supposed  to  possess  inuch  more  nutritive  value  than 
either  tea  or  coffee,  and  that  it  is,  therefore,  especially  useful  in 
wasting  diseases,  during  which  it  is  frequently  prescribed,  but 
the  small  amount  of  proteid  and  fat  contained  in  a  single  tea- 
spoonful  of  cocoa  can  hardly  entitle  it  to  a  very  high  place  among 
foods. 

Alcoholic  Beverages. — Under  this  head  are  included  spirits, 
or  those  that  are  distilled ;  wines,  those  that  are  fermented ;  and 
beers  or  malt  liquors. 

Spirits  or  distilled  liquors  include  whiskey,  brandy,  rum,  and  gin. 

Whiskey  is  produced  by  distilling  fermented  grain,  such  as 
corn  or  rye.  It  contains  by  volume  28.90  to  60.30  per  cent.,  and 
by  weight  23.75  to  52.58  per  cent.,  of  alcohol.  Brandy  is  the 
product  of  the  distillation  of  fermented  grapes,  and  has  an  alco- 
holic strength  of  30.80  to  50.40  per  cent,  by  volume  and  25.39 
to  42.96  per  cent,  by  weight.  Brandy  contains  enanthic  and  other 
ethers  which  whiskey  does  not.  These  percentages  are  the  results 
of  actual  analyses  made  by  the  Board  of  Health  of  the  State  of 
New  York,  and  differ  very  markedly  from  those  given  by  most 
authorities.  Thus  we  have  before  us  one  excellent  authority,  who 
states  that  whiskey  contains  44  to  50  per  cent,  by  weight,  or  50  to 
58  per  cent,  by  volume,  of  alcohol ;  and  brandy  39  to  47  per  cent, 
by  weight,  or  45  to  55  per  cent,  by  volume  ;  while  another  makes 
the  statement  that  brandy  contains  from  50  to  60  per  cent,  of 
alcohol.  It  is  evident  from  these  figures  that  the  alcoholic  strength 
of  different  whiskeys  and  brandies  varies  to  a  considerable  degree 
— so  much  so,  indeed,  that  in  using  alcohol  medicinally  physicians 
are  recommended  to  prescribe  "  alcohol  of  a  known  strength, 
flavored  with  ethereal  essences,  and  softened  with  glycerin  or 
syrup"  (Bartley). 

Wines  differ  also  greatly  in  alcoholic  strength,  the  "lighter" 
wines  containing  less,  the  "stronger"  wines  more.  Of  the  lighter 
wines,  champagne  contains  from  5.8  to  13  per  cent.,  and  red 
Bordeaux  6.85  to  13  per  cent. ;  while  of  the  stronger  wines,  port 
contains  from  16.62  to  23.2  per  cent.,  and  sherry  from  16  to  25 
per  cent.  Wines  contain  besides  alcohol  various  aromatic  com- 
pound ethers — enanthic,  citric,  malic,  racemic,  etc. — which  give 
to  them  their  "  bouquet,"  also  sugar,  tannic  acid,  various  other 
acids,  and  potassium  salts. 

Beers  contain  on  an  average  from  3  to  6  per  cent,  of  alcohol 
by  volume ;  although  there  is  here,  as  in  the  distilled  beverages, 
a  great  variation.  They  also  contain  dextrin,  sugar,  lupulin,  free 
organic  acids  and  salts.  Purin-bodies  (p.  434)  have  been  found  in 
beer  and  porter.  Hall  obtained  on  analysis  0.1250  grams  per 
liter  from  lager  beer  and  0.1550  from  porter.  He  remarks  that 


158     EFFECTS  OF  ALCOHOL   UPON  THE  HUMAN  BODY. 

their  presence  may  account  for  the  harmful  influence  of  these  bev- 
erages in  gout,  and  for  some  of  the  pathologic  changes  which 
occur  in  chronic  alcoholism.  In  claret,  sherry,  and  port  no  trace 
of  purin-bodies  is  found.  The  following  table  gives  the  per- 
centages of  alcohol  and  solid  matter  or  extract  in  some  of  the 
common  beers  and  ales  (Allen)  : 


Alcohol. 

Solid  matter 
or  extract. 

Munich  Lae^er  .    .        .        

4.75 

7  08 

Pilsen  Laa;er         .        

3.55 

5  15 

American  La^er  (average  of  19  samples) 

2  78 

6  05 

Bass's  Pale  Ale 

6  25 

6  98 

Alsop's  Pale  Ale                        .... 

6  37 

4  44 

Guinness  's  Stout             .            

6  66 

7  24 

Value  of  Alcoholic  Beverages  as  Food. — It  will  be  seen  that  by 
virtue  of  the  carbohydrates  and  salts  which  wines  and  beers  con- 
tain they  certainly  have  a  food-value  entirely  irrespective  of  the 
alcohol,  which  is  also  one  of  their  constituents.  The  compound 
ethers  are  regarded  as  assisting  digestion  by  promoting  the  secre- 
tion of  the  digestive  fluids,  while  the  bitter  principles  are  well- 
recognized  stomachic  tonics.  Used  in  moderation  they  are  there- 
fore not  injurious,  but  used  to  excess  there  is  danger  of  their 
producing  fat  in  excess,  imperfect  oxidation,  and  a  resulting 
plethoric  and  perhaps  gouty  diathesis. 

EFFECTS  OF  ALCOHOL  UPON  THE  HUMAN  BODY. 

We  come  now  to  consider  a  subject  about  which  volumes  have 
been  written,  and  one  which  has,  perhaps,  excited  more  discussion 
in  both  scientific  and  lay  organizations  than  any  other — i.  e.,  the 
eifects  of  alcohol  upon  the  human  body.  The  warfare  has  raged 
long  and  fierce  around  the  question,  "Is  alcohol  a  food?"  In 
a  discussion  of  any  subject  it  is  very  important  that  there  should 
be  no  misunderstanding  about  the  meaning  of  the  terms  employed, 
and,  therefore,  before  entering  upon  this  discussion  we  must  have 
a  distinct  understanding  as  to  what  is  meant  by  a  food.  For  this 
purpose  we  quote  the  following  definitions  : 

Definitions  of  Food. — "  That  which  is  eaten  or  drunk  for 
nourishment;  aliment;  nutriment  in  the  scientific  sense;  any 
substance  that,  being  taken  into  the  body  of  animal  or  plant, 
serves,  through  organic  action,  to  build  up  normal  structure  or 
supply  the  waste  of  tissue ;  nutriment,  as  distinguished  from 
condi ment." — Standard  Dictionary. 

"  Anything  which,  when  taken  into  the  body,  serves  to  nourish 
or  build  up  the  tissues  or  to  supply  heat." — Borland's  Illustrated 
Medical  Dictionary. 

"  Any  substance,  inorganic  or  organic,  solid  or  liquid,  that  will 


INFLUENCE  OF  ALCOHOL    UPON  GASTRIC  DIGESTION.  159 

nourish  the  body,  renew  the  materials  consumed  in  producing 
those  forms  of  energy  called  vital." — Chapman's  Human  Physi- 
ology. 

"  The  use  of  food  is  to  repair  the  waste  of  the  tissues,  and 
through  combustion  in  the  economy  to  liberate  energy." — Ibid. 

These  quotations  might  be  increased  indefinitely,  but  those 
given  will  answer  our  purpose.  A  food  serves  one  or  more  of  four 
purposes:  1.  To  build  up  normal  structure;  2.  To  dimmish  the 
waste  of  tissue ;  3.  To  supply  the  waste  of  tissue ;  4.  Through 
combustion  (oxidation)  to  liberate  energy.  Any  substance,  there- 
fore, which  performs  any  one  or  more  of  these  four  offices  is  a 
food.  It  may  do  it  to  a  considerable  extent,  and  consequently 
have  great  food-value ;  or  it  may  do  it  to  but  a  slight  extent,  and 
have  but  little  food-value  ;  but  in  so  far  as  it  does  it  at  all  it  is  a 
food. 

Influence  of  Alcohol  upon  Secretion  of  Saliva. — When 
strong  alcohol  or  an  alcoholic  beverage  is  taken  into  the  mouth 
there  is  produced  an  increase  in  the  secretion  of  saliva,  not  only 
as  to  volume,  but  also  as  to  its  organic  and  inorganic  constituents. 
The  same  effect  is  produced  by  vinegar,  ether-vapor,  and  other 
similar  substances.  This  stimulating  effect,  however,  lasts  only 
while  the  liquid  is  in  the  mouth.  Alcohol  in  the  stomach  has  no 
effect  upon  the  secretion  of  saliva. 

Influence  of  Alcohol  upon  Secretion  of  Gastric 
Juice. — The  evidence  is  overwhelming  that  alcohol,  whether 
taken  as  alcohol  or  in  the  form  of  alcoholic  beverages,  such  as 
whiskey,  wine,  or  beer,  increases  the  amount  of  gastric  juice  se- 
creted, and  that  this  is  more  acid  and  contains  more  of  its  normal 
constituents.  The  action  of  this  gastric  juice  upon  proteids  is 
also  very  pronounced.  That  this  is  not  entirely  due  to  direct 
stimulation  of  the  glands  of  the  stomach  by  the  alcohol  is  shown 
by  the  fact  that  when  alcohol  is  introduced  into  the  small  intes- 
tine, and  then  this  latter  is  ligated  so  that  none  of  the  alcohol 
can  enter  the  stomach,  an  increased  secretion  of  gastric  juice  is 
still  produced.  It  is  as  yet  not  determined  just  how  this  is 
brought  about,  whether  by  action  on  the  cells  of  the  gastric  glands 
through  the  medium  of  the  blood,  or  upon  secretory  nerve-fibers. 

It  is  to  be  borne  in  mind  that  other  constituents  than  alcohol 
are  to  be  found  in  wines  and  malted  liquors ;  and  experiments 
show  that  these,  especially  the  organic  acids,  produce  also  a  stimu- 
lating effect  upon  the  gastric  glands,  so  that  the  alcohol  is  not  the 
only  factor  concerned  in  causing  increased  secretion  and  acidity. 

Influence  of  Alcohol  upon  Gastric  Digestion. — In  a 
paper  on  "  Influence  of  Alcoholic  Drinks  upon  Digestion,"  by 
Chittenden,  Mendel,  and  Jackson,  published  in  the  American 
Journal  of  Physiology,  and  to  which  we  are  indebted  for  much 
information,  is  a  synopsis  of  the  opinions  and  results  of  experiments 


160     EFFECTS  OF  ALCOHOL    UPON  THE  HUMAN  BODY. 

of  different  physiologists  on  this  part  of  the  subject.  Kretschy 
observed  in  a  woman  with  gastric  fistula  that  alcohol  retarded 
digestion.  Buchner  found  that  in  the  human  stomach  alcohol, 
wine,  and  beer  retarded  digestion,  but  less  so  than  in  artificial 
digestion.  Bikfavi  observed  in  dogs  a  retardation  of  digestion 
with  even  small  quantities  of  alcohol.  Beer  and  wine  showed  no 
favorable  influence,  the  latter  retarding  digestion  in  large  quanti- 
ties. Ogata  states  that  beer,  wine,  and  brandy  retard  digestion 
noticeably.  Schelhaas  observed  that  in  the  living  stomach  wine 
did  not  retard  digestion  so  long  as  there  was  free  HC1  present. 
Gluzinski  found  that  alcohol  retarded  proteid  digestion  and 
brought  about  the  secretion  of  a  very  active,  strongly  acid  gastric 
juice.  Henczincki  observed  no  bad  effect  on  digestion  with  the 
use  of  beer.  Blumenau  found  that  25-50  per  cent,  alcohol  dimin- 
ishes stomach  digestion  during  the  first  two  or  three  hours.  Wolff- 
hardt  observed  in  a  healthy  man  that  15-20  grams  of  absolute 
alcohol  interfered  with  proteid  digestion ;  that  the  effect  of  cognac 
varied  with  the  period  of  digestion  during  which  it  was  taken ; 
and  that  wines  tended  to  promote  digestion.  Brunton  states  that 
alcohol  increases  the  movements  and  the  secretion  of  the  stomach, 
and  by  mixing  its  contents  more  thoroughly  with  gastric  juice 
accelerates  digestion.  Gluzinski  on  the  other  hand,  finds  that 
alcohol  diminishes  the  mechanical  action  of  the  stomach  to  a 
moderate  degree. 

Chittenden  and  his  associates  experimented  upon  a  dog  to  ascer- 
tain the  effect  of  alcohol  upon  (1)  variations  in  acidity  and  (2) 
time  of  digestion.  The  results  are  very  interesting  and  in- 
structive. 

In  these  experiments  50  grams  of  meat  were  given  in  each, 
sometimes  alone,  sometimes  with  water,  and  sometimes  with 
alcohol  of  varying  strengths,  and  sometimes  with  various  alcoholic 
beverages.  When  meat  alone  was  given  the  stomach  was  empty 
(end  of  gastric  digestion)  in  2  hours  and  55  minutes.  When 
water  was  given  with  the  meat,  the  time  of  digestion  varied  from 
2  hours  and  15  minutes  to  3  hours ;  an  average  of  2  hours  and  40 
minutes.  With  alcohol,  varying  from  22  to  30  per  cent.,  the 
time  was  from  3  hours  to  3  hours  and  45  minutes  ;  average,  3 
hours  and  20  minutes.  With  weak  alcoholic  beverages,  wine  and 
beer,  the  time  of  digestion  was  from  3  hours  to  3  hours  and  15 
minutes ;  average,  3  hours  and  10  minutes.  With  strong  alcoholic 
beverages,  it  was  with  whiskey,  2  hours  in  one  experiment  and  3 
hours  in  another;  with  gin,  3  hours  ;  with  brandy,  2  hours  and  40 
minutes  ;  an  average  of  2  hours  and  40  minutes.  "  The  conclusions 
to  be  drawn  from  these  experiments  would  seem  to  be  that  alcohol 
does  not  retard  proteid  digestion  to  any  great  degree ;  taking  the 
set  of  experiments  quoted  in  connection  with  another  set,  there  is 
a  slight  retardation,  and  that  more  marked  with  malted  beverages. 


ABSORPTION  OF  ALCOHOL  FROM  THE  STOMACH.      161 

Inasmuch,  however,  as  we  have  already  seen,  an  increased  amount 
of  an  active  gastric  juice  is  produced  by  the  alcohol,  it  is  more 
than  probable  that  this  makes  up  for  any  retardation  in  the  pro- 
teolytic  processes. 

The  great  care  with  which  these  experiments  of  Chittenden 
and  his  associates  have  been  made  seems  to  the  writer  to  entitle 
their  conclusions  to  great  consideration,  which  may  be  briefly 
summed  up  in  the  statement  that  "  gastric  digestion  in  the  broad- 
est sense  is  not  markedly  varied  under  the  influence  of  alcohol  or 
alcoholic  fluids.  This  conclusion,  it  may  be  mentioned,  stands  in 
perfect  harmony  with  the  results  of  the  investigations  of  Zuntz 
and  Magnus-Lenz  regarding  the  influence  of  alcohol  (beer)  on  the 
digestibility  and  utilization  of  food  in  the  body.  These  investi- 
gators found  by  a  series  of  metabolic  experiments  on  men  with 
diets  largely  made  up  of  milk  and  bread,  and  on  individuals 
accustomed  and  unaccustomed  to  the  use  of  alcoholic  beverages, 
that  the  latter  did  not  in  any  way  diminish  the  utilization  of  the 
food  by  the  body." 

Influence  of  Alcohol  and  Alcoholic  Fluids  upon  the 
Excretion  of  Uric  Acid. — Beebe  has  conducted  a  series  of 
experiments  reported  by  Chittenden  in  the  American  Journal  of 
Physiology,  with  :  1,  Absolute  alcohol  suitably  diluted  ;  2,  whisky ; 
3,  beer ;  and  4,  port  wine.  The  quantity  used  in  twenty-four 
hours  represented  between  75  and  80  c.c.  of  absolute  alcohol. 
The  result  was  a  marked  increase  in  the  uric-acid  excretion,  the 
increase  in  most  cases  beginning  in  the  second  hour  after  the  meal 
and  reaching  its  height  at  the  fifth  hour ;  this  increase  was  not  due 
to  a  hastening  of  the  normal  output,  but  was  an  actual  increase  in 
the  amount  produced.  The  effect,  Chittenden  believes,  is  doubtless 
due  to  a  disturbance  in  the  metabolism  of  the  purin-bases  of  the 
food  (p.  434).  As  already  stated  (p.  157)  Hall  has  obtained  purin- 
bodies  from  beer  and  porter. 

Absorption  of  Alcohol  from  the  Stomach. — Chittenden's 
experiments,  in  which  200  c.c.  of  37  per  cent,  alcohol  were  intro- 
duced into  the  stomach  of  a  dog  with  the  duodenum  ligated  at 
the  pylorus,  resulted  in  the  complete  disappearance  of  the  alcohol 
in  3-3^-  hours  by  absorption  through  the  stomach-walls  into  the 
blood.  When  the  intestine  is  open  the  absorption  is  more  rapid. 
When  6—8  grams  of  alcohol,  as  wine  or  beer,  are  taken  into  the 
stomach,  80—90  per  cent,  will  have  disappeared  from  the  aliment- 
ary tract  within  ^  hour.  In  one  of  Chittenden's  experiments 
50  c.c.  of  20  per  cent,  alcohol  were  absorbed  within  -J-  hour.  His 
conclusion  is  that,  "  in  view  of  this  rapid  disappearance  of  alcohol 
from  the  alimentary  tract,  it  is  plain  that  alcoholic  fluids  cannot 
have  much,  if  any,  direct  influence  upon  the  secretion  of  either 
pancreatic  or  intestinal  juice." 

We  have  seen  that  when  alcohol  is  taken  into  the  stomach  it 
11 


162     EFFECTS  OF  ALCOHOL    UPON  THE  HUMAN  BODY. 

produces  an  increased  secretion  of  an  active  gastric  juice.  When 
this  stimulation  is  excessive  changes  are  set  up  in  the  mucous 
membrane,  as  a  result  of  which  the  gland  tissue  becomes  less,  and 
the  secretion  is  correspondingly  diminished.  Up  to  the  point 
where  the  stimulation  resulting  in  increase  of  the  normal  secre- 
tion ends  and  the  pathologic  changes  begin,  alcohol  is  not  in- 
jurious, but  manifestly  in  health  no  such  artificial  stimulus  is 
needed.  So  long  as  the  individual  is  well,  the  natural  food  is  a 
sufficient  stimulus  to  the  gastric  glands  and  the  additional  stimu- 
lation of  alcohol  is  uncalled  for,  and  inasmuch  as  the  exact  line 
of  demarcation  between  the  amount  of  alcohol  that  does  good  and 
that  which  does  harm  has  not  as  yet  been  absolutely  determined, 
there  is  always  a  possibility  that  an  excess  may  be  taken  and  in- 
jury result.  So  far  as  the  stomach  is  concerned,  then,  there  is  in 
a  condition  of  health  no  useful  purpose  served  by  alcohol,  but  there 
are  conditions  in  which  this  property  of  alcohol  of  exciting  the 
gastric  glands  to  increased  activity  may  be  availed  of  under 
medical  advice. 

Alcohol  being  a  very  diffusible  substance,  is  mostly  absorbed  by 
the  blood-vessels  of  the  stomach,  which  carry  it  into  the  portal 
vein,  and  by  this  channel  it  reaches  the  liver,  where  its  stimulating 
action  is  again  exercised  upon  the  cells  of  that  organ,  and  an  in- 
creased production  of  bile  is  the  result.  If,  however,  this  stimu- 
lation is  excessive  and  long  continued,  degenerative  changes  take 
place  by  which  the  organ  ultimately  becomes  diminished  in  size 
and  incapable  of  performing  its  function. 

From  the  liver  the  blood  carries  the  alcohol  to  the  heart,  which 
is  quickened  in  action,  and  to  the  brain,  whose  activity  is  also  in- 
creased. If  the  quantity  of  alcohol  is  excessive,  the  cells  of  gray 
matter  in  the  braiii  are  over-stimulated  and  great  excitement  re- 
sults, and  this  may,  if  the  quantity  is  sufficient,  result  in  a  suspen- 
sion of  the  functions  of  the  brain  and  a  condition  of  unconscious- 
ness, passing  on  in  extreme  cases  to  a  fatal  termination.  But  if 
the  quantity  of  alcohol  which  reaches  the  brain  is  not  enough  to 
produce  the  fatal  result,  but  still  enough  to  maintain  the  condition 
of  over-stimulation,  there  result  changes  in  the  structure  of  the 
brain,  as  there  do  in  that  of  the  stomach  and  liver,  which  weaken 
the  mental  activities  and  produce  the  irregular  and  inco-ordinated 
muscular  movements  so  familiar  to  all  who  have  observed  in- 
dividuals who  have  for  years  been  addicted  to  drink. 

From  this  necessarily  incomplete  recital  of  the  effects  of  alcohol 
we  now  turn  to  some  experimental  evidence  bearing  upon  the 
subject.  These  experiments  have  been  carried  on  by  various 
experimenters,  and  some  of  the  results  are  well  summarized  in  the 
following  quotation  from  An  American  Text-Book  of  Physiology 
under  the  title  "  Alcohol  in  the  Body."  "  Alcohol  in  the  stomach 
at  first  prevents  the  gelatinization  necessary  in  proteid  for  peptic 


ABSORPTION  OF  ALCOHOL  FROM  THE  STOMACH.       163 

digestion,  but  this  difficulty  is  of  no  great  moment  because  the 
absorption  of  alcohol  is  rapid  and  complete.  It  makes  the 
mucous  membrane  hypereinic,  promotes  the  absorption  of  accom- 
panying substances  (sugar,  peptone,  potassium  iodid),  and  stim- 
ulates the  flow  of  the  gastric  juice.  In  this  matter  it  acts  as 
do  other  condiments  (salt,  pepper,  mustard,  peppermint),  but  if 
there  be  too  great  an  irritation  of  the  mucous  membrane  there 
is  less  activity  (dyspepsia).  The  rapid  absorption  gives  to  al- 
cohol its  quick  recuperative  effect  after  collapse,  and  its  value 
in  administering  drugs,  especially  antidotes.  Alcoholic  beverages 
combining  alcohol  and  flavor  promote  gastric  digestion  and  absorp- 
tion, but  often  stimulate  the  appetite  in  excess  of  normal  require- 
ments. Alcohol  is  burned  in  the  body,  but  may  also  be  found  in 
the  breath,  perspiration,  urine,  and  milk.  Alcohol  has  no  effect 
on  proteid  decomposition,  but  acts  to  spare  fat  from  combustion. 
The  addition  of  50  to  80  grams  of  alcohol  to  the  food  has  no 
apparent  effect  on  the  nitrogenous  equilibrium.  Alcohol  in  the 
body  acts  as  a  paralyzant  on  certain  portions  of  the  brain,  destroy- 
ing the  more  delicate  degrees  of  attention,  judgment,  and  reflective 
thought,  diminishing  the  sense  of  weariness  (use  after  great  exer- 
tion— furnished  to  armies  in  the  last  hours  of  battle),  and  raising 
the  self-esteem ;  it  paralyzes  the  vasoconstrictor  nerves,  producing 
turgescence  of  the  skin  with  accompanying  feeling  of  warmth,  and 
thereby  indirectly  aiding  the  heart.  Alcohol  acts  to  stimulate  the 
respiration,  especially  in  the  tired  and  weak,  wine  with  a  rich 
bouquet,  like  sherry,  being  more  effective  than  plain  alcohol.  The 
higher  alcohols,  propyl,  butyl,  amyl,  are  more  poisonous  as  the  series 
ascends,  and  are  less  volatile,  less  easily  burned,  and  therefore  more 
tenaciously  retained  by  the  body,  with  more  pernicious  results." 

The  most  complete  and  the  most  recent  knowledge  which  we 
possess  on  the  subject  of  alcohol  and  its  effects  upon  the  human 
body  is  contained  in  a  publication  entitled  "  Physiological  Aspects 
of  the  Liquor  Problem,  Investigations  made  under  the  Direction 
of  W.  O.  Atwater,  John  S.  Billings,  H.  P.  Bowditch,  R.  H.  Chit- 
tenden,  and  W.  H.  Welch,  Sub-Committee  of  the  Committee  of 
Fifty  to  Investigate  the  Liquor  Problem,"  which  was  issued  from 
the  press  in  1903.  The  only  portion  of  this  report  to  which  it  is 
our  purpose  to  here  refer  is  that  which  treats  of  "  The  Nutritive 
Value  of  Alcohol,"  by  Prof.  W.  O.  Atwater.  The  author  states 
at  the  outset  that  no  one  doubts  that  the  continued  and  excessive 
use  of  alcohol  is  injurious  to  body,  mind,  and  character,  and  that 
in  large  enough  quantities  it  is  really  a  poison.  He,  however, 
makes  the  broad  statement  that  the  great  majority  of  physiologists 
and  hygienists  hold  to  the  opinion  that  alcohol,  taken  in  small 
quantities,  may  serve  the  body  for  nutriment,  that  it  is  at  some 
times  valuable,  at  others  harmful. 

The  two  chief  functions  of  food  are,  Prof.  Atwater  states,  to 


164     EFFECTS  OF  ALCOHOL    UPON  THE  HUMAN  BODY. 

furnish  materials  for  the  growth  and  repair  of  the  tissues  and  fluids 
of  the  body  and  to  yield  energy  for  maintaining  the  healthful 
bodily  temperature  and  for  its  muscular  work.  The  proteids  in 
the  main  perform  the  former  function,  and  while  they  also  yield 
energy,  yet  this  is  principally  due  to  the  fats  and  carbohydrates. 
Alcohol,  containing  no  nitrogen,  is  not  a  tissue  builder,  its  value  to 
the  body,  therefore,  if  it  possesses  any,  must  be  that  of  a  fuel,  sup- 
plying energy.  Food  serves  as  fuel  by  being  oxidized  in  the  body  ; 
in  this  oxidation  potential  energy  becomes  kinetic;  part  of  this 
kinetic  energy  appears  as  heat  and  another  part  as  muscular  work. 
Besides,  in  supplying  energy  the  foods  protect  the  body  from  con- 
sumption, for  energy  must  be  produced,  and  if  there  is  nothing  else 
to  produce  it  from,  the  body  tissues  must  undergo  oxidation.  The 
question,  then,  which  Prof.  Atwater  proposed  to  settle  was :  "  Is  the 
energy  of  alcohol  transformed  like  that  of  ordinary  food  materials  ?" 

In  determining  this  question  a  respiration  calorimeter  was  used  ; 
this  served  to  measure  the  materials  received  and  given  off  from 
the  body,  including  the  products  of  respiration,  and  also  to  measure 
the  heat  given  off  by  the  body. 

In  conducting  the  experiments  pure  ethyl  alcohol  was  used, 
generally  to  the  amount  of  two  and  one-half  ounces  a  day,  about 
as  much  as  would  be  contained  in  a  bottle  of  wine  with  10  per 
cent,  alcohol,  or  three  or  four  glasses  (6  or  8  ounces)  of  whisky. 
In  some  of  the  experiments  whisky  or  brandy  was  used.  The 
alcohol  given  was  divided  into  six  doses — three  given  with  meals 
and  three  between  meals — the  object  being  to  avoid  any  special 
influence  of  the  alcohol  upon  the  nerves,  and  thus  test  its  action  as 
food  under  normal  bodily  conditions. 

Without  dwelling  further  upon  the  experiments  we  will  quote 
the  results : 

1.  Alcohol  in  moderate  amounts  tended  to  very  slightly  increase 
the  digestibility  of  the  protein,  but  did  not  materially  alter  the 
digestibility  of  the  other  nutrients.     While  this  is  the  statistical 
result  of  these  experiments,  the  extent  to  which  it  would  be  true 
in  general  experience  is  by  no  means  certain. 

2.  In  the  average  of  the  experiments  at  least  98  per  cent,  of  the 
alcohol  taken  was  actually  oxidized  in  the  body.     Other  experi- 
ments show  that  in  ordinary  diet  about  98  per  cent,  of  the  carbo- 
hydrates, 95  per  cent,  of  tlie  fats,  and  93  per  cent,  of  the  protein 
are  burned  in  the  body.     Accordingly,  the  alcohol  is  more  com- 
pletely oxidized  than  are  the  nutrients  of  an  ordinary  mixed  diet, 

3.  The  law  of  the  conservation  of  energy  obtained  with   the 
alcohol  diet  as  with  the  ordinary  diet.     The  potential  energy  of  the 
alcohol  oxidized  in  the  body  was  transformed  completely  into  kinetic 
energy  and  appeared  either  as  heat  or  as  muscular  work,  or  both. 
To  this  extent,  at  any  rate,  it  was  used  like  the  energy  of  the  pro- 
tein, fats,  and  carbohydrates  of  the  food. 


ABSORPTION   OF  ALCOHOL  FROM  THE  STOMACH.       165 

4.  Fat  protection  in  the  alcohol  rations  was  very  slightly  dif- 
ferent from  that  with  the  ordinary  rations ;   in  other  words,  the 
alcohol  was  practically  as  efficient  in  the  protection  of  body  fat  from 
consumption  as  the  fats  or  carbohydrates  of  the  food  which  it  re- 
placed. 

5.  The  power  of  alcohol  to  protect  the  protein  of  food  or  body 
tissue,  or  both,  from  consumption   is    clearly  demonstrated.     Its 
action  in  this  respect  appears  to  be  similar  to  that  of  the  carbo- 
hydrates and  fats ;  that  is  to  say,  in  its  oxidation  it  yields  energy 
needed  by  the  body,  and  thus  saves  other  substances  from  oxidation. 

6.  Alcohol  appears  to  exert  at  times  a  special  action  as  a  drug. 
In  large  quantities  it  is  positively  toxic  and  may  retard  or  even 
prevent  metabolism  in  general,  and  proteid  metabolism  in  particular. 
In  small  doses  it  seems  at  times  to  increase  the  disintegration  of 
protein.     The  only  justification  for  calling  alcohol  a  proteid  poison 
is  found  in  this  disintegrating  tendency. 

7.  In  some  of  the  experiments  alcohol  was  administered  with 
coffee,  in  others  with  water.     There  was  no  direct  evidence  that 
the  coffee  interfered  with  the  action  of  the  alcohol ;  if  any  effect 
was  produced,  it  was  to'  increase  rather  than  retard  proteid  met- 
abolism. 

8.  When  72  grams  of  alcohol,  given  in  six  doses  and  furnishing 
500  calories  of  energy,  replaced  the  isodynamic  amounts  of  fats  and 
carbohydrates,  the  alcohol  caused  no  considerable  increase,  in  the 
amount  of  heat  radiated  from  the  body.     If  the  alcohol  had  all 
been  taken  at  one  dose,  it  might  have  caused  the  cutaneous  vessels 
to  dilate,  possibly  stimulated  the  sweat-glands,  increased  the  cir- 
culation, and  thus  increased  the  heat  radiation.    If  enough  alcohol 
had  been   taken   to   induce   the   comatose  condition  called  "  dead 
drunk/'  and  if  the  men  experimented  upon  had  been  exposed  at 
the  same  time  to  severe  cold,  the  production  of  heat  in  the  body 
might  have  been  retarded  and  the  radiation  increased  so  as  to  lower 
the  body  temperature  by  several  degrees. 

9.  In  the  experiments   alcohol  was  not   suddenly  or  /rapidly 
oxidized,  or  if  there  was  such  rapid  oxidation,  there  was  a  correspond- 
ing decrease  in  the   oxidation  of  carbohydrates,  fats,  or  protein. 
The  alcohol,  carbohydrates,  and  fats  replace  one  another  as  sources 
of  energy  ;  as  either  was  oxidixed,  the  others  were  proportionately 
spared. 

10.  In  all  the  test  experiments  alcohol  was  certainly,  and  in  the 
work  experiments  it  was  in  all  probability,  a  source  of  heat  for  the 
body. 

11.  The  hypothesis  that  alcohol  contributed  its  share  of  energy 
for  muscular  work  is  natural  and  extremely  probable,  but  not  ab- 
solutely proved.     Even  with  the  small  doses  in  these  experiments 
there  were  indications  that  the  subjects  worked  to  slightly  better 
advantage  with  the  ordinary  rations  than  with  the  alcohol.     The 


166     EFFECTS  OF  ALCOHOL   UPON  THE  HUMAN  BODY. 

results  of  practical  tests  on  a  large  scale  elsewhere  coincide  with 
those  of  general  observation  in  implying  that  the  use  of  any  con- 
siderable quantity  of  alcoholic  beverages  as  part  of  the  diet  for 
muscular  labor  is  generally  of  doubtful  value  and  often  positively 
injurious. 

In  closing  the  consideration  of  the  question  "  Is  alcohol  food  ?" 
Prof.  Atwater  says  :  "  If  I  may  be  permitted  the  expression  of  a 
personal  opinion  it  is  that  people  in  health,  and  especially  young 
people,  act  most  wisely  in  abstaining  from  alcoholic  beverages,  but 
I  cannot  believe  that  the  cause  of  temperance  in  general,  or  the 
welfare  of  the  individual,  is  promoted  by  basing  the  physiologic 
argument  against  the  use  of  alcohol  on  anything  more  or  less  than 
attested  fact." 

If,  with  the  results  of  these  experiments  in  mind,  we  now  turn 
back  to  the  definition  of  food,  we  shall  see  that  alcohol  is  a  food. 
We  have  dwelt  to  a  considerable  extent  upon  this  subject  for  the 
reason  that  many  of  the  text-books  used  in  the  grammar  and  high- 
schools  of  the  country  deal  with  the  effects  of  alcohol  upon  the 
human  body  by  reason  of  laws  which  have  been  enacted  requiring 
them  so  to  do.  Unfortunately,  many  of  these  books  do  not  repre- 
sent the  physiologic  facts  as  we  believe  them  to  be.  The  ten- 
dency of  these  books,  to  say  the  least,  is  to  teach  that  alcohol  is 
not  a  food,  but  a  poison.  That  it  is  a  food  we  think  has  been 
abundantly  proved ;  that  it  is  a  poison  is  also  true,  but  whether  it 
is  the  one  or  the  other  depends  upon  the  amount  taken.  There 
are  many  things  which,  in  certain  quantities,  are  not  only  not 
harmful,  but  are  absolutely  essential.  The  process  of  stomach 
digestion  requires  that  the  gastric  juice  should  contain  hydrochloric 
acid,  and  normally  this  is  present  to  the  amount  of  0.2  per  cent., 
and  yet  given  in  a  sufficiently  large  quantity  it  would  produce 
death. 

The  experiments  of  Prof.  Atwater  and  his  colleagues  mark  a 
new  era  in  the  history  of  this  most  important  subject,  the  effect 
of  alcohol  upon  the  human  body  ;  and  in  all  future  discussions 
arguments  should  not  be  based  upon  the  experiments  which  pre- 
ceded theirs,  unless  they  were  conducted  with  similar  precaution?. 


III.    NUTRITIVE  FUNCTIONS. 


DIGESTION. 

HAVING  considered  the  composition  of  the  body  and  food,  there 
may  now  be  taken  up  the  study  of  the  nutritive  functions. 

As  has  been  noted  already,  the  body  is  constantly  producing 
energy  and  undergoing  waste,  both  of  which  require  the  taking  of 
food.  But  food  is  of  absolutely  no  use  to  the  body  until  it  reaches 
the  blood  and  by  this  fluid  is  conveyed  to  the  tissues.  So  long  as 
the  food  remains  within  the  alimentary  canal  it  is  as  much  out- 
side the  body,  so  far  as  nutrition  is  concerned,  as  if  it  had  never 
been  taken  inside.  To  be  of  any  service  the  food  must  enter  the 
blood,  and  it  does  this  by  being  absorbed. 

In  some  forms  of  animal  life  the  food  is  of  such  a  nature  that 
it  readily  and  without  further  change  undergoes  absorption — that 
is,  passes  through  the  walls  of  the  absorbing  vessels.  In  other 
forms  of  animal  life  this  is  not  the  case :  in  the  latter,  unless 
certain  changes  take  place,  the  food  passes  out  of  the  alimentary 
canal  as  waste  material,  without  having  contributed  to  the  nutri- 
tion of  the  body  in  the  slightest  degree.  Unless,  therefore,  some 
provision  was  made  to  obviate  this,  such  animals  would  die  of 
starvation.  The  provision  which  has  been  made  consists  in  the 
presence  of  certain  organs  whose  duty  is  to  change  the  form  of 
the  food-substances  from  that  in  which  they  will  not,  into  that  in 
which  they  will,  be  absorbed ;  and  into  such  forms  that  when  they 
reach  the  tissues  they  can  be  utilized  by  them.  It  is  this  prepara- 
tion for  absorption  which  constitutes  digestion,  and  the  organs 
concerned  in  bringing  about  the  necessary  changes  in  the  food  are 
the  digestive  organs. 

Manifestly,  these  organs  will  be  simple  or  complex  according 
to  the  amount  of  change  which  it  is  necessary  to  bring  about  in 
the  food  in  order  that  absorption  may  take  place.  Thus,  if  the  food 
on  which  an  animal  relies  for  its  sustentation  is  already  in  a  proper 
form,  no  change  will  be  needed,  and  the  animal  will  therefore  have 
no  digestive  organs.  If  the  requisite  change  is  a  slight  one,  the 
number  of  the  digestive  organs  will  be  few  and  their  structure 

167 


168 


DIGESTION 


will  be  simple.  But  if  the  food  is  varied  in  its  composition,  and 
largely  made  up  of  food-stuffs  that  require  many  changes  before 
they  are  fitted  for  absorption  or  before  they  can  be  utilized  by  the 


Nose. 


Submaxillary 

and  sublingual 

glands. 

Trachea. 


Liver. 
Gall-bladder. 


Duodenum. 


Large  intestine. 


Vermiform  appendix 


Parotid  gland. 


Pharynx. 
Vein. 


Thoracic  or 

chyle  duct. 
Esophagus. 


Small  intestine. 


Anus. 


FIG.  92.— General   scheme  of  the  digestive  tract,  with  the  chief  glands  opening 

into  it. 


tissues  after  they  are  absorbed,  then  the  digestive  apparatus — that 
is,  the  group  of  organs  concerned  in  digestion — will  be  complex. 
Such  is  the  character  of  the  food  of  man,  and,  consequently,  such 
is  the  character  of  his  digestive  apparatus  (Fig.  92). 

The  human  digestive  apparatus  consists  of  the  alimentary  canal 
and  the  other  digestive  organs,  which,  although  outside,  still  com- 
municate with  this  canal  by  ducts  through  which  their  secretion 
is  poured.  The  alimentary  canal  consists  of  the  mouth,  the 
esophagus,  the  stomach,  and  the  small  intestine.  The  digestive 
organs  which  are  outside,  but  which  discharge  their  secretion 


MOUTH  DIGESTION.  169 

into  this  canal,  are  the  salivary  glands,  the  liver,  and  the  pan- 
creas. 

The  digestive  process  is  subdivided  into  three  parts  :  That 
which  takes  place  in  the  mouth — mouth  digestion;  that  which 
takes  place  in  the  stomach — stomach  or  gastric  digestion  ;  and  that 
which  takes  place  in  the  small  intestine — intestinal  digestion.  For- 
merly, when  digestion  was  spoken  of  it  was  always  stomach  diges- 
tion which  was  referred  to,  because  it  was  supposed  that  the  entire 
process  took  place  in  that  organ ;  and  when  digestion  was  impaired 
the  remedies  which  physicians  employed  were  directed  to  the 
stomach  alone.  There  is,  unfortunately,  too  much  of  this  kind 
of  practice  even  now ;  but  the  study  of  physiology  has  taught 
that  indigestion  may  be  due  quite  as  much  to  the  improper  per- 
formance of  mouth  and  intestinal  digestion  as  to  that  which 
takes  place  in  the  stomach,  and  unless  this  is  recognized  many 
cases  will  be  unsuccessfully  treated. 

When  food  is  taken  into  the  mouth  it  has,  presumably,  been 
as  fully  prepared  as  possible  by  the  removal  of  those  portions 
which  are  of  no  nutritive  value.  No  one  eats  the  husks  of  corn, 
the  shells  of  nuts,  the  gristle  of  meat,  or  similar  substances,  be- 
cause experience  has  shown  that  they  are  of  little  or  no  nutritive 
value,  and  that  their  digestion  is  practically  impossible.  Such 
extraneous  matters,  therefore,  are  removed,  and  the  food  is  further 
prepared,  provided  this  preparation  is  necessary,  by  the  process 
of  cooking.  In  the  form,  then,  in  which  the  food  is  taken  in  it 
is  as  fully  prepared  as  it  can  be  outside  the  body.  Whatever 
remains  to  be  done  in  order  that  the  food  may  be  prepared  for 
absorption  must  be  effected  after  it  enters  the  alimentary  canal. 

Some  of  the  ingredients  of  human  food  are  already  in  a  con- 
dition to  be  absorbed  by  the  blood-vessels  of  the  alimentary  canal, 
and  therefore  they  need  to  undergo  no  change.  Such  ingredients 
are  water,  salts,  and  dextrose  ;  and  were  they  the  only  constituents 
of  the  food,  no  digestive  organs  would.be  needed  ;  but,  as  already 
said,  this  is  not  the  fact.  The  greater  part  of  the  food  must  be 
changed  before  it  can  be  absorbed.  The  first  step  in  this  conver- 
sion is  that  which  takes  place  in  the  mouth. 


MOUTH  DIGESTION. 

When  food  enters  the  mouth  it  consists  of  a  mixture  of  vari- 
ous food-stuffs.  In  order  that  the  changes  which  these  food-stuffs 
undergo  may  be  traced  thoroughly,  let  it  be  supposed  that  repre- 
sentatives of  all  classes  of  food-stuffs  are  present,  namely,  (1) 
inorganic,  salts  and  water ;  (2)  carbohydrates,  starch  and  sugar ; 
(3)  fats,  or  oils ;  and  (4)  proteids. 

All  the  food  of  a  fluid  nature,  no  matter  what  classes  of  food- 


170 


MOUTH  DIGESTION. 


stuffs  it  comprises,  passes  immediately  from  the  mouth  into  the 
pharynx,  and  thence  through  the  esophagus  into  the  stomach. 


FIG.  93. — Schema  showing  the  temporary  and  permanent  teeth  in  a  child  five 
years  old  (right  side):  1,  temporary  teeth  of  the  upper  jaw;  2,  the  five  temporary 
teeth  of  the  lower  jaw ;  3,  3',  permanent  median  incisors;  4,  4',  permanent  lateral 
incisors;  5,  5',  permanent  canines;  6,  6',  the  four  permanent  bicuspids;  7,  7',  first 
molar;  8,  second  molar  of  lower  jaw  in  its  alveolus  (in  the  upper  jaw  the  second 
molar  is  not  yet  formed) ;  9,  inferior  dental  canal ;  10,  orifice  of  inferior  dental 
canal  (after  Testut). 

Such  food  undergoes  no  chemical  changes  whatever  during  this 
time ;  thus,  milk,  chocolate,  and  beverages  of  various  kinds  are 
unchanged.  If,  however,  fluids  are  taken  into  the  mouth  when  it 
contains  solid  food,  the  latter  will  be  softened  by  them,  and  the 


Bicuspids     Canine      Incis 


Bicuspids    Canine  Incisors 


FIG.  94.— Schema  of  the  two  dental  arches ;  view  of  their  external  faces,  showing 
their  natural  relations. 

two  will  be  mixed,  and  will  come  under  the  influence  of  the  agents 
concerned  in  carrying  on  mouth  digestion.  These  agents  are  the 
teeth  and  the  salivary  glands. 


MASTICATION. 


171 


Mastication. — The  chewing  of  the  food  or  mastication  is 
performed  by  the  teeth. 

The  first  set  of  teeth,  which  are  known  as  temporary,  decidu- 
ous, or  milk-teeth  (Fig.  93),  and  which  exist  during  early  child- 
hood are  twenty  in  number,  and  the  second  or  permanent  set 
(Fig.  95),  which  begin  to  take  the  place  of  the  first  set  at  about 
the  sixth  year  of  life,  remain  to  a  greater  or  lesser  extent  until 
old  age.  The  latter  set  is  composed  of  thirty-two  teeth — four 
incisors,  two  canines,  four  bicus- 
pids, and  six  molars — in  each  jaw 
(Fig.  95).  The  incisors,  or  cut- 
ting teeth,  are  adapted  to  bite  the 
food  ;  the  molar  teeth,  or  grinders, 
are  adapted  to  grind  the  food,  while 
the  canines  and  bicuspids  in  man 
aid  the  incisors  and  molars.  In 
the  carnivora,  the  canines — or 
tushes  as  they  are  called — are 
very  long  and  pointed,  and  are 
admirably  adapted  to  pierce  the 
body  of  their  prey,  even  to  the 
vitals,  thus  killing  and  subse- 
quently tearing  the  animal  pre- 
paratory to  feeding  upon  it.  The 
herbivora  need  no  such  aggres- 
sive weapons,  and  in  them  the 
molars  are  so  constructed  as  to 
grind  the  food,  their  teeth  resem- 
bling the  grindstones  of  the  mil- 
ler. The  teeth  of  man  have  char- 
acters which  resemble  those  of 
both  carnivora  and  herbivora,  and 
from  this  fact  it  may  be  inferred 
that  it  was  designed  that  man 
should  have  a  mixed  diet. 

Movements  of  Mastication. — 
The  movements  concerned  in 
mastication  are  those  of  the  lower  jaw  upon  the  upper,  produced 
by  the  action  of  the  following  muscles :  Masseter,  temporal, 
internal  and  external  pterygoids,  digastric,  mi/lohi/oid,  and  genio- 
hyoid.  The  lower  jaw  is  brought  against  the  upper  by  the  con- 
traction of  the  masseters,  temporals,  and  internal  pterygoid  mus- 
cles. The  action  of  the  external  pterygoids,  when  both  are 
acting,  is  to  draw  the  lower  jaw  forward,  causing  it  to  project 
beyond  the  upper.  If  but  one  external  pterygoid  acts,  that  side 
of  the  jaw  is  drawn  forward  and  the  chin  deviates  to  the  oppo- 
site side. 


FIG.  95. — The  palate  and  superior 
dental  arch  (right  side)  :  1,  median 
incisors ;  2,  lateral  incisors  ;  3,  canine ; 
4,  first  bicuspid;  5.  second  bicuspid; 
6,  first  molar;  7,  second  molar;  8, 
wisdom-tooth  ;  9,  mucous  membrane 
of  the  hard  palate  continuous  behind 
with  that  of  the  soft  palate ;  10,  the 
anteroposterior  raphe  of  palate  ;  11, 
pits  on  each  side  of  the  raphe  per- 
forated with  the  orifices  of  glands; 
12,  anterior  rugosities  of  the  mucous 
membrane  (after  Testut). 


172  MOUTH  DIGESTION. 

The  digastric,  rnylohyoid,  and  geniohyoid  muscles  depress  the 
lower  jaw,  and  this  is  an  essential  part  of  mastication,  for  the 
jaws  must  be  separated  as  well  as  brought  together  to  make  the 
act  complete. 

The  movements  of  the  jaw  are  a  combination  in  which  these 
muscles  act,  sometimes  grouped  in  one  way  and  sometimes  in 
another.  The  buccinator  muscles  in  the  cheeks  and  the  muscles 
of  the  tongue  assist  very  materially  by  keeping  the  food  between 
the  teeth,  where  it  may  be  comminuted  and  triturated. 

The  function  of  the  teeth  in  man  is  to  subdivide  and  com- 
minute thoroughly  the  food  ;  and  this  function  is  an  essential  part 
of  the  process  of  digestion.  As  will  be  seen  later,  during  diges- 
tion certain  fluids  are  poured  into  the  alimentary  canal  to  contrib- 
ute their  part  toward  the  process.  These  fluids  cannot  act 
properly  on  large,  compact  masses  of  food.  While  their  action  is 
not  that  of  solution,  still,  in  order  to  fulfil  perfectly  their  office, 
they  must  come  in  direct  contact  with  every  portion  of  the  food. 
This  contact  is  the  more  essential  because  the  given  time  in  which 
to  act  is  not  unlimited,  and  if  the  process  is  not  completed  within 
the  allotted  time,  digestion  will  be  performed  incompletely. 
When  a  chemist  desires  to  dissolve  a  substance  quickly  and  com- 
pletely, he  first  pulverizes  it  in  a  mortar.  Likewise,  in  digestion 
one  of  the  most  important  steps  is  this  process  of  comminution 
or  mastication.  If  mastication  is  insufficiently  performed,  the 
succeeding  steps  in  the  process  of  digestion  are  seriously  interfered 
with,  and  indigestion  or  dyspepsia  results.  f 

Insufficient  mastication  is  one  of  the  commonest  causes  of  in- 
digestion, and  many  dyspeptics  are  drugged  with  remedies  pre- 
scribed to  overcome  some  fancied  trouble  in  the  stomach,  wjien 
they  should  be  sent  to  a  dentist.  Defective  mastication  may  be 
due  to  various  causes.  The  teeth  may  be  so  decayed  as  to  expose 
sensitive  surfaces,  and  when  food  which  is  at  all  hard  is  taken  into 
the  mouth  the  discomfort,  or  sometimes  the  pain,  caused  their 
possessor  in  chewing  it  makes  the  performance  of  the  act  incom- 
plete, and  the  food  is  swallowed  half-masticated ;  or  the  eater  may 
be  in  too  great  a  hurry  and  not  give  enough  time  to  this  important 
act.  Whatever  the  cause,  the  result  is  the  same;  therefore  too 
much  attention  cannot  be  given  to  this  process,  which  is  so  simple 
as  often  to  be  overlooked. 

Insalivation. — Coincident  with  mastication  is  the  act  of  in- 
salivation  or  the  incorporation  of  saliva  with  the  food.  Saliva  is 
the  mixed  secretion  of  the  salivary  glands,  which  comprise  the 
two  parotids,  the  two  submaxillaries,  and  the  two  sublinyuals, 
together  with  the  buccal  glands  of  the  mucous  membrane  of  the 
mouth  (Fig.  96). 

Physiologic  Anatomy  of  the  Salivary  Glands. — The  parotid 
gland  is  the  largest  of  all  the  salivary  glands,  and  is  named  from 


INSALIVATION. 


173 


its  proximity  to  the  ear,  lying  below  and  in  front  of  it.  Inflam- 
mation of  this  gland  is  parotitis  or  mumps.  Its  secretion  passes 
out  by  Stenson's  duct,  which  is  about  6  cm.  long  and  the  size  of 
a  crowquill,  and  is  discharged  into  the  mouth  on  the  inner  surface 
of  the  cheek,  opposite  the  second  molar  tooth  of  the  upper  jaw. 


FIG.  96.— View  of  the  salivary  glands  (right  side)  (the  inferior  maxilla  has  been 
removed  from  the  symphysis  to  the  ascending  ramus) :  A,  parotid  gland,  with  A' 
its  anterior  prolongation ;  B,  submaxillary  gland ;  C,  sublingual  gland ;  7),  gland 
of  Niihn  or  of  Blandin ;  E,  gland  of  Weber,  a,  duct  of  Steno ;  6,  duct  of  Wharton 
with  b'  its  orifice  on  the  floor  of  the  mouth  ;  c,  excretory  ducts  of  the  sub- 
lingual  gland.  1,  sternocleidomastoid  ;  2,  posterior  belly  of  the  digastric;  3,  3', 
mylohyoid,  right  and  left ;  4,  hyoglossus ;  5,  genioglossus ;  6,  pharyngoglossus ;  7, 
geniohyoid  muscle;  8,  masseter ;  9,  buccinator;  10,  middle  constrictor  of  the 
pharynx;  11,  primitive  carotid;  12,  internal  jugular  vein;  13,  external  carotid 
artery ;'  14,  lingual  artery  ;  15,  facial  artery ;  16,  facial  vein ;  17,  superficial  tem- 
poral artery ;  18,  transverse  facial  artery ;  19,  facial  nerve ;  20,  auriculotemporal 
nerve ;  21,  lingual  nerve,  displaced  slightly  upward  on  account  of  the  position  of 
the  tongue. 

The  nerves  which  supply  this  gland  are  branches  of  the  carotid 
plexus  of  the  sympathetic,  the  facial,  the  auriculotemporal,  and 
the  great  auricular  nerve. 

The  submaxillary  gland  is  situated  beneath  the  lower  jaw.     Its 
secretion  is  discharged  by  Wharton' *s  duct,  which  is  about  5  cm. 


174 


MOUTH  DIGESTION. 


long  and  opens  at  the  side  of  the  frenum  of  the  tongue.  Its 
nerves  come  from  the  submaxillary  ganglion,  and  consist  of  fila- 
ments of  the  chorda  tympani  of  the  facial  and  lingual  branch  of 
the  inferior  maxillary,  of  the  mylohyoid  branch  of  the  inferior 
dental,  and  of  the  sympathetic. 

The  sublingual  gland  lies  under  the  mucous  membrane,  at  the 
side  of  the  frenum  of  the  tongue.  Its  secretion  is  discharged 
through  from  eight  to  twenty  ducts,  ducts  of  Rivinus,  which  open 
on  the  prominence  of  the  mucous  membrane  made  by  the  gland 
beneath.  Sometimes  two  or  more  of  these  ducts  join,  and  form 
the  duct  of  Bartholin,  which  opens  into  Wharton's  duct.  The 
nerves  of  this  gland  are  branches  of  the  lingual. 

Besides  these  three  sets  of  glands  there  are  numerous  mucous 
glands  on  the  dorsum  and  the  edges  of  the  tongue,  in  the  tonsil, 
and  the  soft  palate,  whose  secretion  is  a  constituent  of  the  saliva. 
The  salivary  glands  belong  to  the  class  ordinarily  described  as 
compound  racemose  glands.  Inasmuch,  however,  as  the  secreting 
portions  are  not  sacs,  which  are  characteristic  of  racemose  glands, 
but  tubes,  this  variety  of  gland  is  perhaps  better  denominated 
compound  tubular.  It  consists  of  lobes,  which  in  turn  are  made 
up  of  lobules,  each  of  which  is  composed  of  tubular  alveoli  or 
acini  connected  with  a  duct.  The  ducts  from  different  lobules 
join  together  to  form  larger  ducts,  and  finally  all  combine  to  form 
the  main  duct  of  the  gland. 

Mucous  (Fig.  97)    and  Albuminous   Glands. — Two  types  of 

glands  are  recognized 
by  histologists  accord- 
ing to  the  product  and 
the  appearance  of  the 
cells  within  the  alveoli 
of  the  salivary  glands  : 
mucous  and  albuminous 
or  serous. 

The  mucous  gland 
secretes  a  tenacious  fluid 
containing  mucin,  and 
the  cells  are  relatively 
large  and  clear,  and 
have  been  described  as 
resembling  ground 
glass ;  their  granules 
are  ordinarily  indistinct. 
The  sublingual  and  the  mucous  glands  of  the  mouth  are  repre- 
sentatives of  this  type. 

These  glands  also  contain  demilunes  of  Heidenhain  or  crescentic 
cells,  which  are  placed  between  the  mucous  cells  and  the  base- 
ment-membrane (Fig.  97).  Heidenhain,  whose  name  they  bear, 


FIG.  97. — Mucous  gland  :   submaxillary   of  dog 
resting  stage. 


INSALIVAT10N. 


175 


considers  them  to  be  undeveloped  mucous  cells,  destined  to  replace 
the  secreting  cells  when  they  shall  have  ceased  to  perform  their 
function  and  have  disappeared ;  while  other  opinions  are  that  they 
are  a  distinct  type  of  albuminous  cell,  or  are  due  to  a  post-mortem 
change.  Some  observers  claim  to  have  demonstrated  that  the 
lumen  of  the  albuminous  glands  is  continued  as  fine  capillary 
spaces  between  the  cells  of  these  glands,  and  that  from  these  pass 
off  smaller  branches  which  penetrate  the  cells  themselves,  and 
that  in  the  mucous  glands  these  same  capillaries  exist  only  in  con- 
nection with  the  demilunes.  If  this  is  confirmed,  it  would  seem 
to  be  more  than  probable  that  the  demilunes  have  distinct  secre- 
tory functions. 

The  albuminous  gland  secretes  a  watery  or  serous  fluid,  which 


FIG.  98.— Parotid  of  the  rabbit,  in  tbe  resting  condition  (after  Heidenhain). 

contains,  besides  water,  inorganic  salts,  some  albumin,  and  may 
also  contain  enzymes.  The  cells  of  this  variety  are  small  and 
compactly  fill  the  alveoli,  leaving  but  little  lumen  (Fig.  98). 
They  contain  albuminous  granules  which  are  very  distinct.  The 
parotid  gland  represents  the  serous  or  albuminous  type. 

The  human  submaxillary  gland  is  a  mixed  type  containing 
both  mucous  and  albuminous  alveoli,  the  latter,  however,  in  greater 
number. 

It  is  a  fact  that  in  mucous  glands  some  cells  are  found  which 
are  regarded  as  characteristic  of  the  albuminous  type,  and  vice 


176 


MOUTH  DIGESTION. 


versa;  so  that  it  has  been  suggested  that  it  would  be  better  to 
apply  the  terms  mucous  and  albuminous  to  the  cells,  rather  than 
to  the  glands. 

Secretory  Nerves  of  the  Salivary  Glands. — The  relation  existing 


D 

FIG.  99. — Parotid  gland  of  the  rabbit  in  a  fresh  state,  showing  portions  of  the 
secreting  tubules:  A,  in  a  resting  condition;  B,  after  secretion  caused  by  pilo- 
carpin  ;  C,  after  stronger  secretion — pilocarpin  and  stimulation  of  sympathetic  ;  D, 
after  long-continued  stimulation  of  sympathetic  (after  Langley). 

between  nerves  and  the  secretion  of  saliva  has  been  more  carefully 
investigated  in  dogs  and  rabbits  than  in  man,  and  it  is  to  the 
result  of  these  investigations  that  we  shall  especially  refer. 


Con  nee-  — . 
tive  tissue. 


Gland-cell    —  -, 
of  acinus. 


--  Intralobu- 
lar  duct. 


FIG.  100.— Section  from  parotid  gland  of  man  (Bohm  and  Davidoff). 

The  nervous  supply  of  the  parotid  gland  is  derived  from  :  (1) 
The  glossopharyngeal  nerve,  through  its  tympanic  branch  of  the 
nerve  of  Jacobson,  the  small  superficial  petrosal  nerve,  the  otic 


INSALIVATION.  177 

ganglion,  and  finally  the  auriculotemporal  branch  of  the  inferior 
maxillary  division  of  the  fifth  nerve  or  trigeminus.  This  is 
shown  in  Fig.  101.  (2)  The  cervical  sympathetic,  which  is  dis- 
tributed principally  to  the  walls  of  the  blood-vessels,  although 
some  of  its  fibers,  in  some  animals  at  least,  are  secretory. 

The  nervous  supply  of  the  submaxillary  and  sublingual  glands, 
like  that  of  the  parotid,  is  also  double,  the  chorda  tympani,  a 
branch  of  the  seventh  or  facial,  and  branches  of  the  sympathetic 
plexus  around  the  facial  artery,  being  the  nerves  supplying 
these  glands.  There  is  excellent  authority  for  the  statement 
that  the  chorda  tympani  is  in  reality  a  branch  of  the  glos- 
sopharyngeal  which  joins  the  facial  in  the  tympanum.  The 
chorda  tympani  joins  the  lingual  nerve  for  a  part  of  its  course, 
and .  then  leaves  it  to  pass  through  the  so-called  submaxillary 
ganglion  to  the  glands.  It  has  been  suggested  that  this  would  be 
more  properly  called  the  sublingual  ganglion,  inasmuch  as  only 
those  fibers  which  are  distributed  to  the  sublingual  gland  are  in 
communication  with  the  nerve-cells  of  this  ganglion,  while  those 
which  pass  to  the  submaxillary  gland  connect  with  a  collection  of 
nerve-cells  in  that  gland,  Langley's  ganglion.  The  course  of  the 
chorda  tympani  is  shown  in  Fig.  102. 

Effect  of  Stimulation  of  the  Chorda  Tympani  and  Sympathetic 
Nerves. — If  the  chorda  tympani  of  a  dog  is  stimulated  bv  passing 
through  it  weak  induction  shocks,  the  submaxillary  gland  secretes 
more  saliva.  The  small  arteries  of  the  gland  are  dilated  and  a 
larger  amount  of  blood  passes  through  the  gland,  giving  it  a  dis- 
tinctly reddish  appearance.  Stimulation  of  the  sympathetic  fibers 
produces  a  diminution  in  the  secretion,  and  the  reddish  color  dis- 
appears, leaving  the  gland  pale,  a  change  evidently  due  to  a  con- 
striction of  the  blood-vessels.  It  might  at  first  seem  that  the 
increase  in  the  amount  of  blood  caused  by  the  stimulation  of  the 
chorda  tympani  would  explain  the  increased  secretion  of  saliva  by 
filtration  of  the  fluid  of  the  blood  through  the  vessel-walls,  but 
experiments  have  shown  that  there  are  in  this  nerve  true  secretory 
fibers — i.  e.,  fibers  which  carry  impulses  to  the  secretory  structure 
of  the  gland,  and  that  the  cells  are  directly  stimulated  to  increased 
action.  We  may  briefly  refer  to  three  of  these  experiments  :  1. 
If  the  blood-supply  of  the  gland  is  cut  off,  and  the  chorda  tvm- 
pani  stimulated,  the  secretion  of  saliva  will  still  be  increased. 
2.  If  atropin  is  injected  into  the  animal  and  the  chorda  tympani 
then  stimulated,  the  blood-vessels  will  be  dilated,  but  there  will 
be  no  secretion.  3.  If  hydrochlorate  of  quinin  is  injected  into 
the  gland,  the  blood-vessels  dilate,  but  no  secretion  follows.  It 
will  be  seen  from  these  experiments  that  two  effects  are  produced 
by  stimulation  of  the  chorda  tympani  :  1.  A  dilatation  of  the 
blood-vessels ;  and  2.  A  direct  stimulation  of  the  cells.  From 
this  it  is  evident  that  there  are  two  sets  of  fibers  in  this  nerve, 
12 


178 


MOUTH  DIGESTION. 


each  having  a  distinct  function ;  one  vasodilator  and  the  other 
secretory.  There  are  also  two  sets  of  fibers  in  the  sympathetic 
nerves  which  supply  these  glands  :  One  vasoconstrictor — i.  e.,  when 


FIG.  101. — Schematic  representation  of  the  course  of  the  cerebral   fibers  to  the 

parotid  gland. 

stimulated  the  blood-vessels  are  constricted ;  and  the  other  secre- 
tory. It  is,  however,  mainly  through  the  chorda  tympani  that  the 
impulses  pass  which  cause  secretion. 


FIG.  102.— Schematic  representation  of  the  course  of  the  chorda  tympani  nerve  to 
the  submaxillary  gland. 

The  glossopharyngeal  fibers,  which  have  already  been  traced  to 
the  parotid  gland,  convey  the  impulses  which  cause  secretion  in 
this  gland.  The  sympathetic  nerves  are  vasoconstrictor  in  func- 
tion. 


1NSALIVATION. 


179 


FIG.  103. — A  number  of  alveoli  from 
the  submaxillary  gland  of  dog,  stained  in 
chrome-silver,  showing  some  of  the  fine 
intercellular  tubules  (Huber). 


From  the  mass  of  evidence  which  has  been  accumulated,  to 
only  a  small  part  of  which  have  we  made  reference,  it  is  indis- 
putably proved  that  there  are  true  secretory  fibers  distributed  to 
the  salivary  glands ;  and  the  same  is  true  of  other  glands  as  well, 
such  as  the  lachrymal,  perspiratory,  and  gastric  glands ;  but  the 
method  by  which  these  fibers  terminate  is  not  so  certain,  though 
it  appears  probable  that  it  is  by  forming  plexuses  between 
and  around  the  secreting 
cells.  Further  than  this,  it 
is  more  than  probable  that 
there  are  two  kinds  of  se- 
cretory fibers :  One  which 
transmits  impulses  that  cause 
the  secretion  of  the  organic 
constituents  of  the  saliva,  and 
called  trophic;  the  impulses 
conveyed  by  the  other,  the 
secretory  fibers  proper,  pro- 
ducing the  secretion  of  the 
water  and  the  inorganic  salts 
of  the  saliva. 

Paralytic  Secretion. — If 
the  chorda  tympani  is  cut, 
there  is  no  immediate  effect, 
but  after  a  day  or  two  the  gland  begins  to  secrete  a  very 
watery  saliva  which  continues  for  several  weeks,  and  then  it 
atrophies.  This  secretion  is  called  paralytic.  Although  the  sec- 
tion is  made  on  but  one  side,  both  glands  are  similarly  af- 
fected, and  the  secretion  on  the  opposite  side  to  the  section  is 
called  antiparalytic  or  antilytic.  There  are  two  explanations  given 
to  account  for  this  phenomenon.  One  is  that  the  continuous 
secretion  is  due  to  an  increased  irritability  of  the  secretion-center 
in  the  medulla  oblongata  and  of  the  nerve-cells  in  the  gland,  by 
which  the  venous  condition  of  the  blood  is  alone  sufficient  to  cause 
them  to  send  out  continuous  impulses  to  the  secreting  cells.  The  , 
other  theory  is  based  upon  the  fact  that  katabolic  changes  are 
going  on  in  the  cells  of  the  gland  which  are  inhibited  by  impulses 
coming  through  the  chorda  tympani ;  if,  therefore,  this  nerve  is 
cut,  such  impulses  no  longer  restrain  the  katabolic  changes,  and 
they  go  on  without  interference,  with  the  result  of  atrophy  of  the 
gland  and  the  formation  of  the  paralytic  secretion. 

Secretion  of  Saliva. — The  secretion  of  saliva  is  normally  a 
reflex  act.  It  is  ordinarily  brought  about  by  the  stimulation  of 
the  mucous  membrane  of  the  mouth  by  sapid  substances — that  is, 
those  which  excite  the  sense  of  taste,  although  chemical  and  even 
mechanical  stimuli  will  produce  the  same  result.  The  chewing 
of  a  piece  of  rubber  will  cause  a  profuse  flow  of  saliva.  The 


180  MOUTH  DIGESTION. 

glossopharyngeal  and  lingual  nerves  serve  as  the  afferent  nerves 
in  this  act,  carrying  the  impulses  to  a  center  in  the  medulla,  from 
which  efferent  impulses  pass  out  through  the  secretory  nerves  to 
the  glands.  This  center  may  be  stimulated  by  afferent  impulses 
reaching  it  through  other  nerves  ;  thus  salivary  secretion  may  be 
increased,  or  "  the  mouth  made  to  water,"  by  the  smell  or  even 
the  thought  of  food.  This  center  may  also  be  inhibited  from 
sending  out  secretory  impulses,  as  through  fright  or  other  nervous 
disturbance,  thus  diminishing  the  secretion  of  saliva  and  causing 
the  dry  mouth  and  throat  which  so  commonly  accompany  such 
conditions. 

Changes  in  the  Salivary  Cells.— Certain  changes  take  place  in 
the  salivary  cells  as  a  result  of  their  activity.  When  a  rabbit  is 
fasting,  the  cells  of  the  parotid  gland  are  granular  throughout, 
their  outlines  being  faintly  marked  by  light  lines.  If  it  is 
fed,  or  pilocarpin  injected,  or  the  sympathetic  stimulated,  the 
granules  disappear  from  the  outer  portion  of  the  cells,  so  that 
there  is  an  external  clear  border  surrounding  the  granular  in- 
terior. If  the  stimulation  continues,  the  granules  diminish  and 
are  collected  near  the  lumen  of  the  alveoli  and  at  the  margin 
of  the  cells,  the  clear  border  becomes  enlarged,  and  the  cells 
become  smaller.  The  explanation  of  this  is  that  the  granules 
contain  a  substance  which  is  or  which  becomes  the  ptyalin 
of  the  saliva.  If  it  should  be  demonstrated  hereafter  that 
there  is  a  zymogen  which  precedes  the  ptyalin,  it  would  receive 
the  name  of  ptyalinogen,  but  this  has  not  as  yet  been  proved  to 
occur.  These  granules  in  the  cells  are  called  zymogen  granules. 
While  these  granules  are  being  used  up  to  form  the  ptyalin  new 
material  is  being  deposited  by  the  blood  at  the  base  of  the  cells, 
which  in  turn  will  later  form  the  zymogen  or  ptyalin. 

Similar  changes  take  place  in  the  mucous  glands,  in  the  cells 
of  which  are  granules  (125  to  250  to  a  cell)  composed  of  mucin- 
ogen,  which  becomes  mucin,  and  is  in  this  form  discharged  into 
the  lumen  of  the  alveoli.  The  demilunes,  before  referred  to,  are 
situated  outside  these  cells  which  produce  the  mucinogen. 

Properties  and  Composition  of  the  Saliva. — The  secretion  of 
the  human  parotid  gland  is  a  clear  fluid,  though  sometimes  turbid, 
and  contains  some  epithelial  cells.  It  is  alkaline  in  reaction,  but 
less  so  than  the  saliva  of  the  submaxillary  gland.  Its  specific 
gravity  is  very  variable,  as  is  shoAvn  by  the  following  figures : 
Mitscherlich  gives  it  as  1.006  to  1.008  ;  Oehl,  1.010  to  1.012  with 
scanty,  and  1.0035  to  1.0039  with  plentiful  secretion  ;  Hoppe- 
Seyler,  1.0061  to  1.0088  ;  the  solids  being  from  5  to  16  parts  per 
1000.  It  contains  ptyalin  and  potassium  sulphocyanate,  but  no 
mucin. 

The  secretion  of  the  human  submaxillary  gland  is  clear  and 
watery,  always  alkaline,  and  has  a  specific  gravity  between  1.0026 


INSALIVATION.  181 

and  1.0033.  The  solids  are  from  3.6  to  4.6  parts  per  1000.  It 
contains  ptyalin,  but  authorities  differ  as  to  its  containing  potas- 
sium sulphocyanate. 

The  existence  of  such  ducts  as  those  of  Stenson  and  Wharton 
makes  it  easy  to  obtain  the  pure  secretions  of  the  parotid  and 
submaxillary  glands  by  the  introduction  into  them  of  caimulse ; 
but  this  is  not  true  of  the  sublingaal  gland,  hence  the  secretion  from 
this  gland  in  man  has  never  been  obtained  in  sufficient  quantity 
to  make  a  thorough  analysis  of  it,  but  it  is  known  to  be  more 
alkaline  than  that  of  the  submaxillary,  to  contain  mucin,  a  dias- 
tatic  enzyme,  and  potassium  sulphocyanate. 

The  secretion  of  the  mucous  glands  of  the  human  mouth  has 
never  been  obtained  pure,  or  in  quantity  sufficient  to  analyze.  It 
is  a  tenacious  and  viscid  secretion  and  alkaline  in  reaction. 

Mixed  saliva — i.  e.,  the  saliva  as  found  in  the  mouth — the 
product  of  all  the  salivary  glands,  is  a  clear  fluid,  viscid  in  con- 
sistency, with  a  specific  gravity  between  1.002  and  1.008,  alkaline 
in  reaction,  and  containing  from  5  to  10  parts  per  1000  of  total 
solids.  It  is  secreted  to  the  amount  of  between  300  and  1500 
grams  daily.  Moore  states  that  when  it  is  acid  this  reaction  is 
commonly  due  to  fermentation  of  particles  of  food  in  the  mouth. 
Many  authorities  state  that  it  contains  sodium  carbonate,  but 
Chittenden  and  Richards  make  the  following  statement :  "  Human 
mixed  saliva  contains  normally  no  sodium  carbonate  whatever ; 
the  alkalinity  indicated  by  litmus,  lacmoid,  etc.,  is  due  to  hy- 
drogen alkali  phosphates,  with  possibly  some  alkali  bicarbonate. 
Mixed  saliva  invariably  acts  acid  to  phenolphthalein. 

"  The  alkalinity  of  mixed  saliva,  as  indicated  by  lacmoid,  is 
greater  before  breakfast  than  after  the  morning  meal ;  a  conclusion 
which  stands  in  direct  opposition  to  the  statement  frequently  made 
that  '  the  alkalinity  (of  mixed  saliva)  is  least  when  fasting,  as  in 
the  morning  before  breakfast,  and  reaches  its  maximum  with  the 
height  of  secretion  during  or  immediately  after  eating.7  r' 

When  saliva  is  examined  under  the  microscope  there  are  seen 
epithelial  scales  from  the  mucous  membrane  of  the  mouth,  and 
leukocytes,  probably  from  the  tonsils  and  elsewhere,  described 
usually  as  salivary  corpuscles.  Bacteria  and  portions  of  food  are 
commonly  found  in  saliva,  but  they  are  not  constituent  parts,  but 
rather  impurities. 

Examined  chemically  the  saliva  is  found  to  contain  the  enzyme 
ptyalin,  mucin,  and  traces  of  proteid,  probably  of  the  nature  of  a 

flobulin,  but  too  little  in  amount  to  be  quantitatively  determined. 
t  contains  also,  though  not  invariably,  potassium  sulphocyanate, 
which  is  regarded  as  a  product  of  proteid  metabolism  ;  but  with 
our  present  knowledge  the  physiologic  value  of  this  constituent  is 
still  undetermined. 

The  inorganic  constituents  of  saliva  are  sodium  chlorid,  cal- 


182 


MOUTH  DIGESTION. 


ciura  phosphate  and  carbonate,  magnesium  phosphate,  and  potas- 
sium chlorid.  Although  it  is  commonly  stated  that  it  contains 
also  sodium  carbonate,  yet,  as  we  have  seen,  this  is  denied  by 
Chittenden  and  Richards,  whose  investigations  are  the  most  recent 
on  this  subject.  Calcium  carbonate  and  phosphate  occasionally 
form  salivary  calculi  in  the  glands  or  their  ducts,  and  may  require 
removal  by  the  surgeon.  These  salts  also  contribute  to  the  forma- 
tion of  the  tartar  on  the  teeth. 

The  following  table  gives  four  analyses  of  human  mixed  saliva, 
by  as  many  chemists.  It  should  be  remembered,  however,  that 
even  in  the  same  individual  the  composition  of  this  secretion 
varies  during  the  day,  and  that,  too,  independently  of  the  taking 
of  food.  Observation  has  shown  that  between  7  and  11  A.M., 
provided  no  food  is  taken,  its  composition  is  very  constant. 

Mixed  Human  Saliva. 


I. 

II. 

III. 

IV. 

Water 

992  9 

995  10 

994  10 

994  20 

Total  solids 

7  1 

4  84 

5  90 

5  80 

Suspended  solids  (epithelium,  mucus, 
etc  )          .    .                   .            . 

1.4 

1.62 

2.13 

2.20 

Soluble  organic  mutter  (ptyaliu  and 
albumin)      
Potassium  sulphocvanate     

3.8 

1.34 
0.00 

1.42 
0.10 

1.40 
0.04 

Inorganic  salts 

1  9 

1  82 

2  19 

2  20 

Office  of  Saliva. — This  is  twofold  :  (1)  chemical  and  (2)  mechan- 
ical. 

The  chemical  action  of  saliva  is  due  to  the  enzyme  ptyalin, 
which  is  undoubtedly  the  most  important  constituent  of  the 
mixed  saliva.  This  ingredient  exists  in  the  human  parotid  gland 
at  birth,  but  does  not  appear  in  the  submaxillary  gland  until  the 
age  of  two  months.  It  is  an  amylolytic  or  diastatic  enzyme — /.  <?., 
one  having  the  property  of  changing  starch  into  sugar.  Although 
it  resembles  diastase,  which  is  the  enzyme  obtained  from  malt,  in 
its  power  to  convert  starch,  still  the  enzymes  are  not  the  same. 
Thus,  the  optimum  temperature  for  ptyalin  is  46°  C.,  and  its  power 
is  destroyed  between  65°  C.  and  70°  C. ;  while  the  optimum 
temperature  for  diastase  is  between  50°  C.  and  56°  C.,  and  it  is 
destroyed  at  80°  C. 

Although  the  optimum  temperature  of  ptyalin  is  at  or  near 
46°  C.,  still  it  acts  vigorously  at  from  30°  C.  to  40°  C.  The  con- 
version of  starch  into  maltose  takes  place  as  follows  :  The  starch 
grains  being  acted  upon  by  hot  water,  take  it  up,  and  soluble 
starch  or  amylodextrin  is  produced.  The  action  of  ptyalin  upon 
this  is  to  convert  it  into  erythrodextrin  and  maltose  ;  the  ptyalin, 
continuing  its  hydrolytic  action,  changes  the  erythrodextrin  into 


INSALIVATION.  183 

achroodextrin  with  maltose,  and  the  dextrin  finally  becomes  mal- 
tose, so  that  in  the  end  all  the  starch  becomes  maltose.  It  is  con- 
sidered by  some  authorities  that  what  is  called  erythrodextrin 
consists  in  reality  of  several  dextrins,  and  this  is  undoubtedly 
true  of  achroodextrin,  of  which  maltodextrin  may  be  regarded  as 
a  variety.  Neumeister  gives  the  following  scheme  as  representing 
the  changes  through  which  he  believes  the  starch  passes : 

/  Maltose. 

Starch— soluble  starch  f 

(amylodextrin).  )  /Maltose. 


Erythrodextrin.  i  /Maltose 

Achroodextrin  a.  j  /Maltose. 

Achroodextrin  /3.  ^ 

/Maltose. 
Achroodextrin  y  j 
(maltodextrin).  "\ 

\Maltose. 

Glycogen,  when  acted  upon  by  ptyalin,  undergoes  the  same 
changes  as  starch,  but  less  rapidly.  Cellulose  is  not  affected  by  it, 
except,  possibly,  in  young  plants,  when  it  is  very  tender.  Inas- 
much as  the  external  portion  of  the  starch  grains  is  cellulose,  un- 
cooked starch  is  not  affected  by  this  enzyme.  This  is  one  of  the 
reasons  why  starchy  substances  should  be  cooked  before  being 
eaten.  In  the  cooking  process  the  starch  becomes  hydrated  by 
union  with  water,  and  upon  hydrated  starch  ptyalin  acts  more 
thoroughly. 

Effect-  of  Reaction  on  the  Amylolytic  Action  of  Saliva. — The 
saliva,  of  which  ptyalin  is  a  constituent,  is  an  alkaline  fluid,  and 
yet,  as  a  matter  of  fact,  this  enzyme  acts  at  its  best  when  the 
reaction  is  neutral.  If  the  alkalinity  is  excessive,  its  action  is 
inhibited.  When  free  hydrochloric  acid  is  present,  even  in  so 
small  an  amount  as  0.003  per  cent.,  the  amylolytic  action  is 
arrested,  and  if  much  more  than  this,  the  enzyme  is  destroyed. 

From  the  experiments  of  Chittenden  and  Richards,  to  which 
we  have  already  referred,  the  following  conclusions  are  drawn  by 
them  :  Saliva  secreted  after  a  period  of  glandular  inactivity  as 
before  breakfast,  manifests  greater  amylolytic  power  than  the 
secretion  obtained  after  eating.  This  increased  amylolysis  is  due 
primarily  to  an  increase  in  the  amount  of  active  enzyme  contained 
in  the  saliva.  Mixed  saliva,  whether  collected  by  mechanical 
stimulation  or  collected  without  effort,  shows  a  natural  tendency 
to  vary  in  amylolytic  power  throughout  the  twenty-four  hours,  and 
apparently  independently  of  the  taking  of  food.  This  is  remarkably 
constant  between  7  and  11  A.M.  Mechanical  stimulation,  as 
chewing  a  tasteless  substance,  and  alcohol,  ether,  gin,  whiskey,  etc., 
if  taken  into  the  mouth,  all  lead  to  the  outpouring  of  a  secretion 


184  MOUTH  DIGESTION. 

richer  in  alkaline-reacting  salts  and  in  amylolytic  power  than  the 
secretion  coming  without  stimulation.  Mixed  saliva  resulting 
from  stimulation  with  ether,  alcohol,  etc.,  contains  a  much  larger 
proportion  of  mucin  than  the  secretion  coming  without  stimula- 
tion, being  noticeably  thick  and  viscid.  This  quality  is  not  appar- 
ent in  the  saliva  resulting  from  mechanical  stimulation. 

Duration  of  the  Amylolytic  Action  of  Saliva. — One  of  the  in- 
teresting questions  in  regard  to  the  amylolytic  action  of  saliva  is 
as  to  its  duration.  As  we  have  already  seen,  a  very  minute  per- 
centage of  free  acid  arrests  this  action.  The  food  remains  in  the 
mouth  but  a  short  time,  when,  in  portions,  each  of  which  is  an 
alimentary  bolus,  it  passes  through  the  esophagus  into  the  stomach, 
a  process  which  is  also  very  brief,  and  in  the  latter  organ  it  meets 
with'  a  fluid,  the  gastric  juice. 

Although  the  amount  of  hydrochloric  acid  in  this  fluid  is 
enough  to  arrest  the  action  of  the  enzyme  if  it  was  free,  still  it 
must  not  be  forgotten  that  this  is  not  the  case.  It  is  in  combination 
with  the  proteids  of  the  gastric  juice,  and  later  with  the  proteids 
and  peptones  the  results  of  stomach  digestion,  so  that  consider- 
able time  must  elapse  before  there  is  enough  of  the  free  acid 
present  to  arrest  the  action  of  the  ptyalin.  Just  how  long  this 
is,  it  is  impossible  to  say  in  all  cases,  for  it  will  vary  under  different 
conditions.  Experiments  made  by  Cannon  (p.  201)  show  that 
while  the  contents  of  the  pyloric  end  of  the  stomach  are  strongly 
acid,  free  hydrochloric  acid  appearing  there  at  the  end  of  half  an 
hour,  at  the  end  of  two  hours  there  is  no  free  acid  in  the  middle 
of  the  food  in  the  cardiac  end,  so  that  during  all  this  time  the 
action  of  the  saliva  may  continue. 

In  discussing  this  subject  Moore  says :  "  The  diastatic  action 
of  the  saliva,  therefore,  continues  in  the  stomach  during  and  after 
a  meal  until  (1)  the  alkali  of  the  saliva  has  been  neutralized,  (2) 
the  proteid  present  in  solution  has  been  satisfied,  and  (3)  a  trace 
of  free  hydrochloric  acid  remains  in  excess." 

Some  excellent  authorities  are  inclined  to  regard  the  chemical 
action  of  the  saliva  as  subordinate  to  the  mechanical,  inasmuch  as 
in  their  opinion  the  amount  of  starch  converted  into  maltose  by 
the  ptyalin  is  inconsiderable.  This  they  infer  from  the  fact  that 
a  medium  as  acid  as  the  gastric  juice  will  inhibit  the  action  of  the 
enzyme,  and,  since  the  food  remains  in  the  mouth  and  esophagus 
but  a  short  time,  it  follows  that  the  conditions  favorable  for 
salivary  digestion  must  be  of  brief  duration.  It  seems  to  us  that 
they  ignore  the  facts,  already  stated,  with  reference  to  the  necessity 
of  free  acid  to  stop  the  action  of  the  enzyme,  and  to  the  long  time 
before  this  is  present  in  the  stomach  in  quantity  sufficient  to  pro- 
duce its  effect.  It  is  undoubtedly  true  that  the  starch  digestion 
of  the  small  intestine  is  very  important,  but  certainly  in  the  two 
hours,  approximately,  that  the  saliva  acts  a  considerable  amount 


INSALIVATION.  185 

of  starch  can  be  converted,  so  that  to  the  chemical  action  of  the 
saliva  must  be  assigned  a  greater  importance  than  it  has  hitherto 
held. 

Much  of  the  starch  not  changed  to  sugar  is  changed  to  dextrin, 
according  to  Cannon  and  Day,  "  and  thus,  since  dextrin  is  not  easily 
fermented,  the  food  is  saved  to  the  organism.  The  especial  value 
of  this  process  lies  in  the  fact  that  it  occurs  to  the  greatest  degree 
in  the  fundus,  in  which  region  the  hydrochloric  acid,  inhibiting  the 
action  of  many  of  the  organized  ferments,  does  not,  for  some  time, 
make  its  appearance. 

"  In  the  early  stages  of  gastric  digestion,  if  food  has  been  prop- 
erly masticated,  the  fundus  serves  chiefly  for  the  action  of  the 
ptyalin ;  the  pyloric  portion,  after  a  brief  stage  of  salivary  diges- 
tion, is  thereafter  the  seat  of  strictly  peptic  changes.  Later,  after 
two  hours  or  more,  as  the  contents  of  the  fundus  become  acid,  the 
food  in  the  stomach,  as  a  whole,  is  subjected  to  the  action  of  proteo- 
lytic  fermentation." 

The  experiments  of  Cannon  on  the  movements  of  the  stomach, 
to  which  we  shall  refer  in  detail  in  considering  the  function 
of  that  organ,  demonstrate  most  conclusively  that  in  the  process 
the  conditions  are  most  favorable  for  a  relatively  prolonged 
action  of  ptyalin  on  starch ;  the  principal  condition  being  the 
absence  of  movement  in  this  part  of  the  stomach,  so  that  die 
food  remains  here  in  an  alkaline  condition  for  a  considerable 
length  of  time.  This  action  of  the  saliva  for  so  long  a  time  after 
the  entrance  of  the  food  into  the  stomach  emphasizes  the  impor- 
tance of  thorough  mastication  and  insalivation. 

Mechanical  Office  of  Saliva. — While  the  teeth  are  thoroughly 
comminuting  the  food  they  are  at  the  same  time  working  saliva 
into  the  interstices  which  they  make  between  the  particles  of  the 
food.  This  process  not  only  facilitates  the  chemical  action  of  the 
ptyalin,  but  it  tends  also  to  keep  the  particles  separated,  so  that 
when  the  food  reaches  the  stomach  the  gastric  juice  may  the  more 
readily  permeate  it  and  produce  its  characteristic  action.  Saliva 
aids  also  in  softening  the  food,  thus  enabling  the  process  of  deglu- 
tition or  swallowing  more  easily  to  be  performed.  The  secretion 
of  the  mucous  glands  of  the  mouth  is  of  special  importance  in 
this  act,  the  mucus  secreted  being  of  a  ropy  consistency  and 
possessing  great  lubricating  properties.  Saliva  is  intimately  con- 
nected with  the  sense  of  taste.  Only  soluble  substances  are 
sapid — that  is,  excite  the  sense  of  taste.  Insoluble  substances 
have  no  taste.  It  is  for  this  reason,  among  others,  that  calomel 
is  such  an  excellent  cathartic  for  children ;  being  insoluble,  it  is 
tasteless,  and  they  readily  swallow  it.  Soluble  substances  not 
already  in  a  state  of  solution  are  dissolved  by  the  saliva,  and  in 
this  condition  excite  the  sense  of  taste.  When  in  a  febrile  or 
other  state,  in  which  the  secretion  of  the  saliva  is  greatly  dimin- 


186  MOUTH  DIGESTION. 

ished,  deglutition  is  difficult  and  the  sense  of  taste  is  markedly 
deteriorated. 

Deglutition. — This  is  the  act  of  swallowing,  and  for  purposes 
of  description  is  conveniently  divided  into  three  stages:  1.  From 
the  mouth  to  the  pharynx  ;  2.  Through  the  pharynx  to  the  esoph- 
agus ;  and  3.  Through  the  esophagus  to  the  stomach. 

First  Stage. — The  tongue  is  an  organ  composed  of  muscles, 
some  of  which  have  their  origin  outside  the  tongue  but  end  in  it, 
known  as  the  extrinsic  muscles,  and  others  which  are  situated 
wholly  within  the  organ,  and  constitute  its  greater  part ;  these  are 
the  intrinsic  muscles.  In  the  former  group  are  the  styloglossus, 
hyoglossus,  palatoglossus,  and  others ;  and  in  the  latter  the 
superior  lingualis  and  inferior  lingualis,  together  with  others  which 
we  need  not  name.  For  a  detailed  description  of  the  muscles  of 
the  tongue  the  reader  is  referred  to  anatomical  text-books.  The 
floor  of  the  mouth  is  made  up  of  the  two  mylohyoid  muscles, 
which  have  their  origin  in  the  mylohyoid  ridge  and  are  inserted 
into  the  hyoid  bone.  The  digastric,  stylohyoid,  and  geniohyoid 
muscles  need  also  to  be  mentioned  in  this  connection. 

After  the  solid  food  has  been  thoroughly  masticated  and  insali- 
vated, it  is  collected  by  the  tongue,  aided  by  the  cheeks,  and 
formed  into  a  small  mass,  the  alimentary  bolus.  This  is  placed 
upon  the  dorsum  of  the  tongue,  which  is  then  pressed  against  the 
roof  of  the  mouth  by  the  action  of  the  styloglossi  and  palatoglossi 
muscles,  thus  carrying  the  bolus  backward  to  the  base  of  the 
tongue.  There  is  also  contraction  of  the  anterior  belly  of  the 
digastric,  mylohyoid,  and  geniohyoid  muscles,  elevating  and 
moving  forward  the  hyoid  bone  and  the  tongue,  and  the  pharynx 
and  larynx  are  thus  carried  upward  and  under  the  bolus.  The 
bolus  is  now  at  the  anterior  pillars  of  the  fauces,  the  palato- 
glossi muscles  covered  with  mucous  membrane.  The  first  stage 
may  now  be  considered  to  end  and  the  second  begin.  Up  to  this 
point  the  movement  has  been  a  voluntary  one,  absolutely  under 
the  control  of  the  will,  for  it  would  be  possible  at  this  point  in 
the  process  to  eject  the  bolus  from  the  mouth.  It  is  probable, 
however,  that  under  ordinary  circumstances  the  latter  part  of  the 
first  stage  is  involuntary — i.  e.,  reflex — as,  indeed,  are  both  the 
second  and  the  third  stages  throughout. 

The  nerves  which  are  involved  in  the  first  stage  are  the  fifth 
nerve,  supplying  the  mucous  membrane  of  the  mouth  and  the  an- 
terior portion  of  the  tongue ;  and  the  glossopharyngeal,  which  is  dis- 
tributed to  the  posterior  third  of  that  organ.  These  are  the  sensory 
nerves,  or  those  which  carry  the  aiferent  impulses ;  the  motor 
nerves  are  the  hypoglossal,  supplying  the  muscles  of  the  tongue, 
the  mylohyoid  branch  of  the  inferior  dental,  the  largest  branch 
of  the  inferior  maxillary  branch  of  the  fifth,  which  supplies  the 
anterior  belly  of  the  digastric  and  the  mylohyoid. 


DEGLUTITION.  187 

Second  Stage. — In  this  stage  the  bolus  is  carried  through  the 
pharynx,  and,  simple  though  this  may  appear,  it  must  be  borne 
in  mind  that  there  are  other  openings  than  the  esophagus  which 
communicate  with  the  pharynx  into  which  the  bolus  might  be  car- 
ried ;  these  are  the  posterior  nares  and  the  larynx.  If  carried  into 
the  former,  no  danger  would  accrue  ;  but  if  into  the  latter,  and  it  was 
not  at  once  expelled  by  the  violent  act  of  coughing  which  it  would 
excite,  a  fatal  result  would  doubtless  ensue — either  immediately 
if  the  bolus  so  blocked  the  larynx  that  no  air  could  enter,  or  after  a 
longer  period  if  it  passed  through  and  brought  about  the  fatal 
result  by  setting  up  inflammation  of  the  air-passages  or  lungs. 

The  approximation  of  the  base  of  the  tongue  to  the  soft  palate 
and  the  contraction  of  the  anterior  pillars  of  the  fauces,  the  palato- 
glossi,  the  so-called  constrictors  of  the  isthmus  of  the  fauces,  shut 
off  the  pharynx  from  the  mouth  and  carry  the  bolus  backward  far 
enough  to  bring  it  within  the  influence  of  the  constrictors  of  the 
pharynx.  An  additional  obstacle  to  the  return  of  the  bolus  to 
the  mouth  is  the  elevation  and  carrying  backward  of  the  hyoid 
bone  by  the  contraction  of  the  posterior  belly  of  the  digastric  and 
the  stylohyoid  muscles.  Its  entrance  into  the  posterior  nares  is 
prevented  by  the  elevation  of  the  soft  palate  caused  by  the  action 
of  the  levator  palati,  which  is  innervated  by  the  facial,  according 
to  Kirkes,  or  the  internal  branch  of  the  spinal  accessory,  according 
to  Gray.  The  soft  palate  is  at  the  same  time  made  tense  by  the 
tensor  palati,  supplied  by  a  branch  from  the  otic  or  Arnold's 
ganglion  ;  by  the  contraction  of  the  palatopharyngei  muscles,  which 
form  the  posterior  pillars  of  the  fauces,  and  are  supplied  by  the  in- 
ternal branch  of  the  spinal  accessory ;  and  by  the  raising  of  the 
uvula,  due  to  contraction  of  the  azygos  uvulae.  The  contracted 
palatopharyngei  do  not  come  closely  together,  but  what  is  lacking 
in  their  approximation  is  made  up  by  the  uvula.  This  contraction 
of  the  palatopharyngei  also  raises  the  pharynx  and  thus  brings  the 
bolus  well  within  it.  It  will  be  readily  seen  that  the  changes 
just  described  not  only  result  in  shutting  off  any  possible  entrance 
to  the  posterior  nares,  but  also  form  of  the  soft  palate  and  the 
posterior  pillars  of  the  fauces,  with  the  uvula  between  them,  a 
continuous  surface  well  lubricated  with  mucus,  and  so  inclined 
as  to  direct  the  bolus  in  the  direction  which  it  should  take  to 
reach  the  esophagus. 

The  upper  portion  of  the  pharynx  is  in  reality  a  part  of  the 
respiratory  rather  than  the  alimentary  apparatus,  as  is  shown  by 
the  fact  that  its  mucous  membrane  is  covered  with  ciliated  epithe- 
lium, as  is  also  the  upper  surface  of  the  soft  palate. 

The  bolus  has  still,  however,  to  pass  the  opening  into  the 
larynx  without  gaining  entrance  thereto.  This  is  accomplished 
in  the  following  manner :  As  we  have  seen,  the  larynx  is 
raised  in  the  manner  described,  aided  by  the  thyrohyoid  muscle, 


188  MOUTH  DIGESTION. 

which  acts  to  raise  the  larynx  when  the  hyoid  bone  ascends,  and 
its  opening  closed  by  the  contraction  of  the  arytenoideus  and  the 
lateral  erico-arytenoidei,  supplied  by  the  inferior  or  recurrent 
laryngeal  nerve,  a  branch  of  the  pneumogastric. 

Whether  the  epiglottis  is  folded  back  or  remains  in  its  usual 
erect  position  during  deglutition  is  a,  matter  of  dispute.  Those 
who  claim  that  it  closes  the  glottis  give  various  arguments  to 
sustain  the  opinion  and  explain  how  it  takes  place.  The  action 
of  the  thyrohyoid,  just  referred  to,  is  regarded  by  one  authority  as 
causing  or  permitting  "  the  folding  back  of  the  epiglottis  over  the 
upper  orifice  of  the  larynx."  It  is  further  claimed  that  this 
movement  can  be  felt  by  simply  passing  the  finger  into  the  throat 
until  it  comes  in  contact  with  the  epiglottis  and  then  performing 
the  act  of  swallowing.  On  the  other  hand,  there  is  a  case  on 
record  in  which  enough  of  the  pharynx  was  removed  in  a 
surgical  operation  to  permit  the  actual  inspection  of  the  epiglottis 
during  the  act  of  swallowing,  and  it  was  observed  to  undergo  no 
change  of  position.  Whatever  may  be  the  fact  in  this  regard, 
there  is  no  question  that  the  larynx  is  perfectly  protected  against 
the  entrance  of  food,  even  though  the  epiglottis  does  not  fold 
back  during  the  act  of  deglutition. 

At  the  close  of  the  first  stage  the  pharynx  is  raised  so  as  to 
receive  the  bolus,  and  at  the  same  time  it  is  enlarged.  This  is 
due  to  the  forward  movement  of  the  larynx  and  the  tongue,  both 
of  which  as  they  are  elevated  are  also  carried  forward  ;  and  also 
to  the  contraction  of  the  stylopharyngei,  whose  action  is  to  draw 
upward  and  outward  the  sides  of  the  pharynx,  thus  separating 
them  and  enlarging  the  cavity  laterally.  The  bolus  being  well 
within  the  pharynx,  the  muscles  which  raised  the  latter  relax,  and 
it  descends,  carrying  with  it  the  bolus,  which  is  now  passed  along 
by  the  constrictors  of  the  pharynx  to  the  opening  of  the  esoph- 
agus. The  stylopharyngeus  receives  its  nerve-supply  from  the 
glossopharyngeal,  while  the  constrictors  are  supplied  by  the 
pharyngeal  plexus,  the  inferior  constrictor  being  supplied  by  the 
external  laryngeal  branch  of  the  superior  laryngeal  and  the  recur- 
rent laryngeal. 

Third  Stage. — In  this  stage  the  bolus  passes  through  the  esoph- 
agus into  the  stomach.  This  canal  is  about  23  cm.  in  length,  and 
from  1.8  to  2.4  cm.  in  breadth.  When  empty  its  wails  are  in 
apposition,  and  in  section  it  presents  the  appearance  of  a  trans- 
verse slit.  It  has  three  coats  :  1.  An  internal,  composed  of  mucous 
membrane,  covered  with  stratified  epithelium,  as  is  that  of  the 
mouth  and  that  of  the  pharynx  from  the  soft  palate  down.  2.  A 
submucous  coat,  in  which  are  the  esophageal  glands,  compound 
racemose  glands  which  open  by  ducts  upon  the  surface  of  the 
membrane,  and  which  secrete  mucus.  These  glands  are  most 
abundant  near  the  cardiac  orifice,  where  they  encircle  the  esoph- 


DEG  L  UTITION.  189 

agus.  3.  A  muscular  coat,  which  is  arranged  in  two  layers,  an 
inner  (circular)  and  an  outer  (longitudinal).  The  fibers  of  the 
circular  layer  form  at  the  cardiac  orifice,  where  the  esophagus 
enters  the  stomach,  a  sphincter  which  keeps  the  opening  closed, 
especially  when  the  stomach  contains  food.  The  muscular  tissue 
of  the  upper  third  is  principally  striated,  while  the  remainder  is 
of  the  involuntary  variety.  The  nerves  of  the  esophagus  come 
from  the  pneumogastric  and  the  sympathetic. 

The  circular  layer  of  the  muscular  coat  is  continuous  with  the 
inferior  constrictor,  and  the  contraction  of  the  fibers  of  this  layer 
follows  immediately  upon  that  of  the  constrictor,  carrying  the 
bolus  onward  in  its  passage  to  the  stomach.  This  is  a  continuation 
of  the  reflex  act  which  begins  certainly  in  the  pharynx,  possi- 
bly in  the  mouth.  The  bolus  stimulates  the  mucous  membrane 
as  it  passes  along,  and  a  wave  of  peristalsis  follows.  Thus  each 
successive  portion  of  the  muscular  coat  contracts  behind  the  bolus, 
gradually  pushing  it  onward.  When  it  reaches  the  cardiac  orifice, 
the  sphincter  relaxes  and  the  bolus  is  forced  into  the  stomach. 
This  can  sometimes  be  heard  by  applying  a  stethoscope  over  the 
epigastric  region.  The  time  occupied  by  the  passage  of  the  bolus 
from  the  beginning  of  swallowing  to  the  moment  it  enters  the 
stomach  is  about  six  seconds.  The  action  of  the  longitudinal  fibers 
is  not  understood,  although  some  authorities  think  that  their  con- 
traction precedes  that  of  the  circular  fibers,  and  thus  tends  to 
dilate  the  esophagus  and  bring  it  forward  over  the  bolus. 

The  process  of  deglutition  has  been  very  thoroughly  studied 
by  Falk  and  Kronecker,  by  Kronecker  and  Meltzer,  and  still 
more  recently  by  Cannon  and  Moser.  The  first-named  experi- 
menters have  shown  that  there  is  pressure  enough  produced  by 
the  rapid  contraction  of  the  muscles  of  the  mouth  to  force  liquid 
food  through  the  esophagus  independently  of  peristalsis,  and 
indeed  before  the  peristaltic  wave  passes  along.  Thus,  when  cold 
water  is  swallowed  its  presence  is  recognized  in  the  epigastrium 
almost  immediately ;  and  it  has  been  also  noted  by  them  that 
when  strong  acids  pass  through  the  esophagus  only  parts  of  it  are 
corroded,  and  not  the  entire  surface  of  the  mucous  membrane,  as 
would  be  the  case  were  they  swallowed  by  peristaltic  action. 

The  second  named  experimenters  conclude  from  their  experi- 
ments that  liquids  and  semisolids  are  forced  down  the  esophagus, 
or  "  squirted  "  down,  by  the  rapid  contraction  of  the  mylohyoid 
muscles,  nearly  as  far  as  the  cardia  (cardiac  orifice),  and  that  they 
remain  here  until  the  peristaltic  wave  reaches  this  point,  when 
they  are  carried  into  the  stomach,  which  is  about  six  or  seven 
seconds  from  the  beginning  of  swallowing. 

In  these  experiments  only  liquids  and  semisolids  were  employed, 
and  it  is  manifest  that  what  might  be  true  of  these  might  not  be 
true  of  solids.  It  was  to  determine  the  actual  movements  of 


190  MOUTH  DIGESTION. 

solids,  as  well  as  of  semisolids  and  liquids,  that  the  experiments 
of  Cannon  and  Moser  were  performed".  Some  of  these  were  on 
geese,  cats,  dogs,  and  horses,  and  some  on  man. 

The  following  is  the  "  summary  "  of  these  .later  experiments, 
as  published  in  the  American  Journal  of  Physiology : 

"  There  is  a  difference  in  swallowing  according  to  the  animal 
and  the  food  which  is  used. 

"  In  fowls  the  rate  is  slow  and  the  movement  always  peri- 
staltic, without  regard  to  consistency.  A  squirt-movement  with 
liquids  is  manifestly  impossible,  as  the  parts  forming  the  mouth 
are  too  hard  and  rigid.  With  this  diminution  of  propulsive 
power  in  the  mouth  there  is  observed  a  greater  reliance  on  the 
force  of  gravity.  The  head  is  raised  each  time  after  the  mouth 
is  filled,  and  the  fluid  by  its  own  weight  trickles  into  the  esoph- 
agus, through  which  it  is  carried  by  peristalsis. 

"  In  the  cat  the  movement  is  always  peristaltic  and  slightly 
faster  than  in  fowls.  A  bolus  takes  from  nine  to  twelve  seconds 
in  reaching  the  stomach.  Liquids  move  somewhat  more  rapidly 
than  semisolids  in  the  upper  esophagus.  In  the  lower  or  diaphrag- 
matic part  the  rate  is  very  much  slower  than  above,  and  is  the 
same  for  liquids  as  for  solids. 

"  In  the  dog  the  total  time  for  the  descent  of  the  bolus  is 
from  four  to  five  seconds.  The  food  is  always  propelled  rapidly 
in  the  upper  esophagus  and  moves  more  slowly  below.  This 
rapid  movement  is  frequently  continued  further  with  liquid  food. 
No  distinct  pause  was  observed  when  the  movement  of  the  bolus 
changed  from  the  rapid  to  the  slower  rate. 

"  In  man  and  the  horse  liquids  are  propelled  deep  into  the 
esophagus  at  a  rate  of  several  feet  a  second  by  the  rapid  con- 
traction of  the  mylohyoid  muscles.  Solids  and  semisolids  are 
slowly  carried  through  the  entire  esophagus  by  peristalsis  alone." 

The  peristalsis  of  the  esophagus  is  brought  about  by  afferent 
impulses  which  reach  the  center  of  deglutition  and  from  which 
efferent  impulses  pass  out  to  the  muscular  coat.  While  the  act 
is,  therefore,  principally  under  the  control  of  the  nervous  system, 
the  stimulation  of  the  successive  portions  of  the  mucous  membrane 
as  the  food  passes  along  may  have  some  part  in  its  production. 


STOMACH  DIGESTION. 


STOMACH  DIGESTION. 


191 


The  food  having  reached  the  stomach,  now  undergoes  stomach 

gastric  digestion. 

The  stomach  is  a  hollow  organ  into  which  the  esophagus  opens, 


FIG.  104. — Anterior  outlines  of  stomach.     His'  model. 

the  opening  being  called  the  cardia  or  cardiac  orifice,  and  which 
at  its  lower  end  communicates  with  the  small  intestine  through 
the  pyloric  orifice.  Its  greatest  diameter  is  from  24  to  26  cm., 
and  that  from  the  lesser  to  the  greater  curvature,  10  to  12  cm. 
It  can  hold  from  2.5  to  4  liters.  When  empty  its  walls  are  in 
apposition.  Its  form  and  position  are  shown  in  Figs.  104  and 
105. 

The  study  of  the  movements  of  the  stomach  by  Cannon  by  means 


FIG.  105.— Posterior  orftlines  of  stomach.    His'  model. 

of  the  Rontgen  ray,  using  subnitrate  of  bismuth  to  throw  a  dark 
shadow  on  the  fluorescent  screen  (p.  201),  has  brought  out  some 


192 


STOMACH  DIGESTION. 


facts  in  regard  to  the  anatomy  of  the  stomach  which  make  it  desir- 
able to  reproduce  here  the  outline  of  that  organ  as  demonstrated  by 

the  experiments  referred  to. 
Fig.  106  represents  the  stom- 
ach of  the  cat,  but  probably 
also  represents  in  all  im- 
portant particulars  the  hu- 
man stomach  as  well. 

Coats  of  the  Stomach. 
—  The  stomach  is  composed 
of  four  coats  :  Serous,  muscu- 
lar, submucous,  and  mucous. 
The  serous  coat  is  a  reflec- 
tion of  the  peritoneum.  The 
submucous  coat,  which  con- 
tains the  nerves  and  blood- 
vessels, is  of  special  interest 


FIG.  106. — The  cardiac  portion  is  all  that 
part  to  the  left,  as  the  stomach  lies  in  the 
body,  of  WX.  The  cardia  is  at  C.  The 
pylorus  is  at  P,  and  the  pyloric  portion  is 
the  part  between  P  and  WX.  This  has  two 
divisions  :  the  antrum,  between  P  and  YZ, 
and  the  pre-antral  part,  between  WX  and 
YZ.  The  lesser  curvature  is  on  the  top  of 
the  outline  between  C  and  P,  and  the 


greater  curvature  between  the  same  points      as  giving   to  the   milCOUS  COat 
along  the  lower  border   (Amer.  Journ.  of  t    m()biHtv    and 

Physiology). 


as   per- 


mitting it  to  form  folds, 
called  rugce,  when  the  cavity  is  empty.  This  structure  is  in 
striking  contrast  with  the  anatomic  structure  of  the  uterus,  in 
which  organ,  the  submucous  coat  being  absent  and  the  mucous 
lying  directly  upon  the  muscular  coat,  there  is  a  total  want 
of  mobility  of  the  membrane.  Aside  from  this  fact,  neither 
the  serous  nor  the  submucous  coat  has  any  special  physiologic 
interest.  The  muscular  coat  is  composed  of  three  layers :  lon- 
gitudinal, circular,  and  oblique.  The  longitudinal  layer  is  made 
up  of  fibers  continuous  with  similar  fibers  of  the  esophagus,  and 
is  most  external — that  is,  immediately  beneath  the  peritoneum. 
These  fibers  radiate  from  the  esophageal  or  cardiac  orifice,  and 
are  especially  abundant  in  the  region  of  the  greater  and  lesser 
curvatures.  They  extend  to  the  intestine,  where  they  form  a 
layer  of  the  muscular  coat  of  that  organ.  The  circular  layer  is 
situated  internal  to  the  longitudinal,  and,  as  the  name  implies,  its 
fibers  encircle  the  stomach — that  is,  are  in  general  at  right  angles 
to  the  longitudinal  axis  of  the  stomach.  At  the  pyloric  orifice  of 
the  stomach,  where  the  duodenum  begins,  these  circular  fibers  are 
aggregated  in  such  number  as  to  receive  the  name  of  pyloric 
muscle  or  sphincter  pyloricus.  Their  projection  into  the  interior 
of  the  organ  at  this  location  with  its  covering  of  mucous  mem- 
brane constitutes  the  pyloric  valve.  The  oblique  layer  is  found 
especially  at  the  cardiac  extremity  of  the  stomach. 

The  mucous  coat,  or  mucous  me'mbrane,  is  soft  and  velvety. 
Near  the  cardiac  orifice  the  membrane  is  about  1^-  mm.  in  thick- 
ness, and  near  the  pylorus  2  mm.,  while  in  general  between  these 
two  points  its  thickness  is  about  1  mm.  Its  surface  is  composed 


COATS  OF  THE  STOMACH. 


193 


of  columnar  epithelium,  which  secretes  the  mucus  found  in  the 
stomach  in  the  intervals  of  digestion,  this  mucus  being  a  con- 
stituent of  the  gastric  juice. 

In  the  mucous  membrane,  and  forming  a  part  of  it,  are  two 
sets  of  glands,  the  pylwic  glands,  so  called  from  their  abundance 
in  the  pyloric  portion  of  the  stomach,  and  the  cardiac  glands 
(Fig.  107),  which  are  so  called  because  of  their  occurrence  in  the 
cardiac  region.  The  pyloric  glands  were  formerly  called  mucous 
glands,  but  their  product  is  not  mucus ;  the  cells  are  of  the  serous 
type  described  in  connection  with  the  salivary  glands.  The  ducts 
of  both  cardiac  and  pyloric  glands  are  lined  by  columnar  epithe- 


FIG.  107.— Cardiac  glands.  Diagram  showing  the  relation  of  the  ultimate 
twigs  of  the  blood-vessels  ( V  and  A),  and  of  the  absorbent  radicals  (L)  to  the 
glands  of  the  stomach,  and  the  different  kinds  of  epithelium — namely,  above, 
cylindrical  cells  ;  small  pale  cells  in  the  lumen  ;  outside  which  are  the  dark  ovoid 
cells. 

lium  continuous  with  that  covering  the  mucous  membrane.  In 
the  tubes  of  the  pyloric  glands  are  granular  cells  called  chief  or 
central  cells.  The  same  kind  of  cells  are  found  in  the  tubes  of  the 
cardiac  glands  ;  and  beneath  these  cells — that  is,  between  them  and 
the  basement-membrane — are,  besides,  large*  cells,  which  are  ovoid 
in  shape,  the  parietal  or  oxyntic  cells.  These  cells  cause  the  base- 
ment-membrane against  which  they  lie  to  bulge  out.  The  chief 
cells  are  regarded  as  producing  the  pepsinogen  which  is  converted 
into  the  pepsin  of  the  gastric  juice,  and  the  parietal  cells  as  pro- 
ducing the  hydrochloric  acid,  although  the  latter  has  not  been 
certainly  demonstrated.  The  vascularity  of  the  stomach  is  very 
great.  In  the  intervals  of  digestion  the  mucous  membrane  is  of  a 

13 


194 


STOMACH  DIGESTION. 


FIG.  108.— Left  breast  and  side 
(erect  position),  showing  perforation 
of  the  walls  of  the  stomach  of  Alexis 
St.  Martin. 


pale  pinkish  color,  while  during  active  digestion  its  color  is  a  bright 
red.  This  change  in  color  is  due  to  the  greatly  increased  amount 
of  blood  present  in  the  blood-vessels  of  the  organ  at  this  time. 

The  pyloric  portion  is  specially  distinguished  by  the  name 
antrum  pylori,  and  is  that  part  situated  between  the  pyloric  orifice 
and  a  band  of  circular  fibers,  the  transverse  band  or  sphincter  aniri 
pylorici,  distant  from  the  orifice  about  10  cm.  In  modern 

physiology  this  portion  of  the 
stomach  is  invested  with  much 
interest,  and  is  referred  to  on  p. 
201. 

Prior  to  1822  the  process  of 
stomach  digestion  was  little  un- 
derstood. During  that  year 
Alexis  St.  Martin,  a  Canadian 
boatman,  eighteen  years  of  age, 
was  injured  by  the  accidental  dis- 
charge of  a  shot-gun,  the  muzzle 
of  which  was  not  more  than  two 
or  three  feet  from  him.  In  a 
"  Memorial "  to  the  Senate  and 
House  of  Representatives,  Dr. 
Beaumont,  an  American  surgeon, 

under  whose  care  the  patient  came,  says  :  "  The  wound  was  received 
just  under  the  left  breast,  and  was  supposed  at  the  time  to  be 
mortal.  A  large  portion  of  the  side  was  blown  off,  the  ribs  frac- 
tured, and  openings  made  into  the  cavities  of  the  chest  and  abdo- 
men, through  which  protruded  portions  of  the  lungs  and  stomach, 
much  lacerated  and  burnt.  .  .  .  The  diaphragm  was  lacerated  and 
a  perforation  made  directly  into  the  cavity  of  the  stomach,  through 
which  food  was  escaping  at  the  time  your  memorialist  was  called 
to  his  relief." 

When  the  wound  healed  there  remained  in  his  side  a  permanent 
opening  nearly  2J  cm.  in  diameter,  which  communicated  with  the 
cavity  of  the  stomach  (Fig.  108).  Dr.  Beaumont,  and  subsequently 
others,  carried  on  a  series  of  experiments  and  observations  extend- 
ing through  years,  and  the  present  knowledge  of  stomach  digestion 
is  largely  based  upon  this  remarkable  case. 

After  the  healing  of  his  wound  his  health  was  excellent,  and  he 
lived  to  be  eighty-three  years  of  age. 

During  the  intervals  of  digestion  the  mucous  membrane  of  the 
stomach  is  pale  in  color,  and  is  covered  with  a  transparent  and 
viscid  mucus  which  is  neutral  or  alkaline  in  reaction.  This 
mucus  is  the  product  of  the  epithelium  of  the  mucous  membrane. 
After  food  has  entered  the  stomach  drops  of  gastric  juice  appear 
at  the  mouths  of  the  glands. 

Quantity  of  Gastric  Juice. — The  amount  of  gastric  juice 


COMPOSITION  OF  HUMAN  GASTRIC  JUICE,  195 

daily  secreted  is  difficult  of  determination,  and  it  is  not  surprising 
that  authorities  should  differ  so  much  on  this  point.  Dr.  Beau- 
mont estimated  it  to  be  180  grams  in  the  case  of  St.  Martin,  while 
others  place  it  as  high  as  7  liters,  or  one-tenth  of  the  weight  of 
the  body.  The  gastric  juice  is  never  in  large  quantity  in  the 
stomach  at  any  one  time.  It  is  secreted  gradually  by  the  glands, 
is  poured  out  into  the  cavity  of  the  stomach,  where  it  permeates 
the  food,  is  passed  on  into  the  small  intestine,  where  it  is  absorbed 
by  the  blood-vessels,  and  is  then  returned  to  the  circulation,  from 
which  its  constituents  were  derived.  It  has  the  following  proper- 
ties :  it  is  clear,  nearly  colorless,  and  strongly  acid.  Its  specific 
gravity  is  about  1002. 

Composition  of  Human  Gastric  Juice  Mixed  with 
Saliva. — As  can  readily  be  understood,  it  is  impossible  to  obtain 
gastric  juice  unmixed  with  particles  of  food  or  saliva  or  other 
foreign  substances,  hence  an  accurate  analysis  cannot  be  given. 
The  analysis  by  Schmidt  of  gastric  juice  from  a  woman  having  a 
gastric  fistula,  which  is  the  only  complete  analysis  on  record,  is  as 
follows : 

Water 99.4400 

Organic  substances  (pepsin,  peptones,  and  rennin)     ...        .3195 

Free  hydrochloric  acid 0200 

Calcium  chlorid 0061 

Sodium        "  1464 

Potassium    " 0550 

Calcium        "| 

Magnesium  I  phosphates 0125 

Ferrum         J 

Loss .  _,    .        .0005 

100.0000 

The  constituents  of  the  gastric  juice  of  special  physiologic 
interest  are  hydrochloric  acid,  pepsin,  and  rennin.  It  was  at 
one  time  a  matter  of  dispute  whether  the  acidity  of  this  fluid  was 
due  to  hydrochloric  or  to  lactic  acid,  but  there  is  now  a  unanimity 
of  .opinion  that  it  is  the  former.  If  lactic  acid  is  present,  it  is 
probably  due  to  lactic  fermentation  which  has  taken  place  in  the 
carbohydrates  of  the  food  when  these  are  in  excess.  This  fermen- 
tation may  go  on  to  the  formation  of  acetic  and  butyric  acids, 
these  changes  being  doubtless  due  to  the  presence  of  micro- 
organisms. 

Hydrochloric  Acid. — The  amount  of  free  hydrochloric  acid  in 
human  gastric  juice  varies  from  0.05  to  0.3  per  cent.  Several  of 
the  best  authorities  give  the  average  as  between  0.2  and  0.3  per 
cent. 

Although  the  only  possible  source  of  hydrochloric  acid  is  the 
chlorids  of  the  blood,  which  decomposing  yield  chlorin,  and  this 
uniting  with  hydrogen  forms  the  acid,  yet  the  manner  of  its  for- 


196  STOMACH  DIGESTION. 

mation  is  still  undecided,  and  various  theories  have  been  pro- 
pounded to  explain  it.  Among  these,  Maly's  is,  perhaps,  the  one 
most  generally  accepted.  This  theory  is  that  there  occurs  a 
reaction  between  the  phosphates  and  chlorids  of  the  blood  which 
results  in  the  formation  of  hydrochloric  acid.  This  reaction  is 
expressed  by  the  following  equation  : 

NaH2P04     +     NaCl  Na2HPO4     +     HC1 

Sodium  dihydrogen  Sodium  Disodium  hydrogen       Hydrochloric 

phosphate.  chlorid.  phosphate.  acid. 

Or  the  hydrochloric  acid  may  be  produced  by  the  reaction  be- 
tween calcium  chlorid  and  disodium  hydrogen  phosphate,  as 
follows : 

3CaCl2  +    2Na2HPO4     —  Ca3  (PO4)2  +  4NaCl     -f    2HC1 

Calcium  Disodium  hydrogen       '    Calcium  Sodium  Hydrochloric 

chlorid.  phosphate.  phosphate.  chiorid.  acid. 

This  theory  regards  the  formation  of  the  hydrochloric  acid  as 
taking  place  in  the  blood ;  and  being  highly  diffusible,  it  diffuses 
through  the  gastric  glands  into  the  stomach.  In  this  explanation 
the  cells  have  no  part  in  the  formation  of  the  acid.  Gamgee  re- 
gards the  cells  of  the  glands,  those  known  as  parietal  or  oxyntic, 
as  the  acid  producers,  and  supposes  that  they  have  a  peculiar 
power  of  selecting  the  alkaline  phosphates  and  the  chlorids  from 
the  other  constituents  of  the  blood,  and  that  the  reaction  already 
referred  to  takes  place  in  them,  hydrochloric  acid  resulting.  But, 
as  we  have  already  said,  this  is  pure  theory,  and  has  never  been 
demonstrated.  About  all  that  can  be  said  is  that  the  hydrochloric 
acid  is  probably  produced  by  the  parietal  cells  from  the  chlorids 
of  the  blood,  and  that  is  their  special  function,  as  is  that  of  the 
chief  cells  to  produce  pepsinogen  or  the  cells  of  the  salivary 
glands  to  produce  ptyalin. 

Besides  the  action  of  hydrochloric  acid  in  connection  with 
digestion,  it  has  still  another  which  is  under  some  circumstances 
one  of  great  importance — that  is,  its  action  on  pathogenic  bacteria  ; 
we  shall  discuss  the  subject  of  Bacterial  Digestion  later  (p.  253), 
but  here  we  desire  to  call  attention  to  the  protective  influence 
which  the  hydrochloric  acid  of  the  gastric  juice  exerts  against 
certain  well-known  diseases. 

The  preservative  power  of  gastric  juice  on  meat,  due  to  the 
action  of  the  hydrochloric  acid  on  putrefactive  bacteria,  has  long 
been  known.  The  cholera  spirillum,  the  germ  which  produces 
Asiatic  cholera,  will  not  survive  in  fluid  of  the  acidity  of  the 
gastric  juice  of  the  guinea-pig  and  the  rabbit.  Nor  has  cholera 
been  produced  when,  after  first  neutralizing  the  gastric  juice 
by  administering  soda,  cholera  cultures  have  been  ingested.  But 
if  opium  is  given  with  the  soda,  and  intestinal  peristalsis  slowed 


COMPOSITION  OF  HUMAN  GASTRIC  JUICE.  197 

down  thereby,  choleraic  symptoms  result.  Koch  produced  genuine 
cholera  in  animals  by  opening  the  abdomen,  tying  the  bile-duct, 
and  then  injecting  cholera  cultures  directly  into  the  intestines. 
It  would  appear  from  the  evidence  taken  as  a  whole  that,  if 
the  stomach  is  in  a  normal  condition,  cholera  germs  will  be 
destroyed  by  the  gastric  juice.  It  is  not  improbable  that  if  the 
stomach  is  the  seat  of  catarrhal  inflammation,  as  might  be  caused 
by  alcohol  taken  for  a  long  time  in  excess,  the  conditions  in  the 
stomach-cavity  would  be  favorable  to  the  reception  and  growth 
of  the  cholera  spirilla,  and  the  disease  be  produced.  Falk  claims 
that  the  bacillus  of  anthrax  is  destroyed  by  gastric  juice,  except 
when  in  the  sporulating  stage,  but  that  this  fluid  has  no  effect  on 
the  tubercle  bacillus. 

Writing  on  this  general  subject,  Sternberg,  in  his  Manual  of 
Bacteriology,  says :  "  The  experiments  of  Straus  and  Wiirtz  and 
of  others  show  that  normal  gastric  juice  possesses  decided  germi- 
cidal  power,  which  is  due  to  the  hydrochloric  acid  contained  in  it. 
Hamburger  (1890)  found  that  gastric  juice  containing  free  acid  is 
almost  always  free  from  living  micro-organisms,  and  that  it 
quickly  kills  the  cholera  spirillum  and  the  typhoid  bacillus,  but 
has  no  effect  upon  anthrax  spores.  Straus  and  Wurtz  found  that 
the  cholera  spirillum  is  killed  by  two  hours7  exposure  in  gastric 
juice  obtained  from  dogs,  the  typhoid  bacillus  in  two  or  three 
hours,  the  anthrax  bacillus  in  fifteen  to  twenty  minutes,  and  the 
tubercle  bacillus  in  from  eighteen  to  thirty-six  hours.  The  ex- 
periments of  Kurlow  and  Wagner,  made  with  gastric  juice  ob- 
tained from  healthy  men  by  means  of  a  stomach-sound,  gave  the 
following  results :  Anthrax  bacilli  without  spores  failed  to  grow 
after  exposure  to  the  action  of  human  gastric  juice  for  half  an 
hour,  but  spores  were  not  destroyed  in  twenty-four  hours;  the 
typhoid  bacillus  was  killed  in  one  hour ;  the  cholera  spirillum,  the 
bacillus  of  glanders,  and  Bacillus  pyocyaneus  were  all  destroyed 
at  the  end  of  half  an  hour ;  the  pus  cocci  showed  great  resisting- 
power.  Certain  bacteria  have  a  greater  resisting-power  for  acids 
than  any  of  those  above  mentioned,  and  some  of  them  may  con- 
sequently pass  through  the  healthy  stomach  to  the  intestine  in  a 
living  condition,  but  there  is  good  reason  to  believe  that  the 
spirillum  of  cholera  or  the  bacillus  of  anthrax  would  not.  On  the 
other  hand,  the  tubercle  bacillus  and  the  spores  of  other  bacilli 
can,  no  doubt,  pass  through  the  stomach  to  the  intestine  without 
losing  their  vitality." 

The  hydrochloric  acid  of  the  gastric  juice  when  free  certainly 
destroys  many  non-pathogenic  bacteria  introduced  with  the  food, 
which  otherwise  might  cause  it  to  decompose ;  thus  both  lactic  and 
acetic  fermentations  are  prevented  ;  it  is  said,  however,  that  hydro- 
chloric acid  when  combined  with  proteids  does  not  have  this 
power.  Cohn  explains  the  action  of  the  free  acid  by  supposing 


198  STOMACH  DIGESTION. 

that  it  decomposes  the  alkaline  phosphates,  without  which  the 
bacteria  cannot  live. 

Pepsin — The  chief  or  central  cells  of  the  cardiac  glands  present 
a  granular  appearance  ;  this  is  due  to  granules  which  are  the  product 
of  the  cells,  and  consist  of  a  zymogen,  pepsinogen.  During  gastric 
digestion  they  diminish,  so  that  the  outer  portions  of  the  cells 
become  quite  clear,  losing  the  granular  appearance,  while  the 
inner  portions,  or  those  near  the  lumen  of  the  tube,  retain  it. 
While  the  chief  cells  of  the  cardiac  glands  doubtless  produce 
most  of  the  pepsinogen,  still  it  has  been  abundantly  proved 
that  the  same  variety  of  cells  of  the  pyloric  glands  also  produces 
this  zymogen.  The  pepsinogen  thus  formed  becomes  converted 
into  pepsin,  which  exists  in  the  human  stomach  at  birth. 

Pepsin  is  a  proteolytic  enzyme  which  acts  only  in  an  acid 
medium,  so  that  the  presence  of  the  acid  is  as  essential  to  stomach- 
digestion  as  is  that  of  the  enzyme.  While  hydrochloric  acid  gives 
the  best  results,  some  other  acids  may  be  substituted ;  thus  nitric 
and  lactic,  and  even  oxalic  and  tartaric  acids,  will  exert  a  pro- 
teolytic action. 

In  the  case  of  pepsin,  as  also  of  ptyalin,  and  indeed  of  all 
enzymes,  the  effect  of  temperature  upon  the  zymolytic  process 
must  always  be  considered.  The  optimum  temperature  for  the 
action  of  pepsin  is  from  37°  to  40°  C. ;  while  if  exposed  to  80°  C. 
in  a  moist  state,  the  enzyme  loses  its  proteolytic  power.  Low 
temperatures  inhibit  its  action,  but  it  still  acts,  though  feebly,  at 

o°c. 

It  has  already  been  stated  that  the  enzymes  have  not  as  yet 
been  obtained  in  sufficient  quantity  or  sufficiently  separated  from 
other  substances  to  analyze,  so  that  the  composition  of  pepsin  is 
still  undetermined. 

Pepsin-hydrochloric  Acid. — It  is  held  by  some  authorities  that 
the  pepsin  and  the  hydrochloric  acid  exist  in  gastric  juice  in 
a  state  of  combination,  to  which  the  name  of  pepsin-hydrochloric 
acid  has  been  given,  but  this  cannot  be  said  to  have  been  demon- 
strated. 

Rennin. — This  enzyme  exists  in  human  gastric  juice  at  birth, 
and  it  appears  to  be  more  abundantly  produced  in  the  fundus 
than  in  the  pyloric  region,  though  the  exact  seat  of  its  formation 
is  not  determined.  Its  action  is  to  coagulate  the  caseinogen ;  the 
changes  which  this  undergoes  in  the  process  of  coagulation  have 
already  been  fully  discussed  (p.  112),  and  need  not  be  repeated 
here.  Its  optimum  temperature  is  between  38°  and  40°  C.,  while 
at  63°  C.  in  an  acid  medium  it  is  destroyed.  The  curdling  proc- 
ess precedes  the  action  of  the  hydrochloric  acid  and  pepsin  during 
the  gastric  digestion  of  milk. 

Mothers  are  sometimes  alarmed  when  their  children,  seemingly 
in  perfect  health,  vomit  curdled  milk ;  but,  as  has  been  stated,  this 


ACTION  OF  THE  GASTRIC  JUICE.  199 

curdling  is  a  physiologic  process,  and  the  only  abnormality  is  its 
regurgitation,  which  is  usually  due  to  overfeeding. 

Action  of  the  Gastric  Juice. — Having  considered  the 
composition  of  the  gastric  juice,  we  are  now  in  a  position  to  dis- 
cuss its  action  upon  the  food. 

Action  on  Proteids. — When  proteids  reach  the  stomach  by 
the  process  of  deglutition  they  meet  with  the  gastric  juice,  whose 
hydrochloric  acid  converts  them  into  acid-albumins.  Some  writers 
use  the  term  syntonin  as  synonymous  with  acid-albumins ;  others 
restrict  its  use  to  the  special  acid-albumin  which  results  from  the 
action  of  the  acid  upon  myosin.  This  change  in  the  proteids  is 
more  quickly  and  completely  brought  about  by  the  acid  when 
pepsin  is  present  than  when  the  acid  acts  by  itself.  The  acid- 
albumin  (syntonin)  takes  up  water,  and  undergoes  a  "cleavage" 
or  splitting  up,  as  a  result  of  which  two  soluble  proteids  are 
formed,  proto-proteose  and  hetero-proteose,  which  are  together 
known  as  primary  proteases.  This  is  due  to  the  action  of  the 
pepsin,  which  is,  therefore,  a  proteolytic  enzyme.  The  process, 
however,  does  not  cease  here  ;  the  action  of  the  pepsin  continuing, 
the  primary  proteoses  take  up  water  and  in  turn  split,  forming 
secondary  or  deutero-proteoses.  These  in  turn  undergo  hydrolytic 
cleavage,  forming  as  final  products,  peptones.  Inasmuch  as  there 
are  doubtless  two  varieties  of  peptones,  as  will  be  seen  in  the  dis- 
cussion of  the  digestion  of  proteids  by  the  pancreatic  juice,  these 
are  called  ampho-peptones.  For  the  distinguishing  characteristics 
of  peptones  and  proteoses  the  reader  is  referred  to  p.  106. 

Action  on  Carbohydrates. — Cane-sugar  is  undoubtedly  inverted 
in  the  stomach  to  dextrose  and  levulose,  the  hydrochloric  acid 
being  the  agent  in  the  inversion.  All  the  cane-sugar  of  the 
food,  however,  does  not  undergo  this  change  in  the  stomach,  some 
of  it  not  being  inverted  until  it  reaches  the  small  intestine. 

There  is  some  evidence  looking  toward  the  presence  in  the 
gastric  juice  of  an  amylolytic  enzyme,  but  this  is  as  yet  too  incom- 
plete to  require  more  than  mention. 

The  changes  which  starch  undergoes  during  stomach  digestion 
are  elsewhere  described. 

Action  on  Fats. — The  temperature  of  the  stomach,  38°  C.,  ren- 
ders the  fats  more  fluid.  If  the  fat  is  in  the  form  of  adipose  tissue 
— that  is,  enclosed  in  adipose  vesicles — the  walls  of  the  latter  being 
proteid  in  character  undergo  proteid  digestion,  setting  the  fat  free ; 
but  the  latter  is  not  emulsified.  The  evidence  that  fat  is  split  up 
and  fatty  acids  liberated  in  the  stomach  is  accumulating ;  it  is 
believed  that  this  is  due  to  a  lipolytic  enzyme,  whose  action  is  in- 
hibited by  hydrochloric  acid  and  pepsin. 

Action  on  Albuminoids. — Of  all  the  albuminoids  which  enter 
into  the  food,  gelatin  is  the  most  important.  It  is  found  in 


200  STOMACH  DIGESTION. 

various  jellies  and  in  soups.  When  acted  upon  by  hydrochloric 
acid  and  pepsin  it  becomes  converted  into  gelatoses.  In  the  stom- 
ach these  undergo  no  further  change,  but  in  the  intestine  gelatoses 
become  gelatin  peptones  under  the  influence  of  the  trypsin  of  the 
pancreatic  juice. 

Movements  of  the  Stomach. — These  were  observed  very 
carefully  by  Dr.  Beaumont  in  the  case  of  St.  Martin  (p.  194),  and 
in  order  that  we  may  the  better  refer  to  the  results  of  recent 
investigations  we  will  here  quote  his  description.  He  says : 
"  The  bolus,  as  it  enters  the  cardia,  turns  to  the  left,  passes  the 
aperture,  descends  into  the  splenic  extremity,  and  follows  the 
great  curvature  toward  the  pyloric  end.  It  then  returns  in  the 
course  of  the  small  curvature,  makes  its  appearance  again  at  the 
aperture,  in  its  descent  into  the  great  curvature,  to  perform  similar 
revolutions."  This  occupied  in  St.  Martin's  case  from  one  to 
three  minutes. 

Before  describing  the  results  of  Cannon's  experiments  as 
recorded  in  the  American  Journal  of  Physiology,  and  which  were 
performed  upon  cats,  we  will  first  describe  the  movements  of  the 
human  stomach,  as  they  are  usually  described. 

Before  food  enters  the  stomach,  this  organ  being  empty,  its 
walls  are  in  apposition  and  its  mucous  membrane  arranged  in  rugae. 
The  first  portions  of  food  that  enter  separate  the  walls,  but  in  all 
portions  except  where  the  food  is  they  are  still  in  contact.  The 
presence  of  food  stimulates  the  muscular  coat,  and  as  a  result  the 
circular  fibers  begin  to  contract  feebly  and  on  the  side  of  the  great 
curvature,  setting  up  a  wave  of  peristalsis  which  travels  on  toward 
the  pylorus,  becoming  stronger  as  it  progresses.  Just  before  it 
reaches  the  antrum  it  appears  to  be  stopped  by  the  "  pre-antral  " 
constriction,  which  is  the  name  given  by  Hofmeister  and  Schlitz, 
to  whom  we  owe  these  observations,  to  a  constriction  of  circular 
fibers  which  surrounds  the  whole  stomach  in  this  region.  This  has 
the  effect  of  pushing  some  of  the  stomach-contents  into  the 
antrum ;  the  sphincter  antri  pylorici  now  contracts,  and  the 
antrum  is  practically  shut  off  from  the  fundus.  The  muscular 
coat  of  the  antrum  then  contracts,  and  its  contents  are  forced 
against  the  pylorus.  The  pyloric  muscle  relaxes  to  permit  liquid 
material  to  pass  through  into  the  duodenum  ;  if,  however,  solid 
particles  come  against  it,  the  relaxation  does  not  occur,  but  an 
antiperistaltic  wave  is  set  up  in  the  musculature  of  the  antrum 
which  carries  the  materials  back  into  the  fundus,  the  separation 
of  the  latter  from  the  antrum  having  ceased  owing  to  the  relaxa- 
tion of  the  sphincter  antri  pylorici.  The  contents  are  thus  re- 
tained in  the  stomach  to  be  further  acted  upon  by  the  gastric 
juice  until  they  are  rendered  sufficiently  liquid  to  pass  the  pylorus. 
During  these  muscular  movements  the  food  is  not  only  carried 


MOVEMENTS  OF  THE  STOMACH.  201 

toward  the  pylorus,  but  it  is  also  thoroughly  mixed  with  the 
gastric  juice,  and  thus  the  action  of  the  latter  is  more  compltee 
and  efficient  than  it  otherwise  would  be. 

Experiments  of  Cannon. — We  deem  a  somewhat  detailed  account 
of  these  experiments  warranted,  for  the  reason  that,  although 
they  were  made  upon  the  cat,  the  evidence  is  conclusive  that  the 
character  of  the  movements  of  the  human  stomach  during  diges- 
tion differs  in  no  essential  particular  from  that  of  the  movements 
of  the  stomach  of  the  animal  which  was  the  subject  of  experi- 
mentation. 

Cannon  and  Day  state  that  "  observations  with  the  x-rays  have 
proved  that  the  stomach  of  the  cat  is  like  that  of  the  dog,  rat,  rab- 
bit, guinea-pig,  and  man,  in  being  separable  into  two  parts  :  the 
quiet  cardiac  end  and  the  active  pyloric  end.  Moreover,  the  mucosa 
of  the  cat's  stomach  resembles  that  of  the  dog  and  of  man,  not 
only  in  structure  but  also  in  pouring  out  an  active  secretion  from 
almost  every  part  of  its  surface." 

Movements  of  the  Pyloric  Part. — Within  five  minutes  after  a 
cat  has  finished  a  meal  of  bread  mixed  with  subnitrate  of  bismuth 
there  is  visible  near  the  duodenal  end  of  the  antrum  a  slight 
annular  contraction  which  moves  peristaltically  to  the  pylorus ; 
this  is  followed  by  several  waves  recurring  at  regular  intervals. 
Two  or  three  minutes  after  the  first  movement  is  seen,  very 
slight  constrictions  appear  near  the  middle  of  the  stomach,  and, 
pressing  more  deeply  into  the  greater  curvature,  course  slowly 
toward  the  pyloric  end.  As  new  regions  enter  into  constriction 
the  fibers  just  previously  contracted  become  relaxed,  so  that 
there  is  a  true  moving  wave,  with  a  trough  between  two  crests. 
When  a  wave  swings  round  the  bend  in  the  pyloric  part  the 
indentation  made  by  it  deepens,  and  as  digestion  goes  on  the 
antrum  elongates  and  the  constrictions  running  over  it  grow 
stronger,  but,  until  the  stomach  is  nearly  empty,  do  not  divide  the 
cavity.  After  the  antrum  has  lengthened,  a  wave  takes  about 
thirty-six  seconds  to  move  from  the  middle  of  the  stomach  to  the 
pylorus.  At  all  periods  of  digestion  the  waves  recur  at  intervals 
of  almost  exactly  ten  seconds.  It  results  from  this  rhythm  that 
when  one  wave  is  just  beginning  several  others  are  already  run- 
ning in  order  before  it.  Between  the  rings  of  constriction  the 
stomach  is  bulged  out  (Figs.  109-111).  In  one  experiment  the 
cat  was  fed  15  grams  of  bread  at  10.25  A.M.  The  waves  were 
running  regularly  at  11  o'clock.  The  stomach  was  not  free 
from  food  until  6.12  P.M.  At  the  rate  of  360  waves  per  hour, 
approximately  2600  waves  passed  over  the  antrum  during  the 
single  digestive  period. 

Movements  of  the  Pyloric  Sphincter. — Ten  or  fifteen  minutes 
elapse  after  the  first  constriction  of  the  antrum  before  food  appears 


202 


STOMACH  DIGESTION. 


FIG.  109.  FlGt  m 

(Cannon,  in  American  Journal  of  Physiology.} 


MOVEMENTS  OF  THE  STOMACH. 


203 


FIG.  111.— Figs.  109, 110,  and  111 
present  outlines  of  the  shadow  of 
the  contents  of  the  stomach  cast  on 
a  fluorescent  screen  by  the  Rontgen 
rays.  The  drawings  were  made  by 
tracing  the  outline  of  the  shadow 
on  tissue-paper  laid  upon  the  fluor- 
escent surface,  and  are  about  one- 
half  the  actual  size.  They  show 
the  change  in  the  appearance  of 
the  stomach  at  intervals  of  half  an 
hour  from  the  time  of  eating  until 
the  stomach  is  nearly  empty  (Am. 
Jour,  of  Physiology}. 

and   that  the   constrictions 


in  the  duodenum.  This  is  spurted 
through  the  pylorus  and  shoots  along 
the  intestine  for  two  or  three  centi- 
meters. Not  every  constriction-wave 
forces  food  from  the  antrum.  In  one 
of  the  experiments  which  were  con- 
ducted by  Cannon,  about  an  hour 
after  the  movements  began,  three 
consecutive  waves  squirted  food 
into  the  duodenum.  The  pylorus 
remained  closed  against  the  next 
eight  waves,  opened  for  the  ninth, 
but  closed  again  for  the  tenth  and 
eleventh.  In  this  irregular  manner 
the  food  passed  from  the  stomach. 
Cannon  expresses  the  opinion  that 
near  the  end  of  gastric  digestion, 
when  the  constrictions  are  very 
deep,  the  pylorus  may  open  for 
every  wave.  When  a  hard  bit  of 
food  reaches  the  pylorus,  the 
sphincter  closes  tightly  and  re- 
mains closed  longer  than  when  the 
food  is  soft.  On  one  occasion,  dur- 
ing these  experiments,  when  a  hard 
particle  of  food  reached  the  pylorus, 
the  sphincter  opened  only  seven 
times  in  twenty  minutes.  It  is 
inferred  from  these  results  that  hard 
morsels  keep  the  pylorus  closed  and 
hinder  the  passage  of  the  food  into 
the  duodenum. 

Activity  of  the  Cardiac  Portion. — 
The  part  played  by  the  cardiac  por- 
tion has  not  hitherto  been  properly 
appreciated.  It  has  been  regarded 
as  the  place  for  peptic  digestion  or 
as  a  passive  reservoir  for  food  ;  but 
it  is  in  fact  a  most  interestingly  ac- 
tive reservoir.  Figs.  109-111  rep- 
resent the  appearances  the  stomach 
presents  at  various  stages  in  a  diges- 
tive period.  A  comparison  of  them 
shows  that  as  digestion  proceeds  the 
antrum  appears  gradually  to  elon- 
gate and  acquire  a  greater  capacity, 
make  deeper  indentations  in  it;  but 


204  STOMACH  DIGESTION. 

when  the  fundus  has  lost  most  of  its  contents  the  longitudinal  fibers 
of  the  antrum  contract  to  make  it  shorter  and  smaller. 

The  first  region  to  decrease  markedly  is  the  pre-antral  part  of 
the  pyloric  portion.  The  peristaltic  undulations,  caused  by  the 
circular  fibers,  start  at  the  beginning  of  this  portion  and  gradually, 
by  their  rhythmic  recurrence,  push  some  of  the  contents  into  the 
antrum.  As  the  process  continues  the  smooth  muscle-fibers  with 
their  remarkable  tonicity  contract  closely  about  the  food  that 
remains,  so  that  the  middle  region  comes  to  have  the  shape  of  a 
tube  (Figs.  110,  111,  1.30  P.M.  to  5.30  P.M.),  with  the  rounded 
fundus  at  one  end  and  the  active  antrum  at  the  other.  Along 
the  tube  very  shallow  constrictions  may  be  seen  following  one 
another  to  the  pylorus. 

At  this  juncture  the  longitudinal  fibers  which  cover  the  fundus 
like  radiating  fingers,  and  the  circular  and  oblique  fibers  reaching 
in  all  directions  about  this  spherical  region,  begin  to  contract. 
Thus  the  contents  of  the  fundus  are  squeezed  into  the  tubular 
portion.  This  process,  accompanied  by  a  slight  shortening  of  the 
tube,  goes  on  until  the  shadow  cast  by  the  fundus  is  almost  obliter- 
ated (Fig.  Ill,  5.30  P.M.).  This  shows  that  the  fundus  is  nearly 
empty,  for  there  being  but  little  subnitrate  of  bismuth  in  it,  only 
a  small  shadow  is  cast. 

The  waves  of  constriction  moving  along  the  tubular  portion 
force  the  food  onward  as  fast  as  they  receive  it  from  the  contract- 
ing fundus,  and  when  the  fundus  is  at  last  emptied  they  sweep  the 
contents  of  the  tube  into  the  antrum  (Fig.  Ill,  5  P.M.  to  6  P.M.). 
Here  the  operation  is  continued  by  the  deeper  constrictions,  till 
finally  (in  this  instance,  at  6.12  P.M.),  with  the  exception  of  a 
slight  trace  of  food  in  the  fundus,  nothing  at  all  is  to  be  seen  in 
the  stomach. 

The  food  in  the  fundus  may  possibly  be  slightly  affected  by 
the  to-and-fro  movements  of  the  diaphragm  in  respiration.  With 
normal  breathing  the  upper  border  of  the  cardiac  portion  swings 
through  about  one  centimeter ;  with  dyspnea,  or  deep  breathing, 
through  one  and  a  half  or  two  centimeters.  Since  the  lower 
border  does  not  move  so  much,  the  contents  are  gently  pressed, 
and  then  released  from  pressure,  at  each  respiration. 

Cannon  calls  attention  to  the  observation  made  by  Moritz  with 
reference  to  the  value  of  an  organ  like  the  stomach  for  holding 
the  bulk  of  the  food,  and  serving  it  out  little  at  a  time  so  that  the 
intestines  may  not  become  congested  during  their  digestive  and 
absorptive  processes,  and  says  that  all  of  the  advantages  supposed 
to  be  thus  secured  to  the  intestines  may  tie  claimed  for  the  stomach 
itself. 

The  experiments  above  quoted  prove  that  the  stomach  is  com- 
posed of  two  physiologically  distinct  portions.  The  busy  antrum, 
over  which  during  digestion  constriction-waves  are  running  in 


VOMITING.  205 

continuous  rhythm ;  and  the  cardiac  part,  which  is  an  active  reser- 
voir, pressing  out  its  contents  a  little  at  a  time  as  the  antral 
mechanism  is  ready  to  receive -them. 

Effect  of  the  Movements  of  the  Stomach  upon  the  Food. — The 
experiments  of  Cannon  demonstrate,  in  the  cat  at  least,  that  the 
idea  of  Beaumont  that  there  is  what  may  be  called  a  circulation 
of  food  from  the  cardia  along  the  greater  curvature  to  the  pylorus, 
and  back  along  the  lesser  curvature,  and  that  of  Brinton  that  there 
are  peripheral  currents  from  the  cardia  along  the  walls  of  the 
stomach  to  the  pylorus,  and  that  these  currents  then  unite  and 
come  back  to  the  cardia  as  an  axial  current,  are  incorrect.  What 
has  been  actually  observed  by  Cannon  shows  conclusively  that  as 
the  constriction-waves  approach  a  given  portion  of  food,  this  latter 
is  pushed  forward  in  the  direction  of  the  pylorus,  but  not  moving 
as  fast  as  the  wave,  the  constriction  overtakes  it,  and  as  it  passes 
it  pushes  the  food  backward,  for  in  this  direction  is  the  least 
resistance ;  the  next  wave  pushes  it  forward  a  little  further  than 
the  preceding  one,  and  as  it  passes  again  it  is  pushed  backward, 
but  all  the  time  it  is  making  headway,  though  slowly,  for  the 
progress  exceeds  the  backward  movement.  This  to-and-fro  move- 
ment is  more  marked  in  the  antrum,  where  the  waves  are  deep, 
than  in  the  middle  region. 

On  different  occasions  the  portions  of  the  food  under  observa- 
tion have  occupied  from  nine  to  twelve  minutes  in  passing  from 
where  the  waves  first  affected  them  to  the  pylorus — i.  e.,  on  the 
way  they  were  moved  back  and  forth  by  more  than  fifty  con- 
strictions. 

When  the  pylorus  is  closed,  the  food  being  pushed  forward  by 
the  advancing  constrictions,  which  are  here  very  deep,  and  not 
being  able  to  escape  into  the  duodenum,  is  squirted  back  through 
the  constricted  ring.  This  process  is  repeated  again  and  again 
until  the  sphincter  relaxes  and  the  fluid  parts  pass  out,  or  if  not 
rendered  liquid  pass  into  the  duodenum  later  in  a  solid  condition. 
The  solid  portions  then  remain  in  the  antrum,  to  be  here  acted 
upon  by  the  gastric  juice,  and  to  be  subjected  to  the  tireless  rubbing 
of  the  muscular  coat. 

In  the  above  resume  we  have  used  the  language  of  the  experi- 
menter in  describing  his  observations,  condensing  it  where  possi- 
ble, but  endeavoring  not  to  alter  his  interpretation  of  the  experiments. 

The  researches  of  Pawlow  lead  to  the  conclusion  that  the  relax- 
ation of  the  sphincter  pylori  is  due  to  the  contact  of  free  hydro- 
chloric acid,  and  not  to  any  mechanical  action  of  the  food. 

Vomiting". — The  act  of  vomiting  consists  in  an  expulsion  of 
the  contents  of  the  stomach  through  the  esophagus  and  the  mouth. 
Before  the  expulsive  act  takes  place  there  are  commonly  nausea 
and  an  increased  secretion  of  saliva.  Then  a  deep  inspiration 
occurs,  caused  by  the  descent  of  the  diaphragm  ;  the  glottis  is 
closed  by  the  contraction  of  the  arytenoid  and  the  lateral  crico- 


206  STOMACH  DIGESTION. 

arytenoid  muscles ;  and  the  posterior  nares  are  closed  by  the  con- 
traction of  the  palatopharyngei  muscles  or  the  posterior  pillars  of 
the  fauces.  The  cardiac  sphincter  becoming  relaxed,  the  cardia 
opens ;  while  the  pyloric  sphincter  being  contracted,  the  pyloric 
orifice  is  closed.  The  abdominal  muscles  now  contract,  and  the 
diaphragm  forming  a  non-yielding  wall  above  the  stomach,  this 
organ  is  so  compressed  that  its  contents  are  forced  into  the  esoph- 
agus with  sufficient  power  to  carry  them  through  the  mouth  to 
the  exterior.  Under  some  circumstances  this  force  is  sufficient  to 
eject  them  into  the  posterior  nares  and  out  through  the  nose. 

Although  the  abdominal  muscles  are  the  principal  factors  in 
producing  the  expulsive  movements,  and  indeed  are  in  themselves 
sufficient,  as  was  demonstrated  by  Magendie  when  he  removed  the 
stomach  and  substituted  for  it  a  bladder  containing  water,  still 
there  is  also  a  contributing  factor  in  the  antiperistaltic  contraction 
of  the  muscular  coat  of  the  stomach.  Under  some  circumstances 
there  is  also  an  antiperistaltic  wave  in  the  muscular  coat  of  the 
small  intestine,  by  which  its  contents  are  forced  into  the  stomach 
and  then  vomited.  Whether  this  antiperistaltic  action  occurs  or 
not  in  the  muscular  coat  of  the  esophagus  is  a  matter  which  is 
still  unsettled. 

The  above  description,  which  fairly  represents  the  modern  views 
as  to  the  act  of  vomiting,  is  modified  by  the  investigations  of  Open- 
chonski  on  dogs  and  rabbits,  and  still  more  recently  by  Cannon  on 
cats.  The  former's  description  is  as  follows  :  "  As  the  result  of 
an  emetic  there  occurs  a  quickening  of  the  walls  of  the  stomach 
near  the  pylorus,  which  appears  later  in  the  antral  and  middle 
regions  of  the  stomach.  This  becomes  a  contraction  most  marked 
in  the  antrum.  The  fundus  enlarges  in  a  spherical  form,  and  into 
it  the  contents  of  the  stomach  are  forced  by  these  contractions  of 
the  antrum  ;  then  follow  the  contractions -of  the  abdominal  muscles 
which  force  the  contents  into  the  esophagus." 

Cannon  made  his  observations  upon  a  cat,  to  which  he  gave 
apomorphin  as  an  emetic.  The  upper  circular  muscles  relax  and 
become  so  flaccid  that  the  slightest  movement  of  the  abdomen 
changes  the  form  of  the  fundus.  Then  there  are  apparently 
irregular  twitchings  of  the  fundus  wall.  Soon  a  deep  constriction 
starts  about  three  centimeters  below  the  cardia,  and,  growing  in 
strength,  moves  toward  the  pylorus.  When  it  reaches  the  trans^ 
verse  band  the  constriction  tightens  and  holds  fast,  while  a  wave 
of  contraction  sweeps  over  the  antrum.  Another  similar  constric- 
tion follows.  In  the  interval  the  transverse  band  relaxes  slightly, 
but  tightens  again  when  the  second  wave  reaches  it.  Perhaps  a 
dozen  such  waves  pass ;  then  a  firm  contraction  at  the  beginning 
of  the  antrum  completely  divides  the  gastric  cavity  into  two  parts. 
This  same  division  of  the  stomach  into  two  parts  at  the  transverse 
band  is  to  be  seen  when  mustard  is  given.  Now,  although  the 
waves  are  still  running  over  the  antrum,  the  whole  pre-antral 


EFFECT  OF  NERVOUS  DISTURBANCES.  207 

part  of  the  stomach  is  fully  relaxed.  A  flattening  of  the  dia- 
phragm and  a  quick  jerk  of  the  abdominal  muscles,  accompanied 
by  the  opening  of  the  cardia,  next  force  the  contents  of  the  fundus 
into  the  esophagus.  As  the  spasmodic  contractions  of  the  abdomi- 
nal muscles  are  repeated,  the  gastric  wall  again  tightens  around 
the  contained  food.  Cannon  has  seen  antiperistalsis  but  once, 
when  a  constriction  started  at  the  pylorus  and  ran  back,  over  the 
antrum,  completely  obliterating  the  antral  cavity. 

In  the  discussion  of  the  movements  of  the  stomach  we  have 
quoted  largely  from  the  paper  of  Cannon,  and  desire  here  to 
express  our  admiration  of  what  we  regard  as  one  of  the  most 
valuable  contributions  to  the  physiology  of  the  stomach  since  the 
time  of  Dr.  Beaumont,  and  in  concluding  this  part  of  the  subject 
we  quote  the  following  statement  and  summary.  He  says : 

"  Although  my  observations  do  not  support  their  (Beaumont 
and  Brinton)  theories  of  mixing  currents  running  throughout  the 
stomach,  they  still  show  that  the  pyloric  portion  is  an  admirable 
device  for  bringing  all  of  the  food  under  the  influence  of  the 
glandular  secretions  of  that  organ.  For,  when  a  constriction 
occurs,  the  secretory  surface  enclosed  by  the  ring  is  brought  close 
around  the  food  lying  within  the  ring  in  the  axis  of  the  stomach. 
As  this  constriction  passes  on,  fresh  areas  of  glandular  tissue  are 
continuously  pressed  in  around  the  narrow  orifice.  And  also,  as 
the  constriction  passes  on,  a  thin  stream  of  gastric  contents  is 
continuously  forced  back  through  the  orifice  and  thus  past  the 
mouths  of  the  glands.  The  result  of  this  ingenious  mechanism 
is  that  every  part  of  the  secretory  surface  of  the  pyloric  portion 
is  brought  near  to  every  bit  of  food  before  the  latter  leaves  the 
stomach,  a  half  hundred  times  or  more." 

"Summary. — 1.  By  mixing  a  harmless  powder,  subnitrate  of 
bismuth,  with  the  food,  the  movements  of  the  stomach  can  be 
seen  by  means  of  the  Rontgen  rays. 

"  2.  The  stomach  consists  of  two  physiologically  distinct  parts  : 
The  pyloric  part  and  the  fundus ;  over  the  pyloric  part,  while 
food  is  present,  constriction-waves  are  seen  continually  coursing 
toward  the  pylorus ;  the  fundus  is  an  active  reservoir  for  the  food, 
and  squeezes  out  its  contents  gradually  into  the  pyloric  part. 

"  3.  The  stomach  is  emptied  by  the  formation,  between  the 
fundus  and  the  antrum,  of  a  tube  along  which  constrictions  pass. 
The  contents  of  the  fundus  are  pressed  into  the  tube,  and  the 
tube  and  antrum  slowly  cleared  of  food  by  the  waves  of  con- 
striction. 

"4.  The  food  in  the  pyloric  part  is  first  pushed  forward  by 
the  running  wave,  and  then,  by  pressure  of  the  stomach-wall,  is 
returned  through  the  ring  of  constriction  ;  thus  the  food  is 
thoroughly  mixed  with  gastric  juice,  and  is  forced  by  an  oscil- 
latory progress  to  the  pylorus. 


208  STOMACH  DIGESTION. 

"  5.  The  food  in  the  fundus  is  not  moved  by  peristalsis,  and 
consequently  is  not  mixed  with  the  gastric  juice ;  salivary  diges- 
tion can  therefore  be  carried  on  in  this  region  for  a  considerable 
period  without  being  stopped  by  the  acid  gastric  juice. 

"  6.  The  pylorus  does  not  open  at  the  approach  of  every  wave, 
but  at  irregular  intervals.  The  arrival  of  a  hard  morsel  causes 
the  sphincter  to  open  less  frequently  than  normally,  thus  mate- 
rially interfering  with  the  passage  of  the  already  liquefied  food. 

"  7.  The  solid  food  remains  in  the  antrum  to  be  rubbed  up  by 
the  constrictions  until  triturated,  or  to  be  softened  by  the  gastric 
juice,  or  later  it  may  be  forced  into  the  intestine  in  the  solid 
state. 

"  8.  The  constriction-waves  have,  therefore,  three  functions : 
The  mixing,  trituration,  and  the  expulsion  of  the  food. 

"  9.  At  the  beginning  of  vomiting  the  gastric  cavity  is  separated 
into  two  parts  by  a  constriction  at  the  entrance  to  the  antrum ; 
the  cardiac  portion  is  relaxed,  and  the  spasmodic  contractions  of 
the  abdominal  muscles  force  the  food  through  the  opened  cardia 
into  the  esophagus. 

"  10.  The  stomach  movements  are  inhibited  whenever  the  cat 
shows  signs  of  anxiety,  rage,  or  distress." 

Excretory  Function  of  the  Stomach.— The  excretion  of 
morphin  and  the  venom  of  snakes  by  the  gastric  and  intestinal 
mucous  membrane,  when  they  have  been  subcutaneously  injected 
into  the  body,  suggests  that  this  power  of  excretion  may  under 
some  circumstances  be  an  important  function  of  the  gastro-intestinal 
tract.  Experiments  with  cesium  and  strontium  have  demonstrated 
that  they  are  eliminated  by  the  same  channel.  Iron  may  also  be 
eliminated  by  the  action  of  the  intestinal  epithelium. 

Effect  of  Nervous  Disturbances  upon  Gastric  Diges- 
tion.— It  is  a  matter  of  common  experience  that  fear,  worry, 
anger,  the  reception  of  unexpected  news,  either  joyous  or  sorrowful, 
will  oftentimes  seriously  interrupt  gastric  digestion.  In  the  case 
of  St.  Martin,  Dr.  Beaumont  observed  that  when  his  temper  was 
irritated  the  secretion  of  gastric  juice  was  greatly  interfered  with 
or  even  suspended.  Unusual  fear  or  a  condition  of  fever  would 
produce  the  same  results.  Cannon  observed  that  when  the  cats 
that  were  the  subjects  of  his  experiments  were  angry,  or  when 
their  breathing  was  stopped  by  preventing  the  entrance  of  air 
into  the  air-passages,  there  was  a  total  suspension  of  the  motor 
activities  of  the  stomach  together  with  a  relaxation  of  the  antral 
fibers. 

Self-digestion  of  the  Stomach.— One  of  the  interesting 
and  still  unexplained  physiologic  enigmas  is :  Why  does  not  the 
stomach,  which  is  proteid  in  its  nature,  undergo  self-digestion 
during  life?  It  is  known  that  when  death  takes  place  during  the 
period  of  active  stomach  digestion,  erosion  of  the  mucous  membrane, 
and  even  perforation  of  the  wall  of  the  stomach,  may  occur.  As 


DURATION  OF  STOMACH  DIGESTION.  209 

this  takes  place  at  the  most  dependent  portion,  where  the  gastric 
juice  naturally  gravitates,  the  explanation  is  simple.  But  if  this 
self-digestion  can  occur  after  death,  why  not  during  life?  No 
satisfactory  answer  to  this  question  has  yet  been  given,  although 
many  theories  have  been  advanced.  One  of  these  was,  that  there 
was  in  living  things  the  "  principle  of  life,"  and  that  so  long  as 
this  principle  existed  it  exercised  a  protecting  influence ;  but  the 
fallacy  of  this  theory  was  made  apparent  when  it  was  shown  that 
the  leg  of  a  living  frog,  passed  through  a  fistula  in  a  dog's  stomach, 
did  undergo  digestion.  Still  another  theory  was  that  the  gastric 
juice  could  act  only  when  it  contained  the  requisite  amount  of 
hydrochloric  acid,  and  that  its  acidity  was  neutralized  by  the 
alkaline  blood,  so  that  the  stomach,  so  long  as  life  existed  and 
blood  was  flowing  through  its  vessels,  could  not  be  digested.  But 
while  this  might  explain  the  non-digestion  of  the  stomach  by  the 
gastric  juice,  it  would  not  account  for  the  non-digestion  of  the 
intestine,  which  is  also  permeated  by  alkaline  blood,  but  whose 
digestive  fluids  are  likewise  alkaline.  The  presence  of  mucus  has 
been  regarded  by  some  as  protecting  the  underlying  mucous  mem- 
brane from  the  action  of  the  gastric  juice,  while  others  have 
attributed  the  same  functions  to  the  epithelium  which  covers  it. 
As  a  matter  of  fact,  no  explanation  has  as  yet  been  given  which 
is  perfectly  satisfactory. 

Duration  of  Stomach  Digestion.— The  duration  of  stom- 
ach digestion  is  variable,  and  depends  upon  several  circumstances, 
among  which  is  the  composition  of  the  stomach-contents.  Some 
kinds  of  food  remain  in  the  stomach  longer  than  others.  Stomach 
digestion  may  in  general  be  said  to  be  from  one  and  a  half  to  five 
and  a  half  hours.  The  following  table  contains  a  list  of  some  of 
the  substances  with  which  Dr.  Beaumont  experimented,  and  the 
length  of  time  they  remained  in  the  stomach  : 

Kind  of  food.  Time. 

Pigs'  feet  and  tripe 1    hour. 

Salmon 1        " 

Milk 2    hours. 

Potato,  roasted      2 

Roast  turkey , 2£ 

Soft-boiled  eggs 2j 

Beefsteak,  broiled 2j 

Hard-boiled  eggs 3- 

Potatoes,  boiled 3£ 

Pork,  boiled 41.     « 

"       roasted 51.     " 

The  above  table,  and  others  of  like  nature,  are  to  be  very 
cautiously  made  use  of  in  determining  the  digestibility  of  the 
different  foods.  The  observations  here  recorded  simply  indicate 
the  length  of  time  the  respective  articles  remained  in  the  stomach, 
and  nothing  more.  Substances  are  digested  when  they  are  in 
condition  to  be  absorbed,  and  not  until  then.  Whenever  any 
u 


210  STOMACH  DIGESTION. 

portion  of  the  food  is  rendered  sufficiently  liquid,  it  is  liable  to 
pass  out  from  the  stomach,  although  there  are  other  factors  than 
this  liquid  character  of  the  food.  If  two  different  articles  of  food 
were  in  the  stomach  at  the  same  time,  one  might  pass  out  from 
that  organ  into  the  small  intestine  in  one  hour,  while  the  other 
might  remain  in  the  stomach  two  hours.  From  this  fact  alone  one 
would  not  be  justified  in  assuming  that  the  one  substance  was 
twice  as  digestible  as  the  other,  for  the  former  might  not  at  the 
time  it  left  the  stomach  have  been  prepared  for  absorption,  but 
might  require  several  hours  for  such  a  change  after  it  reached 
the  small  intestine ;  while  the  latter,  although  it  remained  in  the 
stomach  an  hour  after  the  former  had  left  it,  might  at  the  time  it 
left  the  stomach  have  been  in  a  condition  to  pass  at  once  into  the 
blood. 

The  practical  use  of  tables  showing  the  length  of  time  that 
different  substances  remain  in  the  stomach  seems  to  be  to  deter- 
mine of  what  the  food  should  consist  when  this  organ  is  unable 
to  perform  its  function  in  a  normal  manner,  and  it  is  considered 
wise  to  lighten  its  labors  as  much  as  possible.  For  this  purpose 
such  food  should  be  selected  as  will  remain  in  the  stomach  but  a 
short  time,  even  though  it  pass  out  in  an  undigested  state,  for,  as 
will  hereafter  be  seen,  the  peptonizing  function  may  be  carried  on 
in  the  small  intestine  as  in  the  stomach ;  and  in  a  disabled  con- 
dition of  the  latter  organ,  and  even  when  this  is  absent,  the  former 
will  supplement  it.  In  the  dog,  so  thoroughly  may  digestion  be 
performed  by  the  intestines  alone,  without  the  aid  of  the  stomach, 
that  this  latter  has  been  almost  completely  removed,  yet  the  animal 
has  been  kept  alive  in  excellent  health  and  strength.  The  first 
removal  of  this  kind  was  by  Czerny,  and  the  dog  lived  for  five 
years.  After  death  it  was  examined,  and  it  was  found  that  in 
the  operation  all  the  organ  had  been  removed  except  a  small 
portion  of  the  cardiac  extremity.  The  animal  ate  all  kinds  of 
food  and  thrived  on  them. 

Trial-meals. — Some  light  has  been  thrown  on  this  question  of  the 
duration  of  stomach  digestion  by  the  application  of  methods  of 
obtaining  and  examining  the  contents  of  the  stomach  for  diagnostic 
purposes.  To  ascertain  how  far  the  digestive  process  is  interfered 
with,  trial-meals  are  given.  The  stomach  is  evacuated  by  means 
of  a  soft-rubber  stomach-pipe  after  a  proper  time,  and  inspection 
shows  to  what  stage  the  process  of  digestion  has  advanced. 

Hemmeter  recommends  the  following  plan  of  procedure  :  At 
8  A.M.  should  be  given  one  small  piece  of  beef,  scraped  and 
broiled  ==  80  gm. ;  1  soft-boiled  egg ;  30  gm.  of  boiled  rice ;  1 
glass  of  milk  =  250  c.c. ;  and  a  piece  of  bread.  Four  or  five 
hours  later  an  Ewald  test-meal,  consisting  of  a  roll  or  a  piece  of 
wheat  bread  and  500  c.c.  of  water,  or  tea  without  milk  or  sugar, 
is  given,  and  one  hour  after  this  the  stomach-contents  are  drawn. 
In  giving  a  test-meal,  Hemmeter  recommends  that  good  chewing 


REMOVAL   OF  THE  HUMAN  STOMACH.  211 

should  be  insisted  on,  and  all  food-substances  should  be  very  finely 
cut  up,  so  that  they  cannot  plug  up  the  tube,  even  if  not  digested. 
The  advantages  claimed  for  this  test-meal  are  that  after  drawing 
it,  in  a  large  number  of  instances,  the  conditions  of  gastric 
rnotility  and  secretion  may  be  recognized  before  any  analysis  is 
made ;  then,  a  disappearance  of  the  entire  breakfast-meal  points 
to  a  normal  digestion.  "Absence  of  all  proteids — beef  and  egg — 
and  presence  of  considerable  carbohydrates — rice  and  bread — 
point  to  hyperchlorhydria ;  and,  again,  absence  of  all  carbohy- 
drates and  presence  of  some  of  the  beef  and  egg  point  to  hyper- 
chlorhydria, subacidity,  anacidity,  or  achylia.  Presence  of  the 
entire  meal,  with  perhaps  milk  uncurdled,  means  impaired  motility, 
with  atrophy  of  gastric  mucosa,  absence  of  acids,  enzymes,  and 
pro-enzymes.  If  the  entire  meal  has  disappeared,  the  status  of 
the  gastric  secretions  may  be  ascertained  from  the  Ewald  test- 
meal,  which  is  still  present." 

In  his  discussion  of  the  physiology  of  gastric  peristalsis,  Hem- 
meter  concludes  as  follows :  "  It  is  necessary  to  distinguish  the 
movements  of  the  (1)  fundus,  (2)  pre-antral  portion,  (3)  antrum, 
and  (4)  pyloric  sphincter.  (1)  The  motor  apparatus  of  the  stom- 
ach is  represented  by  its  muscular  fibers.  When  these  are  most 
developed,  the  peristalsis  is  strongest ;  when  they  are  least  devel- 
oped, it  is  weakest.  (2)  The  fundus  has  a  thin  muscular  devel- 
opment; hence  its  peristalsis  is  insignificant,  and  consists  in 
squeezing  its  contents  into  the  tubular  pre-antrum  or  prepyloric 
portion.  (3)  Waves  of  constriction  along  this  pre-antrum  force 
the  food  forward  and  backward  through  this  portion  until  a 
mightier  wave-impulse  sweeps  it  into  the  muscular  ampulla  just 
in  front  of  the  pylorus,  the  autrum  pylori.  (4)  The  final  ex- 
pression into  the  duodenum  is  executed  by  the  antrum,  which  may 
contract  as  a  whole  or  form  into  two  spherical  muscular  ventricles 
by  a  constriction  (rarely).  (5)  A  food  circulation,  in  the  sense  of 
Beaumont  and  Brinton,  does  not  occur." 

Removal  of  the  Human  Stomach. — The  first  total  re- 
moval of  the  human  stomach  was  performed  by  Dr.  Connor,  of 
Cincinnati,  Ohio,  U.  S.  A.,  in  1885,  the  patient  dying  very  soon 
after  the  operation.  Langenbuch,  Schuchardt,  and  others  have 
also  removed  the  stomach,  and  inasmuch  as  in  these  cases  only  a 
small  portion  was  left,  and  that  a  portion  which  could  perform 
no  function,  these  cases  may  be  regarded,  from  a  physiologic 
standpoint,  as  complete  removals.  In  Schuchardt's  case,  the 
patient  lived  two  and  one-half  years,  and  was  apparently  in  ex- 
cellent health. 

There  are  two  cases,  however,  of  complete  ablation  of  this 
organ  which  are  of  great  interest  physiologically,  and  of  which 
many  important  details  are  accessible,  and  these  it  is  our  purpose 
to  describe  somewhat  minutely.  One  occurred  in  Zurich,  Switzer- 
land, and  the  other  in  San  Francisco,  California,  U.  S.  A. 


212  STOMACH  DIGESTION. 

Schlatter's  Case.— On  September  6,  1897,  Carl  Schlatter  of 
the  University  of  Zurich,  performed  on  a  woman,  aged  fifty-six 
years,  the  operation  of  esophago-enterostomy ;  the  patient  being 
the  subject  of  diffuse  carcinoma  of  the  entire  stomach.  In  this 
operation  the  entire  stomach  was  removed  and  the  esophagus 
attached  to  the  jejunum,  it  having  been  found  impossible  to 
approximate  the  esophagus  and  duodenum.  We  are  indebted  to 
the  New  York  Medical  Record  of  December  25,  1897,  and  .March 
18,  1899,  for  the  history  of  this  case.  This  article  contains  intro- 
ductory remarks  by  Dr.  E.  C.  Wendt,  of  New  York,  and  a  descrip- 
tion of  the  operation  and  subsequent  history  of  the  case  by  Dr. 
Schlatter. 

So  completely  was  the  stomach  removed,  that  at  the  cardiac 
end  of  the  extirpated  organ  esophageal  tissue  was  demonstrated 
to  be  present,  as  was  also  the  pylorus  at  the  other  extremity. 
The  patient  lived  fourteen  months  after  the  operation,  during 
twelve  of  which  she  was  free  from  suffering  and  gained  in  weight. 
Her  death  was  due  to  general  cancerous  infection  proceeding  from 
a  carcinoma  of  the  mesenteric  lymph-glands.  It  is  the  opinion 
of  those  familiar  with  the  case  that  it  was  not  attributable  in  any 
degree  to  the  operation  nor  to  absence  of  the  stomach. 

Shortly  after  the  operation  an  enema  containing  brandy  and 
two  eggs  was  given.  The  first  day  after  the  operation  two 
enemata  were  administered  containing  milk,  eggs,  and  brandy, 
and  later  in  the  day  a  small  quantity  of  tea  and  milk  by  the 
mouth,  which  was  retained.  On  the  second  day  the  enemata  were 
not  retained,  and  claret  wine  was  given  by  the  mouth.  On  the 
third  day,  small  quantities  of  milk,  eggs,  bouillon,  and  wine  were 
given  by  the  mouth,  and  pepsin  and  hydrochloric  acid.  On  the 
seventh  day  a  little  scraped  meat  was  given,  and  the  following 
day  the  bowels  moved  for  the  first  time.  Occasionally  there  was 
some  regurgitation  of  milk,  but  no  actual  vomiting  until  the  tenth 
day  ;  on  that  day,  and  subsequently,  the  patient  took  the  following 
food :  7  A.M.,  a  cup  of  milk  with  one  egg ;  9.30  A.M.,  same  ; 
dinner  (time  not  stated),  very  soft  scraped  meat  or  cup  of  thin 
gruel  with  an  egg ;  4  P.M.,  cup  of  milk  with  egg ;  7.30  P.M.,  cup 
of  milk  or  gruel.  Besides  these,  she  took  tea  and  Malaga  wine, 
amounting  in  the  course  of  the  day  to  from  140  c.o.  to  200  c.c. 

On  the  tenth  day  the  patient  vomited  for  the  first  time  since 
the  operation.  The  vomiting  was  preceded  by  nausea,  and  was 
apparently  superinduced  by  the  patient  having  witnessed  a  change 
of  dressing  in  a  neighboring  surgical  case.  There  was  a  good  deal 
of  retching,  and  about  200  c.c.  of  bilious  and  slightly  acrid  fluid 
were  ejected.  On  the  twentieth  day  she  ate  half  a  chicken,  and 
later  milk  and  an  egg.  About  three  hours  after  eating  the  chicken, 
and  one  hour  after  the  milk  and  egg,  she  vomited  about  280  c.c. 
of  milk  and  meat-fibers.  This  was  accompanied  by  retching  and 
marked  contraction  of  the  abdominal  muscles.  On  subsequent 


REMOVAL   OF  THE  HUMAN  STOMACH.  213 

days  attacks  of  vomiting  recurred.  One  of  these  was  about  one 
month  after  the  operation,  and  an  examination  of  the  ejected 
matter  showed  it  to  be  acid  in  reaction,  due  to  the  lactid  acid,  no 
free  hydrochloric  acid  being  found.  Trypsin,  bile-acids,  and  bile- 
pigments  were  also  found. 

From  the  time  of  the  operation  there  was  a  continued  increase 
in  weight,  as  shown  by  the  following  table : 

Table  showing  Weight  of  Patient  after  Operation. 

f       .  ,  .  Actual  weight  in  Increase  in 

Date  of  weighing.  grams?  grams. 

October    5 33,600 

October  11 33,750  150 

October  18 35,260  1510 

October  25 35,500  240 

October  29 36,000  500 

November    5 36,200  200 

November  19 36,500  300 

December  3 37,500  1000 

December  9 37,500 

The  patient  was  not  actually  weighed  on  the  day  of  the  opera- 
tion, but  the  minimum  increase  from  September  6  to  October  5 
has  been  estimated  at  2000  gm.  (2  kgm.). 

We  cannot  better  conclude  the  history  of  this  most  remark- 
able and  interesting  case  than  by  quoting  the  conclusions  of  Dr. 
Schlatter  and  Dr.  Wendt. 

Dr.  Schlatter  says : 

"  Clinical  Observations  in  Connection  with  the  Obliteration  of 
all  Gastric  Functions  after  the  Operation. — There  being  no  food- 
receptacle  after  ablation  of  the  stomach,  it  became  obligatory  to 
feed  my  patient  at  first  with  minute  quantities  of  food,  given  at 
short  intervals.  The  results  of  this  method  of  procedure  were  in 
all  respects  happy  ones.  Quantities  of  food  approaching  ten  ounces 
seemed  to  excite  vomiting.  So,  too,  cold  fluids  resulted  in  diar- 
rheal  discharges,  and  may  have  been  partly  responsible  for  the  rise 
in  temperature  observed  for  some  little  time  after  the  operation. 

"  Keeping  in  mind  the  absence  of  mechanical  function,  the 
patient's  dietary  was  at  first  a  strictly  fluid  one.  But  as  early  as 
the  second  week  after  removal  of  the  stomach  semisolid  and  even 
solid  food  was  allowed.  It  was  retained  and  digested  without  dis- 
comfort. The  patient  having  only  a  single  tooth,  mastication  was, 
of  course,  quite  imperfect,  otherwise  it  seems  to  me  possible  that 
an  ordinary  mixed  diet  might  have  succeeded  at  a  still  earlier  date. 

"  Some  weeks  after  the  operation  the  patient's  ordinary  daily 
dietary  was  as  follows :  At  regular  intervals  of  from  two  to  three 
hours  she  took  milk,  eggs,  thin  gruel  or  pap,  tea,  meat,  rolls, 
butter,  and  Malaga  wine.  The  daily  quantity  amounted  to  one 
quart  of  milk,  two  eggs,  two  to  three  ounces  of  pap  or  gruel, 
seven  ounces  of  meat,  seven  ounces  of  oatmeal  or  barley-water 


214  STOMACH  DIGESTION. 

(as  thick  almost  as  gruel),  one  cup  of  tea,  two  rolls,  and  half  an 
ounce  of  butter. 

"  Personally  I  felt  most  concerned  about  the  obliteration  of  all 
chemical  activity  on  the  part  of  the  absent  stomach.  I  soon  per- 
ceived that  adding  pepsin  and  hydrochloric  acid  to  the  food  was 
theoretically  as  inadmissible  as  it  had  been  found  practically  value- 
less. The  alkaline  fluids  of  the  intestine  at  once  neutralized  the 
acid,  and  rendered  the  pepsin  inert. 

"  Fortunately,  it  soon  became  apparent  that,  despite  the  absence 
of  acid  pepsin,  proteids  were  readily  assimilated  in  the  intestinal 
tract. 

"  Does  Gastric  Acidity  Influence  the  Decomposition  of  Intestinal 
Contents? — This  moot  question  received  contributory  elucidation 
by  the  careful  study  of  the  patient's  discharges  after  the  operation. 
The  urine  and  feces  were  examined  every  day  at  the  chemical 
laboratory  of  the  university.  Products  of  abnormal  intestinal  fer- 
mentation or  decomposition  (skatoxyl  and  indoxyl)  were  either 
not  at  all  found,  or  else  discovered  only  in  traces. 

"  These  observations  tend  to  corroborate  the  views  of  von 
Noordeii,  while  they  negative  the  opinion  held  by  Kast  and  Was- 
butski.  The  most  recent  results  of  laboratory  experiments 
announced  from  Professor  Baumann's  institute,  viz.,  that  hydro- 
chloric acid  inhibits  intestinal  decomposition,  thus  received  no 
support  from  actual  observations  in  the  living  human  subject. 

"  Does  Removal  of  the  Stomach  Affect  the  Rapidity  of  Intestinal 
Propulsion  ? — Observations  on  this  point  are  still  being  made,  and 
at  the  present  time  I  am  unable  to  present  any  very  definite  con- 
clusions. The  patient  objected  to  swallowing  charcoal.  Huckle- 
berries were  at  three  different  times  found  in  the  passages  twenty- 
four  hours  after  having  been  swallowed. 

"  The  Urine  after  the  Operation. — Apart  from  a  daily  recurring 
diminution  in  the  quantity  of  excreted  chlorids,  the  urine  of  this 
woman  has  remained  normal  since  ablation  of  her  stomach.  The 
daily  excretion  of  chlorid  of  sodium  has  been  found  to  vary  be- 
tween the  limits  of  0.6  per  cent,  and  0.95  per  cent.  It  should  be 
stated  in  this  connection,  however,  that,  complying  with  the  wish 
of  the  patient,  her  food  is  prepared  with  less  salt  than  that  of  the 
other  ward  patients. 

"  Miwoscopic  Examination  of  the  Feces. — The  stools  were  well 
formed,  of  normal  consistency,  and  light  yellow  in  color.  The 
microscope  showed  large  numbers  of  fat-globules,  and  fatty 
crystals,  some  undigested  vegetable-fibers,  but  no  undigested 
animal-fibers  or  connective  tissue.  Large  quantities  of  triple 
phosphates  were  observed.  The  number  of  micro-organisms  was 
normal.  Altogether,  repeated  examinations  revealed  no  note- 
worthy departure  from  a  condition  of  perfect  health. 

"  Vomiting  ivithout  a  Stomach. — How  can  a  person  vomit  with- 
out a  stomach?  No  matter  what  theoretic  physiologic  notions 


REMOVAL   OF  THE  HUMAN  STOMACH.  215 

we  may  have  imbibed  from  lectures  and  text-books,  the  woman 
under  observation  had  repeated  attacks  of  ordinary  nausea,  retch- 
ing, and  vomiting.  We  must  needs  conclude,  therefore,  that  the 
role  of  the  stomach  (i.e.,  its  antiperistaltic  efficacy)  in  this  direction 
has  been  very  much  overrated.  While  the  vomited  substances 
showed  an  acid  reaction,  this  was  not  due  to  the  presence  of  free 
hydrochloric  acid. 

"  In  view  of  the  fact  that  the  patient  ejected  as  much  as  thirty 
ounces  at  one  time,  it  seems  reasonable  to  suppose  that  the  remain- 
ing portion  of  the  duodenum  may  have  already  begun  to  show 
distention  sufficient  to  produce  a  sort  of  compensatory  receptacle 
for  food — perhaps  nature's  attempt  in  the  direction  of  the  new 
formation  of  a  stomach. 

"  In  endeavoring  to  explain  vomiting  without  a  stomach,  we 
should  remember  that  the  act  itself  is  far  from  being  a  simple 
process.  It  is  due  to  nervous  action  on  a  complex  motor  appa- 
ratus, consisting  of  pharynx,  esophagus,  stomach,  diaphragm,  and 
abdominal  muscles. 

"  It  is  not  surprising,  therefore,  to  have  witnessed  in  this 
woman  an  ordinary  attack  of  bilious  vomiting  superinduced  by 
a  mere  physical  disturbance." 

Conclusions  by  Dr.  E.  C.  Wendt. — "  While  it  would  be  mani- 
festly unfair  to  indulge  in  sweeping  generalizations  on  the  strength 
of  this  single  case,  so  bodly  rescued  and  ably  described  by  Dr. 
Schlatter,  it  seems  at  least  justifiable  to  formulate  the  following 
conclusions : 

"  1.  The  human  stomach  is  not  a  vital  organ. 

"  2.  The  digestive  capacity  of  the  human  stomach  has  been 
considerably  overrated. 

"  3.  The  fluids  and  solids  constituting  an  ordinary  mixed  diet 
are  capable  of  complete  digestion  and  assimilation  without  the  aid 
of  the  human  stomach. 

"  4.  A  gain  in  the  weight  of  the  body  may  take  place  in  spite 
of  the  total  absence  of  gastric  activity. 

"  5.  Typical  vomiting  may  occur  without  a  stomach. 

"6.  The  general  health  of  a  person  need  not  immediately 
deteriorate  on  account  of  removal  of  the  stomach. 

"  7.  The  most  important  office  of  the  human  stomach  is  to 
act  as  a  reservoir  for  the  reception,  preliminary  preparation, 
and  propulsion  of  food  and  fluids.  It  also  fulfils  a  useful  pur- 
pose in  regulating  the  temperature  of  swallowed  solids  and 
liquids. 

"  8.  The  chemical  functions  of  the  human  stomach  may  be 
completely  and  satisfactorily  performed  by  the  other  divisions  of 
the  alimentary  canal. 

"  9.  Gastric  juice  is  hostile  to  the  development  of  many  micro- 
organisms. 

"  10.  The  free  acid  of  normal  gastric  secretions  has  no  power 


FIG.  112.— Brigham's  case  of  removal  of  the  stomach :  patient  seven  weeks  after 

the  operatiou. 


FIG.  113.— Anterior  view  of  stomach  removed  from  patient  in  the  preceding  figure 

(Brigham). 


REMOVAL   OF  THE  HUMAN  STOMACH. 


217 


to  arrest  putrefactive  changes  in  the  intestinal  tract.    Its  antiseptic 
and  bactericide  potency  has  been  overestimated." 

Brigham's  Case. — Dr.  Charles  B.  Brigham,  of  San  Francisco, 
California,  on  February  24,  1898,  completely  removed  the  stom- 
ach from  a  woman,  sixty-six  years  of  age,  affected  with  adeno- 
carcinoma  of  the  stomach,  involving  one-half  the  organ,  and  sub- 
sequently connected  the  esophagus  with  the  duodenum,  thus 
performing  the  operation  of  esophago-duodenostomy.  This  case 
is  described  by  Dr.  Brigham  in  the  Boston  Medical  and  Surgical 
Journal  of  May  5,  1898,  and  to  this  journal  we  are  indebted  for 
the  details. 

In  this  case  the  operator  was  able  to  bring  the  duodenum 
up  to  the  esophagus,  which  was  not  possible  in  Schlatter's 
case,  and  the  two  were  approximated  by 
means  of  a  Murphy  button  (Fig.  114) 
instead  of  by  sutures.  Fig.  113  shows 
anterior  view  of  the  diseased  organ  after 
removal. 

After  the  operation  the  patient  was  nour- 
ished at  first  by  enemata  of  brandy  and  water, 
eggs,  milk,  and  broths.  During  the  evening 
of  the  day  of  the  operation  the  patient  vom- 
ited some  bloody  mucus.  On  the  following 
day  hot  water  was  given  by  the  mouth, 
which  relieved  the  intense  thirst.  On  the 
second  day  claret  and  water,  hot  black 
coffee  or  chicken-broth  was  given,  but 
after  two  teaspoonfuls  there  was  no  desire 
for  more.  On  the  third  day  double  this 
quantity  was  taken  each  time,  and  on  this 
day  the  bowels  were  moved  for  the  first 
time.  The  nutrient  enemata  were  given 
every  four  hours  up  to  the  fourth  day, 
when  they  were  discontinued.  On  the 
sixth  day  she  was  taking  about  22  c.c.  at  each  feeding,  but  could 
take  no  more.  This  quantity,  however,  was  gradually  increased. 
About  three  weeks  after  the  operation  she  took  for  breakfast  a 
cup  of  coffee  with  milk,  a  soft-boiled  egg,  and  a  third  of  a  baked 
apple  ;  at  noon,  a  cup  of  green-pea  soup,  a  dozen  small  oysters, 
and  an  ounce  of  milk  ;  in  the  afternoon,  some  orange-jelly,  one 
raw  egg,  half  a  cup  of  pea  soup,  and  a  dozen  oysters  ;  in  the  even- 
ing, half  a  cup  of  asparagus  soup,  with  14  c.c.  of  whiskey  and  42 
c.c.  of  wine.  During  convalescence  the  patient  vomited  food  once, 
and  on  another  occasion  some  mucus.  About  a  month  after  the 
operation  she  complained  of  hunger,  and  ate  a  squab.  About  ten 
days  later  she  ate  in  one  day  the  following :  At  6.30  A.M.,  cup  of 
coffee  and  a  raw  egg ;  at  10  A.M.,  two  dozen  small  oysters  and  a 


218  STOMACH  DIGESTION. 

bowl  of  broth ;  at  1  P.M.,  half  a  broiled  chicken  with  toast,  and 
stewed  strawberries ;  at  5  P.M.,  half  a  broiled  chicken,  two  slices 
of  toast,  and  a  cup  of  tea.  During  that  week  she  gained  six 
pounds. 

In  concluding  the  history  of  this  case  Dr.  Brigham  writes : 

"  In  the  treatment  of  this  case  no  attempt  has  been  made  to 
predigest  the  nourishment  which  was  given  to  the  patient.  The 
precaution  was  taken,  however,  to  supply  easily  digested  food  ; 
and  when  meat  was  allowed  it  was  cut  in  very  small  pieces.  The 
food  was  taken  slowly,  whether  liquid  or  solid.  It  is  no  hardship 
for  the  patient  to  live  on  simple  food,  for  she  has  done  so  all  her 
life ;  and  especially,  as  age  has  advanced,  has  been  obliged  to  eat 
food  that  required  the  least  chewing.  The  food  was  given  of 
medium  temperature ;  water  was  taken  as  it  came  from  the  pipe 
and  wine  as  it  stood  in  the  room  ;  iced  cream,  of  which  the  patient 
was  particularly  fond,  was  taken  slowly  so  that  it  dissolved  in  the 
mouth  before  it  was  swallowed.  At  first  everything  was  too  salt ; 
as  the  patient  got  well  she  wished  salt  on  both  eggs  and  oysters. 
The  amount  of  flatus  in  the  bowels  was  enough  to  cause  pain  only 
a  few  times  in  the  early  part  of  her  illness.  The  urine  has  been 
normal  throughout.  Never  since  the  operation  has  any  undigested 
food  been  seen  in  the  movements  from  the  bowels,  and  for  the 
most  part  these  have  been  wholly  or  partly  formed.  The  patient 
has  vomited  but  a  few  times  since  the  operation  ;  twice  after  etheri- 
zations, twice  after  some  laxative  had  been  given,  once  after  the 
button  left  its  place,  and  twice  after  coughing — not  more  than  six 
ounces  at  any  one  time,  generally  much  less.  On  three  or  four 
occasions  a  mouthful  of  food  would  be  regurgitated — an  oyster, 
some  shreds  of  meat,  or  a  few  teaspoonfuls  of  coffee.  As  a  usual 
thing  the  food  was  well  retained  and  well  digested." 

On  January  1,  1900,  Dr.  Brigham 'wrote  to  the  author:  "I 
am  very  glad  to  say  that  Mrs.  M.  is  in  excellent  health,  with  no 
sign  whatever  of  a  return  of  the  disease.  On  seeing  her  no  one 
would  ever  believe  that  she  had  undergone  any  surgical  operation, 
much  less  the  removal  of  the  entire  stomach.  She  returned  home 
seven  weeks  after  the  operation ;  then  she  took  five  meals  a  day, 
consisting  mainly  of  soups,  oysters,  eggs,  milk-toast,  baked 
apples,  stewed  prunes,  iced  cream,  and  strawberries.  Little  by 
little  she  chose  what  she  liked — potatoes,  peas,  beans,  lamb-chops, 
chicken,  and  fish. 

"  I  have  always  allowed  her  to  choose  her  food,  thinking  that 
the  success  of  the  operation  would  be  the  better  demonstrated. 

"  For  nearly  a  year  she  has  kept  house  for  herself,  doing  all 
her  own  work ;  finding  ample  time  to  visit  her  grandchildren, 
who  live  near  by.  She  is  now  in  her  sixty-eighth  year,  and  affirms 
that  if  she  takes  castor  oil  every  ten  days  her  health  is  perfect. 

"  As  to  her  weight,  after  the  first  year  she  weighed  one  hun- 


ACHYLIA   OAStRICA.  219 

dred  and  ten  pounds ;  last  summer  she  gained  two  pounds.     This 
weight  she  keeps  at  the  present  time. 

Since  Dr.  Brigham's  death  in  1 902,  the  author  has  been  unable 
to  obtain  any  further  history  of  this  case. 

Achylia  Gastrica. — The  fact  that  human  beings  can  live 
and  be  apparently  in  perfect  health,  digesting  all  classes  of  food- 
stuffs, and  yet  possessing  no  stomach,  as  is  shown  most  notably  in 
Dr.  Brigham's  case,  makes  it  quite  easy  to  believe  that  a  similar 
normal  condition  may  be  maintained  when  the  stomach  is  present, 
but  a  stomach  which  secretes  no  gastric  juice.  Such  a  condition 
of  permanent  absence  of  the  gastric  secretion  is  termed  achylia 
gastrica.  This  affection  has  been  described  also  under  the  names 
gastritis  glandularis  atrophicans  and  progressive  atrophy  of  the 
stomach.  There  are  some  cases  in  which  the  achylia  is  congenital, 
and  others  in  which  it  comes  on  at  middle  life  and  in  connection 
with  chronic  gastric  catarrh  or  some  other  affection.  The  admin- 
istration of  test-meals  demonstrates  the  absence  of  hydrochloric 
acid,  pepsin,  and  rennin.  Persons  having  achylia  gastrica  are 
often  apparently  in  perfect  health  and  eat  everything  they  wish. 

The  cases  in  which  the  stomach  has  been  totally  removed, 
taken  in  conjunction  with  these  cases  of  achylia  gastrica,  all  point 
to  the  conclusion  that  the  small  intestine  is  capable  of  carrying  on 
all  the  digestive  processes  without  any  aid  from  the  stomach. 

Still,  it  can  hardly  be  supposed  that  the  stomach  is  entirely  a 
superfluous  organ.  Hemmeter,  in  discussing  "The  Logic  of 
Hydrochloric  Acid  Therapy/'  in  American  Medicine,  says : 

"The  cases  frequently  noted  in  patients  without  any  gastric 
secretion  whatever  who  succeed  in  maintaining  their  nitrogen- 
equilibrium  (and  we  have  seen  many  such),  and  the  experiment 
on  the  dog  (Kaiser  and  Czerny),  the  weight  of  which  was  kept  up, 
although  the  largest  portion  of  the  stomach  was  removed,  and 
Brigham's  and  Schlatter's  total  extirpations  of  the  stomach,  con- 
stitute but  a  weak  argument  against  the  therapy  of  HCL  For 
although  such  patients  and  animals  manage  to  get  along  fairly 
well  for  a  time,  it  is  only  under  the  most  careful  and  scientific 
supervision  that  their  health  is  maintained.  Permanent  and 
perfect  health  with  total  absence  of  gastric  secretion  is  rarely 
observed,  except  in  those  who  are  able  to  rest  much  and  have  their 
food  prepared  with  great  care. 

"  These  facts  must  not  be  overlooked  in  considering  the  work 
of  von  Noorden,  which  demonstrated  that  absolute  and  permanent 
deficiency  of  gastric  juice  may  be  accompanied  by  perfect  health. 
This  health  is  perfect  under  the  conditions  mentioned,  but  when 
such  patients  are  taxed  by  work  or  the  diet  is  not  the  usual  one, 
in  my  experience  suffering  invariably  becomes  manifest.  If 
achylia  gastrica  could  really  exist  without  any  subjective  or 
objective  disturbances,  how  is  it  that  so  many  of  these  patients 
consult  the  stomach  specialists  and  are  reported  by  them  in  lit- 


220  STOMACH  DIGESTION. 

erature  ?  When  we  must  work  for  our  living  and  cannot  have 
the  benefit  of  the  dietetic  kitchen  at  all  times,  we  must  have  an 
active  gastric  juice  to  at  least  partially  disinfect  and  dissolve  our 
food,  and  a  person  who  secretes  no  gastric  juice  is  or  soon  becomes 
a  patient. 

"  In  a  recent  article  on  achylia  gastrica,  by  F.  Martius  and  O. 
Lubarsch,  the  authors  arrive  at  the  conclusion  that  neither  simple 
achylia  nor  that  dependent  upon  atrophy  of  the  mucosa  (anadenia) 
can  bring  about  severe  anemic  or  cachectic  conditions,  unless  motor 
insufficiency,  atrophy  of  the  intestinal  mucosa,  or  general  diseases 
(tuberculosis,  lues,  infections,  etc.)  are  added.  Even  if  this  is 
true,  generally  speaking,  it  does  not  disprove  the  statement  that 
absence  of  HC1  in  the  gastric  secretion  compels  the  individual  to 
lead  the  life  of  a  patient,  for  dyspepsia  and  dystrypsia  may  exist 
and  become  severe  without  the  anatomic  changes  spoken  of  by 
Martius  and  Lubarsch.  But,  over  and  beyond  this,  Flint,  Fen- 
wick,  Quincke,  Nothnagel,  Osier,  Kinnicut,  also  Rosenheim  and 
G.  Meyer,  have  described  cases  of  pernicious  anemia  in  which 
atrophy  of  the  gastric  mucosa  was,  at  the  autopsy,  found  to  be 
the  only  organic  disease  existing.  It  is  conceivable  that  the  in- 
testine cannot  persistently  digest  an  amount  of  proteid  sufficient 
to  maintain  the  nitrogen-equilibrium  during  work  ;  that  it  depends 
upon  a  certain  part  of  this  proteolysis  to  be  performed  by  the 
stomach  ;  that  the  acid  gastric  chyme  is  necessary  for  the  stimu- 
lation of  the  duodenal  secretions.  Pawlow  has  proved  experi- 
mentally that  the  gastric  HC1  is  an  important  stimulant  to  the 
secretion  of  pancreatic  juice.  It  is  probable  that  digestion  in  the 
duodenum  is  not  perfect  without  the  acid  proteids,  which,  as  we 
know,  cause  increased  diastasic  action  of  the  pancreatic  juice.  So 
that  we  are  justified  in  concluding  on  experimental  and  clinical 
grounds  that  in  the  absence  of  secretion  of  HC1  in  the  stomach 
the  entire  duodenal  digestion  is  abnormal.'' 

Artificial  Gastric  Juice. — In  addition  to  the  observations 
upon  man  and  lower  animals  already  referred  to,  many  experi- 
ments have  been  carried  on  with  an  artificial  gastric  juice  made 
by  extracting  the  pepsin  from  the  mucous  membrane  of  the  stom- 
ach of  the  pig  with  glycerin,  and  adding  to  this  glycerin-extract 
0.2  per  cent,  of  hydrochloric  acid.  The  results  of  these  experi- 
ments are,  however,  not  to  be  regarded  as  identical  with  those  that 
take  place  in  the  stomach  of  a  living  being.  The  factors  in  the 
problem  are  many,  and  some  of  them  are  still  undetermined. 

Effect  of  Alcohol  on  Digestion.— This  subject  has  already 
been  fully  discussed,  and  the  reader  is  referred  to  p.  159. 


STRUCTURE  OF  THE  SMALL  INTESTINE.  221 

INTESTINAL  DIGESTION. 

The  intestinal  canal  extends  from  the  stomach  to  the  anus,  and 
is  divided  into  the  duodenum  Jejunum,  and  ileum,  which  constitute 
the  small  intestine,  which  is  about  8  meters  in  length,  and  the 
cecum,  colon,  and  rectum,  constituting  the  large  intestine,  having 
together  a  length  of  1.68  meters. 

Structure  of  the  Small  Intestine. — The  duodenum  is  the 
portion  of  the  small  intestine  into  which  the  food  enters  after 
leaving  the  stomach.  It  is  about  30  cm.  in  length  and  5  cm.  in 
diameter,  and  passes  into  the  jejunum,  and  this  in  turn  into  the 
ileum,  the  opening  between  the  ileum  and  the  beginning  of  the 
large  intestine  being  guarded  by  the  ileocecal  valve. 

Coats  of  the  Small  Intestine. — Like  the  stomach,  the  small 
intestine  is  composed  of  four  coats:  1,  serous;  2,  muscular; 
3,  submucous ;  4,  mucous.  As  in  the  stomach,  the  two  coats 
which  have  special  physiologic  interest  are  the  muscular  and  the 
mucous.  The  muscular  coat  is  made  up  of  two  layers :  an  ex- 
ternal or  longitudinal  and  an  inner  or  circular,  between  which  are 
lymphatic  vessels  and  the  plexus  myentericus  of  Auerbach  (Fig. 
115). 

In  the  submucous  coat  are  blood-vessels,  lymphatics,  and  the 
plexus  of  Meissner. 


FIG.  115. — A  portion  of  the  plexus  of  Auerbach  from  stomach  of  cat,  stained  with 
methylene-blue  (intra  vitam),  as  seen  under  low  magnification  (Huber). 

The  mucous,  or  most  internal,  coat  contains  the  following 
structures,  a  knowledge  of  which  is  essential  to  an  understanding 
of  the  physiology  of  this  portion  of  the  digestive  apparatus :  (1) 
valvulse  conniventes  ;  (2)  villi ;  (3)  glands  of  Brunner ;  (4)  glands 
of  Lieberkiihn ;  (5)  solitary  glands ;  (6)  agminated  glands  or 
Peyer's  patches. 


222 


INTESTINAL  DIGESTION. 


Valvulte  Conniventes. — The  mucous  coat  of  the  intestine  is 
arranged  in  folds,  to  which  the  name  valvulce  conniventes  has  been 
given  (Fig.  116).  These  folds,  which  begin  about  2  cm.  below 
the  pylorus,  are  present  throughout  the  length  of  the  small  intes- 
tine, excepting  in  the  lower  part 
of  the  ileum.  They  are  more 
abundant  in  the  upper  half  of 
the  intestine,  where  they  have 
been  counted  to  the  number  of 
600,  than  in  the  lower  half, 
where  only  250  have  been  found, 
making  about  850  in  all.  These 
folds  are  arranged  around  the  FIG.  1 16 -Portion  of  the  wall  of  the 

/>  ,1        .e,       .  .    ,          small  intestine,  laid  open  to  show  the 

Ulterior  OI   tile   intestine  at   right      Valvula>  conniventes  (Brinton). 

angles  to  its  long  axis.     They  do 

not  completely  encircle  it  like  a  ring,  but  vary  in  length,  some 
extending  about  two-thirds  and  others  only  one-third  the  distance 
around.  The  widest  of  them  is  not  more  than  1.5  cm.  in  width, 
projecting  into  the  caliber  of  the  intestine  to  this  extent.  Each 
is  a  double  fold  of  mucous  membrane  with  connective  tissue  be- 
tween, which  so  binds  the  folds  together  that  even  in  the  condi- 
tion of  distention  the  valvulse  conniventes  are  not  obliterated,  as 


FIG  117.-MUCOUS  membrane  of  the  jejunum,  highly  magnified  (schematic): 
11  intestinal  yilh ;  2,  2,  closed  or  solitary  follicles;  3,  3,  orifices  of  the  follicles 
of  Lieberkuhn  (Testut). 

is  the  case  with  the  rugae  of  the  stomach.  By  means  of  these 
foldings  the  extent  of  the  mucous  membrane  is  greatly  increased 
over  what  it  would  be  did  it  simply  line  the  intestine. 

Vilii. — Projecting  from  the   mucous  membrane  including  the 


STRUCTURE  OF  THE  SMALL  INTESTINE. 


223 


valvulse  conniventes  are  the  mill  (Fig.  117),  which  are  so  numerous 
as  to  give  to  it  a  velvety  appearance.  Between  them  open  the 
glands  of  Lieberkiihn.  The  villi  are  prominences,  some  triangular, 
some  conical,  and  some  filiform  in  shape,  and  in  length  are  about 
0.5  to  0.7  mm.,  and  in  width  at  their  base  about  one-fourth  their 
length  (Fig.  118).  They  are  most  numerous  in  the  duodenum  and 
the  jejunum,  although  present  throughout  the  whole  extent  of  the 


Epithelium 
of  villus. 


Epithelium 
of  villus. 


Goblet-cell. 


Gland  (crypt) 
of  Lieber- 
kiihn. 


—   Mucosa. 


Muscularis 
mucosae. 


FIG.  118. — Section  through  mucous  membrane  of  human  small  intestine  ;  X88:  at 
a  is  a  collapsed  chyle-vessel  in  the  axis  of  the  villus  (Bohm  and  Davidoff ). 

small  intestine.     It  has  been  estimated  that  there  are  no  less  than 
4,000,000  of  these  villi  in  an  intestine. 

Each  villus  is  composed  of  retiform  tissue,  and  is  covered  with 
a  single  layer  of  columnar  epithelium  resting  upon  a  basement- 
membrane  consisting  of  a  layer  of  endothelial  cells.  Between  the 
cells  of  columnar  epithelium,  at  their  bases  and  in  the  retiform 
tissue,  are  numerous  lymph-corpuscles.  Between  adjoining  epithe- 
lial cells  and  also  between  the  endothelial  cells  is  interstitial 


224 


INTESTINAL  DIGESTION. 


cement-substance,  and  the  reticulum  of  the  matrix  of  the  villus  is 
continuous  from  the  interior  of  the  villus  through  this  interstitial 
substance  to  its  exterior.  Next  the  basement-membrane  is  a 
plexus  of  capillary  blood-vessels.  Still  more  interior  is  muscular 
tissue,  a  part  of  the  muscularis  mucosae,  while  the  central  structure 
of  all  is  a  lacteal. 

The  capillary  plexus,  muscular  tissue,  and  lacteal  are  sur- 
rounded by  reticular  tissue  constituting  the  matrix  of  the  villus, 
and  in  the  interstices  of  this  are  lymph-corpuscles  and  the  cells  of 


FiG.  119. — Longitudinal  section  through  summit  of  villus  from  human  small 
intestine  ;  X  900  (Flemming's  solution) :  at  a  is  the  tissue  of  the  villus  axis ;  &, 
epithelial  cells;  c,  goblet-cell;  d,  cuticular  zone  (Bohm  and  Davidoff). 

the  villus  ;  large,  flat  cells  with  oval  nuclei.  If  the  components  of 
a  villus  are  named  in  the  reverse  order  to  that  just  given,  we  shall 
have,  starting  from  the  center,  (1)  lacteal,  (2)  muscular  tissue, 
(3)  capillary  plexus,  (4)  basement-membrane,  (5)  columnar  epi- 
thelium. The  lacteals  are  single  in  some  of  the  villi  and  in  others 
double.  Their  walls  consist  of  a  single  layer  of  endothelium,  and 
the  cement-substance  between  the  cells  is  continuous  with  the 
reticular  tissue  composing  the  matrix.  It  will  be  seen,  therefore, 
that  from  the  lacteal  to  the  surface  of  the  villus  there  is  continuous 
reticular  tissue.  This  is  regarded  by  Dr.  Watney  as  the  path 


STRUCTURE  OF  THE  SMALL  INTESTINE. 


225 


which  the  particles  of  fat  take  when  they  are  undergoing  the 
process  of  absorption  (p.  261) — i.  e.,  from  the  lumen  of  the  in- 
testine (1)  through  the  interstitial  or  cement-substance  of  the 
columnar  epithelium ;  (2)  through  the  same  substance  in  the 
basement-membrane;  (3)  through  the  reticulum  of  the  matrix; 
(4)  through  the  interstitial  substance  of  the  lacteals  into  the  inte- 
rior of  this  structure. 

The  lacteals  are  the  lymphatic  vessels  of  the  small  intestine, 


~|Er» Central 

chyle-vessel 
of  villus. 


hyle-vesseL 


-Mucosa. 
Muscularis 
mucosse. 

S — Submucosa. 

Plexus  of 
"    lymph-ves- 
sels. 

Circular  mus- 
~    cular  layer. 
^^    Plexus  of 

Sc?—    Ivmph-ves- 

— -•     .   .  orr-fT^T  ~  ~~  °f*r~*'  . —  ,  •>„•=• 'TVT^T^  -*L".~T'  l  -  ^-»"~v         ct»lc 

&%ffi#2^^ 

'  '•"*'    •••"•- 1 — s ' « — • -=— - —       layer  with 

Vein.  serous  coat. 

FIG.  120. — Schematic  transverse  section  of  the  human  small  intestine  (after  F.  P. 

Mall). 

which,  on  leaving  the  villi,  form  a  plexus  in  the  mucous  and  sub- 
mucous  tissue,  and  discharge  into  larger  lymphatic  vessels,  and 
theii  contents  finally  pass  into  the  thoracic  duct. 

Brunner's  Glands  (Fig.  121). — In  the  submucous  coat  of  the 
upper  part  of  the  duodenum,  and  to  a  less  extent  in  that  of  the 
lower  part,  and  in  the  beginning  of  the  jejunum,  are  certain  glands 
known  as  the  glands  of  Brunner,  or  the  duodenal  glands.  These 
are  tubulo-racemose  glands,  similar  to  the  lobules  of  a  salivary 
gland.  They  discharge  through  ducts  which  open  upon  the  sur- 

15 


226 


INTESTINAL  DIGESTION. 


face  of  the  mucous  membrane  of  the  intestine.  Their  secretion 
is  mucus  having  a  slightly  alkaline  reaction,  but  it  has  never  been 
successfully  obtained  so  pure  as  to  admit  of  its  being  analyzed. 
These  glands  are  so  few  in  number,  comparatively,  that  their  prod- 
uct cannot  be  very  abundant  nor  very 
important  in  its  action  upon  the  food, 
although  an  enzyme  has  been  described 
as  one  of  its  constituents  which  has 
the  power  of  converting  maltose  into 
glucose.  The  secretion  of  the  glands, 
together  with  that  of  the  follicles  of 
Lieberklihn,  constitutes  the  intestinal 
juice.  These  glands  are  inflamed  and 
ulcerate  whenever  the  body  is  burned 
to  any  great  extent. 

Follicles  of  Lieberkuhn. — The  folli- 
cles or  crypts  of  Lieberkuhn,  which 
are  found  throughout  the  entire  length 
of  the  small  intestine,  are  simple  tubu- 
lar glands  in  the  mucous  membrane, 
and  not  beneath  it,  as  is  the  case  with 
the  glands  of  Brunner.  They  are 
lined  with  a  layer  of  columnar  epithe- 
lium similar  to  that  which  covers  the 
surface  of  the  mucous  membrane  and 
the  villi  (Fig.  122). 

Solitary  and  Anminated  Glands. — 
The  solitary  glands  are  found  in  the 
mucous  membrane  of  the  whole  small 
intestine,  in  greater  number,  however, 
in  the  lower  part  of  the  ileum.  They 
have  a  diameter  of  from  3  to  6  mm., 
and  present  a  round  and  somewhat 
prominent  appearance.  They  are 
composed  of  lymphoid  tissue,  and  contain  many  lymph-corpuscles. 
They  have  no  duct,  and  their  product  probably  oozes  through 
the  walls  of  the  glands  and  contributes  something  to  the  in- 
testinal juice.  When  these  glands  are  aggregated  they  form 
patches,  and  are  called  agminated  glands  or  Peyer's  patches 
(Fig.  123). 

These  are  about  twenty-five  in  number,  though  in  youth  as 
many  as  forty-five  have  been  seen,  while  in  old  age  they  are  absent. 
They  occur  principally  in  the  ileum,  though  they  are  also  found  in 
the  lower  part  of  the  jejunum,  where  they  are  much  smaller  and 
circular,  and  sometimes  in  the  lower  part  of  the  duodenum.  These 
patches  vary  in  length  from  1.5  cm.  to  10  cm.,  and  in  width 
from  4  cm.  to  5  cm.  Like  the  solitary  glands,  they  are  with- 


FIQ.  121.— Vertical  section  of 
duodenum,  showing  villi  (a) ; 
crypts  of  Lieberkuhn  (b),  and 
Brunner's  glands  (c)  in  the  sub- 
mucosa  (s),  with  ducts  (d)  ;  mus- 
cularis  mucosse  (m),  and  circular 
muscular  coat  (/)  (Schofield). 


STRUCTURE  OF  THE  LARGE  INTESTINE. 


227 


out  ducts,  and  their  secretion  finds  an  exit  in  the  same  manner. 
In  typhoid  fever  they  become  inflamed  and  often  undergo  ulcera- 
tion. 

Structure  of  the  I/arge  Intestine. — The  coats  of  this 
portion  of  the  alimentary  canal  are  the  same  in  number  and  kind 
as  those  of  the  small  intestine,  although  the  arrangement  of  the 
longitudinal  fibers  of  the  muscular  coat  is  in  some  portions  in  the 


Intestinal  epithe- 
lium. 


Lumen  of  gland. 
Goblet-cell. 


Mucosa. 


Mucosa. 


—  Muscularis 
mucosae. 

FIG.  122. — From  colon  of  man,  showing  glands  of  Lieberkiilm ;  X  200  (Bohm  and 

Davidoff). 

form  of  bands,  a  quite  different  arrangement  from  that  in  the 
small  intestine.  At  the  anus  the  circular  fibers  constitute  the 
internal  sphincter. 

The  mucous  membrane  contains  both  solitary  glands  (Fig. 
117)  and  glands  which  resemble  the  follicles  of  Lieberkiilm,  and 
indeed  are  called  by  that  name  by  some  writers  (Fig.  122);  still 
the  secretion  differs  very  materially,  not  containing  any  enzymes 


228 


INTESTINAL    DIGESTION. 


possessing  digestive  powers.  The  epithelium  contains  mucus- 
secreting  or  goblet-cells,  and  their  product  is  principally  mucus. 

Succus  Entericus  or  Intestinal  Juice. — This  is  the  secre- 
tion of  all  the  glands  of  the  small  intestine ;  but  the  follicles  of 
Lieberkiihn,  being  vastly  more  numerous  than  the  others,  con- 
tribute by  far  the  greater  part  of  the  fluid.  It  is  obtained  from 
animals  by  making  a  "  Thiry-Vella  fistula."  This  consists  in 
cutting  out  a  piece  of  intestine,  from  10  to  30  cm.  long,  without 
interfering  with  its  nerves  or  blood-supply,  and  sewing  the  open 
ends  to  two  openings  in  the  abdominal  wall.  The  severed  ends 
of  the  intestine,  from  which  the  piece  has  been  isolated,  are  also 

sewn  together.  The  fluid  ob- 
tained from  the  portion  thus  iso- 
lated is  pure  intestinal  juice,  with- 
out admixture  with  food  or  other 
substances.  This  operation  has 
been  performed  on  the  dog,  and 
the  juice  obtained  is  described  as 
being  limpid,  yellowish,  having  a 
specific  gravity  of  1010,  and  a 
strongly  alkaline  reaction,  due  to 
the  presence  of  sodium  carbonate. 
The  fluid  has  also  been  ob- 
tained from  a  human  being,  from 
a  piece  of  intestine  9  cm.  long, 
situated  about  20  cm.  above  the 
ileocecal  valve.  The  daily  prod- 
uct averaged  27  c.c.  The  spe- 
cific gravity  averaged  about  1007. 
The  fluid  was  opalescent  and  often 

of  a  brownish  color.  It  was  always  alkaline,  and  when  treated 
with  acids  carbonic  acid  gas  was  evolved.  It  gave  all  the  proteid 
reactions,  but  did  not  reduce  Fehling's  solution  or  change  the 
color  of  a  solution  of  iodine. 

Action  of  Intestinal  Juice. — Although  the  chemical  composition 
of  this  fluid  is  not  well  understood,  it  is,  nevertheless,  known  to 
possess  several  enzymes  :  amylolytic,  sugar-splitting,  and  activating 
(p.  119).  The  amylolytic  enzyme  changes  starch  to  maltose,  and 
possibly  some  dextrose.  It  has  been  claimed  that  the  maltose  is 
converted  into  glucose  by  the  product  of  Peyer's  patches.  Another 
enzyme,  invertin  or  invertase,  changes  saccharose  into  dextrose  and 
levulose.  The  changes  undergone  in  this  process  have  been 
already  described  (p.  93).  The  succus  entericus  contains  no  pro- 
teolytic  enzyme,  nor  is  fat  split  up  by  it.  Its  alkalinity  aids  in 
the  em  unification  of  fats.  The  activating  enzyme  is  enterokinase, 
which  changes  trypsinogen  into  trypsin. 


FIG.  123. — Mucous  membrane  of  the 
jejunum  (Testut) :  1,  Peyer's  patch; 
2.  its  border ;  3,  solitary  follicles ;  4,  4, 
valvulse  conniventes. 


STRUCTURE  OF  THE  PANCREAS. 


229 


From  the  above  considerations  the  intestinal  juice  must  be 
regarded  as  possessing  some  digestive  action  upon  the  food-stuffs, 
its  most  marked  property  being  its  power  of  inversion.  Ti  : 


It  is 


Epithelium 
of  intes- 
tine. 


Gland.— ^ 


Submu- 
cosa. 


FIG.  124. — A  solitary  lymph-nodule  from  the  human  colon  :  at  a  is  seen  the  pro- 
nounced concentric  arrangement  of  the  lymph-cells  (Bohm  and  Davidoff). 

not  an  abundant  secretion,  and  one  of  its  important  offices  is, 
doubtless,  to  lubricate  the  mucous  membrane  of  the  small  in- 
testine. 

THE  PANCREAS, 

Structure  of  the  Pancreas. — This  organ  is  a  gland  of  the 
tubulo-racemose  type,  and,  from  its  resemblance  to  the  salivary 
glands,  is  described  as  the  abdominal  salivary  gland ;  the  pancre- 
atic alveoli  are,  however,  longer  and  more  tubular.  Its  location 
is  in  the  abdominal  cavity,  behind  the  stomach  and  between  the 
duodenum  and  the  spleen.  Its  length  is  from  15  to  23  cm.,  its 
width  about  4.5  cm.,  and  its  thickness  2.8  cm.  The  alveoli  are 
lined  with  columnar  or  polyhedral  cells,  which,  in  the  fresh  con- 
dition, contain  small  granules  in  the  protoplasm  of  their  inner 
two-thirds,  while  that  of  the  outer  third  is  clear.  This  clear 
portion  becomes  larger,  encroaching  upon  the  granular  part,  when 
the  gland  is  active. 

The  changes  which  these  cells  undergo  may  be  more  distinctly 
shown  by  means  of  carmine,  which  acts  as  a  staining  agent.  Thus 
Fig.  125  represents  the  appearance  of  the  cells  of  a -pancreas 
which  was  removed  from  a  dog  that  had  fasted  for  twenty-four 
hours. 


230 


THE  PANCREAS. 


The  gland  was  hardened  in  alcohol  and  a  section  of  it  was 
stained  with  carmine.  The  clear  portion  at  the  base  of  the  cells 
takes  the  stain  better  than  the  more  granular,  internal  portion.  Fig. 


FIG.  125. — Pancreas  of  dog  during  hunger;  preserved  in  alcohol  and  stained  in 
carmine  (after  Heidenhain). 

126  represents  a  section  from  a  dog  that  had  been  fed  from  six  to 
ten  hours  before  the  gland  was  removed ;  the  encroachment  of  the 
clear  upon  the  granular  portion  is  shown  by  the  greater  width  of 


FlQ.  126.— Pancreas  of  dog  during  first  stage  of  digestion ;  alcohol,  carmine  (after 

Heidenhain). 

the  stained  zone.  In  other  words,  the  granules  are  being  used  up 
to  form  these  products,  the  enzymes.  Fig.  128  represents  the 
cells  when  they  have  returned  to  a  condition  of  rest. 


STRUCTURE  OF  THE  PANCREAS. 


231 


FIG.  127.— Pancreas  of  dog  during  second  stage  of  digestion;  alcohol,  carmine 

(after  Heidenhain). 

In  the  connective  tissue  are  groups  or  islets  of  epithelium-like 
cells  (Figs.  129,  130),  which  are  supposed  to  produce  the  internal 
secretion  of  the  pancreas  (p.  239). 


Outer  zone  of  — ^ 
a  secretory 
cell. 


Connective— 
tissue. 


Larger  gland- 
duct. 


— Centro-acinal 
cell. 


ntro-acinal 
cell. 


—  Intermediate 

tubule. 

Inner  granu- 
lar zone  of 
secretory 
cells. 


FIG.  128. — From  section  through  human  pancreas;  X  450  (sublimate)  (Bohm  and 

Davidoff). 


232 


THE  PANCREAS. 


Pancreatic  Juice.— The  most  important  changes  which  the 
food  undergoes  in  the  process  of  intestinal  digestion  are  those 
which  are  due  to  the  action  of  the  pancreatic  juice.  This  is  the 


Alveolus. 


Intermedi- 
ary duct. 


Centro-acinal    — - 
cell. 


Intermediary  - 
duct. 


Intralobular    - 
duct. 


FIG.  129.— From  section  through  human  pancreas :  X  about  200  (sublimate)  (Bohm 

and  Davidoff). 

product  of  the  pancreas,  and  reaches  the  intestine  by  means  of 
the  pancreatic  duct  which,  together  with  the  common  bile-duct, 
opens  into  the  duodenum  about  8  to  10  cm.  below  the  pylorus. 


Connective 
tissue. 

Centro-acinal 
cell. 

Secretory  cell. 


Intermediate 
duct. 


FlG.  130. — Scheme  showing  relation  of  three  adjoining  alveoli  to  excretory  duct, 
illustrating  origin  of  centro-acinal  cells  (Bohm  and  Davidoff). 

Quantity  of  Pancreatic  Juice. — The  amount  of  this  fluid  secreted 
daily  in  the  human  being  is  not  known,  but  it  has  been  found  that 
in  the  dog  it  is  2.5  grams  per  kilo  of  body-weight.  This  would 
give  in  a  man  weighing  70  kilos,  175  grams  daily. 


PANCREATIC  JUICE. 


233 


Composition  of  Pancreatic  Juice. — The  pancreatic  juice  has  been 
obtained  repeatedly  from  the  dog  and  the  rabbit  by  the  operation 
of  establishing  a  permanent  pancreatic  fistula.  For  this  purpose 
that  portion  of  the  duodenum  of  a  rabbit  into  which  the  main 
duct  discharges,  which  in  this  animal  is  about  35  cm.  below  the 


FIG.  131. — Stomach  in  place  after  removal  of  liver  and  mass  of  intestines:  A, 
diaphragm;  B,  B',  thoraco-abdominal  wall;  C,  right  kidney  with  c,  its  ureter; 
D,  right  suprarenal  capsule  ;  E,  left  kidney  with  e,  its  ureter  ;  F. ,  spleen ;  G,  apon- 
euroses  of  transversales :  H,  H',  quadrati  lumborum ;  /,  /',  psoas  muscles;  K,  esoph- 
agus ;  /,,  stomach  ;  M,  duodenum.  1,  cardia  ;  2,  greater  curvature ;  3,  lesser  curvature  ; 
4,  great  tuberosity  or  fundus;  5,  small  tuberosity  or  antrum  of  pylorus  ;  6,  pylorus; 
7,  right  vagus  ;  left  vagus ;  9,  thoracic  aorta  ;  9',  abdominal  aorta ;  10,  inferior  dia- 
phragmatic arteries;  11,  celiac  axis;  12,  hepatic  artery;  13,  right  gastro-epiploic ; 
14,  coronary  artery  ;  15,  splenic  artery ;  16,  16',  superior  mesenteric  artery  and  vein  ; 
17,  inferior  mesenteric  artery;  18,  spermatic  artery;  19,  gall-bladder;  20,  cystic 
duct;  21,  hepatic  duct;  22,  inferior  vena  cava ;  23,  portal  vein;  24,  great  sympa- 
thetic (Testut). 

opening  of  the  bile-duct,  is  opened  and  a  glass  cannula  is  intro- 
duced into  the  duct  and  the  secretion  collected  as  it  escapes.  The 
amount  thus  obtained  from  rabbits  is  very  small ;  it  is  clear,  color- 
less, alkaline,  and  does  not  clot.  That  obtained  from  fistulse  in 
dogs  is  thicker,  and  coagulates  on  standing,  although  it  is  less  thick 
after  the  h'stulse  have  existed  for  some  time.  The  specific  gravity, 


234 


THE  PANCREAS. 


FIG.  132. — Excretory  ducts  of  the  pancreas:  A,  pancreas,  with  a,  its  head;  B, 
duodenum;  C,  jejunum;  D,  gall-bladder.  1,  main  pancreatic  duct  of  Wirsung; 
2,  accessory  duct  with  2',  its  opening  upon  the  postero-internal  wall  of  the  duo- 
denum; 3,  ampulla  of  Vater;  4,  common  bile-duct;  5,  cystic  duct;  6,  hepatic  duct; 
7,  aorta ;  8,  superior  mesenteric  vessels  ;  9,  celiac  axis  with  its  three  branches(Testut). 

too,  falls  from  1030  to  1010.     The  following  table  gives  its  com- 
position : 

Pancreatic  Juice  of  Dog  (C.  Schmidt). 


CONSTITUENTS. 

Immediately  after 
establishing  fistula. 

From  permanent 
fistula. 

Water  

900.76 

980.45 

Solids    

99.24 

19.55 

Organic  substances 

90  44 

12  71 

Ash  ...            ... 

8.80 

6  84 

Sodium  carbonate  ...            ... 

0.58 

3  31 

Sodium  chlorid  
Calcium,  magnesium,  and  sodium  phos- 
phates 

7.35 
0  53 

2.50 
0  08 

Less  is  known  as  to  the  chemical  composition  of  human  pancre- 
atic juice.  Herter  obtained  the  fluid  from  an  enlarged  duct  caused 
by  carcinoma  of  the  duodenum.  In  1000  parts  of  this  there  were 
24.1  parts  of  total  solids,  17.8  parts  of  organic  matter,  and  6.2 
parts  of  ash.  Zadawsky  obtained  the  juice  from  a  young  woman 


PANCREATIC  JUICE.  235 

from  whom  a  tumor  of  the  pancreas  had   been   removed.     The 
analysis  of  this  was  as  follows : 

Water 864.05 

Proteids 92.05 

Other  organic  substances 40.46 

Salts 3.44 

Enzymes  of  Pancreatic  Juice. — It  is  a  remarkable  fact  that  the 
pancreatic  juice  of  all  vertebrates,  so  far  as  examined,  contains 
four  enzymes  :  (1)  amylolytic,  (2)  proteolytic,  (3)  fat-splitting,  and 
(4)  milk-curdling. 

Amylopsin. — This  is  the  amylolytic  enzyme  of  the  pancreatic 
juice,  and  is  regarded  as  identical  with  ptyalih  of  the  saliva, 
although  pancreatic  juice  has  much  greater  amylolytic  power  than 
saliva,  and  acts  upon  uncooked  starch  ;  but  whether  this  is  due  to 
a  difference  in  the  enzymes  or  because  in  pancreatic  juice  the 
enzyme  is  more  concentrated,  has  not  been  determined.  Some 
authorities  include  them  both  under  the  name  of  ptyalin. 

Amylopsin  appears  in  the  pancreatic  juice  for  the  first  time 
about  one  month  after  birth,  while  ptyalin  is  present  in  the  human 
parotid  gland  at  birth,  but  in  the  submaxillary  gland  not  until 
about  two  months  subsequently. 

The  optimum  temperature  for  amylopsin  is  from  30°  C.  to 
45°  C.,  while  between  60°  C.  and  70°  C.  it  is  destroyed.  Its 
activity  is  greatest  when  the  reaction  is  neutral  or  when  a  minute 
trace  of  acid  is  present,  such  as,  for  instance,  0.01  per  .cent,  of 
hydrochloric  acid.  Its  action  on  starch  is  to  change  it  to  maltose 
and  dextrose,  or,  under  some  circumstances,  to  maltose  alone. 
Authorities  who  regard  the  action  of  saliva  upon  starch  as  being 
of  comparatively  little  importance  look  to  amylopsin  and  to  the 
amylolytic  enzyme  of  the  intestinal  juice  as  the  principal  agents 
in  starch  conversion.  This  we  regard  as  a  mistake,  and  are  in- 
clined to  place  a  much  higher  value  upon  salivary  digestion  than 
do  these,  but  at  the  same  time  would  give  pre-eminence  to  the 
pancreatic  juice  as  a  starch  converter. 

Trypsin. — This  is  the  proteolytic  enzyme  of  the  pancreatic  juice, 
and  its  power  in  this  regard  is  greater  than  that  of  pepsin.  It 
has  been  found  in  the  pancreatic  juice  during  the  last  third  of  fetal 
life.  Its  activity  is  greatest  when  sodium  carbonate  is  present  to 
the  amount  of  about  1  per  cent.,  although  it  acts  when  the  reac- 
tion is  neutral  or  very  slightly  acid.  When  hydrochloric  acid 
is  present  to  any  considerable  extent  the  enzyme  is  destroyed,  and 
this  is  hastened  when  pepsin  is  also  present. 

Trypsin  has  never  been  isolated,  so  that  its  chemical  com- 
position has  not  as  yet  been  determined.  In  the  action  of  the 
cells  of  the  pancreas,  the  zymogen  trypsinogen  is  first  formed, 
and  this  later  becomes  trypsin.  In  studying  its  action,  a  pancreas 


236  THE  PANCREAS. 

may  be  cut  up  finely  and  the  enzyme  extracted  with  glycerin,  to 
which  extract  a  solution  of  sodium  carbonate  of  from  0.2  to  0.5 
per  cent,  is  added.  Inasmuch  as  the  pancreas  and  its  extracts 
undergo  putrefaction  very  readily,  the  glycerin  preparation  may 
be  preserved  by  the  addition  of  a  few  drops  of  an  alcoholic 
solution  of  thymol. 

Tryptic  Digestion. — The  differences  between  peptic  and  tryptic 
digestion  are  quite  marked.  Pepsin  requires  an  acid  medium ; 
trypsin  acts  best  in  one  that  is  alkaline.  When  peptic  digestion  of 
a  solid  proteid  occurs,  this  first  swells  up  and  then  gradually  dis- 
solves, while  in  tryptic  digestion  there  is  no  preliminary  swelling 
of  the  proteid,  but  the  erosion  begins  at  once.  In  peptic  diges- 
tion the  proteid  first  becomes  acid-albumin,  then  passes  into 
the  stage  of  primary  proteoses,  followed  by  that  of  secondary 
proteoses,  and  finally  becomes  peptones.  In  tryptic  digestion 
it  passes  at  once  into  the  stage  of  secondary  proteoses,  and  then 
on  into  peptones.  These  peptones  are  spoken  of  as  ampho- 
peptones,  because  there  are  at  least  two  of  them,  anti-peptone  and 
hemi-peptone.  The  action  of  pepsin  stops  when  these  are 
formed,  but  trypsin  can  act  still  further  by  splitting  up  the  hemi- 
peptone  into  a  number  of  substances,  among  them  leucin,  tyrosin, 
aspartic  acid,  tryptophan,  and  lysatinin.  What  office  these  sub- 
stances have  in  the  body,  if  any,  is  as  yet  undetermined,  though 
it  is  probable  that  a  portion  of  the  urea  found  in  the  body  is 
derived  from  lysatinin,  and  Halliburton  states  that  "  recent  research 
indicates  that  even  the  simple  cleavage  products  (leucin,  tyrosin, 
etc.)  may  also  be  utilized  for  the  synthetic  production  of  proteids. 

The  changes  which  proteids  undergo  in  tryptic  digestion  are 
well  shown  in  the  following  scheme  of  Neumeister : 

Proteid. 

Deutero-albumoses  (proteoses). 

Ampho-peptones. 


.1  .  ! 

Anti-peptone.         Hemi-peptone, 


I.I.  I  I 

Leucin.     Tyrosin.     Aspartic  Acid.     Tryptophan.     Lysatinin. 

Steapsin. — The  fat-splitting  or  lipolytic  enzyme  of  the  pancre- 
atic juice,  steapsin,  is  sometimes  termed  pialyn.  Its  action  has 
already  been  described  in  connection  with  saponification  (p.  100), 
and  consists  in  the  taking  up  of  water  by  the  neutral  fats,  which 
then  "  split  up,"  glycerin  and  a  free  fatty  acid  being  the  result. 


PANCREATIC  JUICE.  237 

The  evidence  that  the  pancreatic  juice  has  this  power  is  unques- 
tioned, and  that  it  is  due  to  the  presence  of  an  enzyme  is  proved 
by  the  fact  that  boiling  destroys  this  power,  and  by  the  further 
fact  that  it  cannot  be  due  to  bacteria,  for  antiseptics  do  not  affect 
it ;  nevertheless,  the  knowledge  as  to  its  properties  is  very  meager. 
Its  action  upon  fats  is  very  rapid,  and  it  is  probable  that  "  it  is 
capable  of  splitting  up  all  the  fat  of  a  full  meal  in  the  ordinary 
time  of  digestion  within  the  body."  The  presence  of  bile,  ^  by 
virtue  of  its  contained  bile-salts  or  bile-acids,  increases  its  activity, 
and  this  is  still  greater  when  hydrochloric  acid  is  present. 

An  interesting  fact  in  connection  with  the  secretion  of  the  pan- 
creatic juice  is  that  its  composition  varies  according  to  the  nature 
of  the  food  ingested.  Thus,  if  fat  is  present  in  considerable  quan- 
tity, there  will  be  produced  a  corresponding  amount  of  the  lipolytic 
enzyme,  whereas  if  the  diet  consists  largely  of  muscular  tissue, 
trypsin  will  preponderate.  There  is  no  reason  to  believe  that  this 
variation  in  the  composition  of  digestive  juices  is  confined  to  the 
pancreas  ;  it  is  doubtless  equally  true  of  other  digestive  organs  that 
their  products  vary  with  the  character  of  the  food. 

Emulsifying  Power  of  Pancreatic  Juice. — One  of  the  offices 
performed  by  the  pancreatic  juice  is  to  make  an  emulsion  of  fats 
which  form  an  important  part  of  the  food.  This  action  is  not 
due  to  any  enzyme,  but  to  the  formation  of  fatty  acids  by  the 
steapsin  ;  indeed,  this  is  regarded  by  some  authorities  as  the  chief 
office  of  the  lipolytic  enzyme.  The  splitting,  up  of  fat  is  in  and 
of  itself,  according  to  this  theory,  of  no  great  physiologic  impor- 
tance, inasmuch  as  only  a  part  of  the  fat  is  thus  split  up,  but  the 
fatty  acids  which  result,  together  with  the  fatty  acids  which  the  fats 
themselves  contain,  bring  about  the  emulsification  of  the  main  por- 
tion of  the  fat,  which  process  is,  according  to  some  authorities,  so 
essential  in  preparing  it  for  absorption.  Of  the  theories  propounded 
to  explain  fat  absorption,  we  shall  speak  later  (p.  261). 

The  fatty  acids  resulting  from  the  decomposition  of  the  fat  unite 
with  the  alkaline  salts  in  the  small  intestine,  probably  those  of 
the  bile  and  the  intestinal  juice  rather  than  those  of  the  pancreatic 
juice,  and  form  soaps,  which,  aided  by  the  peristaltic  movements 
of  the  intestine,  convert  the  fat  into  an  emulsion.  The  proteids 
of  the  pancreatic  juice  take  no  part  in  this  emulsifying  process, 
but  it  is  very  materially  aided  by  the  presence  of  the  bile,  inas- 
much as  bile  and  pancreatic  juice  acting  together  split  up  fat  much 
more  quickly  than  the  juice  alone. 

In  what  manner  soaps  act  to  emulsify  fats  is  not  known.  Some 
have  supposed  that  the  soap  forms  a  film  around  the  fat-globules 
after  they  have  been  finely  divided,  which  prevents  their  uniting ; 
but  the  formation  of  such  a  film  has  never  been  demonstrated. 
Moore,  in  Schafer's  Physiology,  says  that  the  very  fine  subdivision 
of  the  fat  and  the  increased  viscosity  of  the  menstruum  occasioned 


238 


THE  PANCREAS. 


by  the  dissolved  soap,  are  quite  sufficient  to  explain  the  per- 
manency of  emulsions  of  fat. 

Milk-curdling  Enzyme  of  the  Pancreatic  Juice. — Milk,  to  which 
an  extract  of  the  pancreas  has  been  added,  coagulates,  and  the 
term  pancreatic  casein  lias  been  applied  to  this  precipitate.  It  is 
probably  a  substance  intermediate  between  casein  and  caseinogen. 
The  coagulating  agent  is  considered  to  be  an  enzyme,  though 
nothing  definite  is  known  about  it. 

Innervation  of  the  Pancreas. — The  nerves  which  supply 
this  organ  are  from  the  celiac  plexus  of  the  sympathetic,  together 
with  some  fibers  from  the  right  vagus,  and  are  non-medullated 
and  gangliated.  When  food  enters  the  stomach  of  a  dog,  almost 
immediately  the  secretion  of  pancreatic  juice  begins,  and  is  at 
a  maximum  in  from  one  to  three  hours.  It  then  diminishes  until 
about  five  or  six  hours  after  the  meal  is  taken,  when  it  again 
increases  until  the  ninth  or  eleventh  hour,  and  again  diminishes 
until  the  sixteenth  or  seventeenth  hour,  when  it  is  practically  niL 
Fig.  133  shows  this  in  the  dog.  Just  what  the  facts  are  in  man 
is  unknown,  although  it  is  believed  that  the  secretion  begins  about 
the  time  of  entrance  of  food  into  the  stomach ;  but  its  increase  and 


13 

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15     16     //     18 


FIG.  133.— Curve  of  the  secretion  of  pancreatic  juice  during  digestion.  The 
figures  along  the  abscissa  represent  hours  after  the  beginning  of  digestion :  the 
figures  along  the  ordinate  represent  the  quantity  of  this  secretion  in  cubic  centi- 
meters. Curves  of  two  experiments  are  given  (after  Heideuhain). 

diminution  would,  doubtless,  vary  very  materially  from  those  of 
the  dog,  which  was  fed  but  once  during  the  day. 


THE  LIVER.  239 

Formerly  it  was  considered  that  the  secretion  of  pancreatic  juice 
is  a  reflex  act  brought  about  by  stimulation  of  the  afferent  fibers 
of  the  mucous  membrane  of  the  stomach  or  intestine,  or  both,  by 
the  gastric  juice,  but,  according  to  Bayliss  and  Sterling,  it  is  due 
to  the  production  by  the  duodenal  glands,  as  a  result  of  the  action 
of  the  gastric  juice,  of  a  substance  termed  by  them  secretin,  which 
is  taken  up  by  the  blood  and,  being  carried  to  the  pancreas,  stimu- 
lates that  gland  to  the  secretion  of  the  pancreatic  juice. 

Fleig  claims  that  the  soaps  formed  in  the  small  intestine  as  a 
result  of  the  saponification  of  the  fats  of  the  food,  produce  by  their 
action  on  the  mucous  membrane  sapokrinin,  which  is  absorbed  and 
carried  to  the  pancreas  by  the  blood,  where  it  stimulates  that  gland, 
thus  aiding  in  the  secretion  of  pancreatic  juice. 

Internal  Secretion  of  the  Pancreas. — This  organ  has 
been  removed  from  animals  without  producing  an  immediately 
fatal  result,  but  in  every  such  case  sugar  has  appeared  in  the 
urine,  producing  a  condition  denominated  glycosuria,  and  this,  too, 
when  no  carbohydrate  was  present  in  the  food.  The  urine  has 
also  been  increased  in  quantity,  thirst  and  hunger  have  been 
marked,  and  emaciation  and  muscular  weakness  have  set  in,  with 
death  resulting  in  one  or  two  weeks.  If  the  gland  is  not  entirely 
removed,  so  little  as  one-fourth  or  one-fifth  being  left,  glycosuria 
does  not  occur,  and,  what  is  still  more  remarkable  is,  that  after 
the  removal  of  the  gland,  if  a  portion  of  it  is  grafted  under  the 
skin,  or  if  the  ducts  are  closed  so  as  to  prevent  the  secretion  from 
entering  the  duodenum,  glycosuria  is  also  absent.  All  of  which 
goes  to  prove  thai  besides  the  pancreatic  juice,  which  may  be  re- 
garded as  the  external  secretion  of  the  pancreas,  it  also  produces 
an  internal  secretion  which,  taken  up  by  the  blood  or  lymph,  either 
aids  in  destroying  the  sugar  produced  by  the  liver  or  muscles,  or 
else  inhibits  the  glycogenic  function  of  these  organs.  The  cells 
which  are  believed  to  form  this  secretion  have  been  described  in 
connection  with  the  pancreas  (p.  231). 

THE  LIVER. 

This  organ  is  situated  in  the  abdominal  cavity,  and  is  as  large 
as  all  the  other  glands  of  the  body  taken  together.  Its  transverse 
diameter  is  28  cm.,  anteroposterior  diameter,  20  cm.,  and  vertical 
diameter,  6  cm.  (Fig.  134).  Its  blood-supply  is  from  the  portal 
vein  and  hepatic  artery,  while  its  nervous  supply  is  from  the  left 
vagus  and  celiac  plexus.  It  is  covered  by  the  peritoneum,  and 
beneath  this  is  the  fibrous  coat,  which,  at  the  transverse  fissure,  is 
continuous  with  Glisson's  capsule.  This  connective-tissue  envelope 
covers  the  hepatic  artery,  portal  vein,  and  hepatic  duct,  and  accom- 
panies them  through  passages  in  the  liver,  the  portal  canals. 

Chemical  Composition. — The  liver  during  life  is  alkaline, 


L/.v/ 


240 


THE  LIVER. 


but  after  death  becomes  acid,  owing  to  the  formation  of  sarcolactic 
acid. 

Its  percentage-analysis  is  as  follows  (von  Bibra) : 

Gelatin 3.37 

Extractives 2.40 

Fats    .  2.50 


Water 

Insoluble  tissues  .    .    . 
Proteids     ...... 

Inorganic  constituents 


76.17 
9.44 
2.40 
1.10 


Proteids. — These  are  a  globulin  (cell-globulin)  coagulating  at 
45°  to  50°  C. ;  another  globulin,  coagulating  at  70°  C.  ;  a  nucleo- 
proteid  coagulating  at  about  60°  C.,  which,  when  injected  into 
the  blood-vessels,  causes  coagulation  of  the  blood  ;  and  an  albumin. 


Gastric  sur- 
face. 
Tuber  papilla  re. 

Tuber  omentale. 


\          Non-peritoneal 

\        \  surface. 

X^ -•  -\      Imp.  supra-ren. 

-     ^      ;-HT i       i  nnTi-norit^ 


-^ 


(non-perit). 


r-— ~- ip  Imp.  supra-ren. 
5T~"T"  Impressio  renalis. 


-?-j~  Imp.  duodenalis. 
Impressio  celica. 


Impressio  pylorica. 
FIG.  134. — Posterior  and  inferior  surfaces  of  the  liver. 

Extractives. — These  are  urea,  uric  acid,  xanthin,  hypoxan- 
thin,  and  jecorin.  This  last  constituent  contains  phosphorus, 
and  has  the  following  formula  :  C105H186N5SP3O45.  It  resembles 
lecithin,  but,  unlike  that  substance,  reduces  Fehling's  solution.  It 
is  not  confined  to  the  liver,  but  is  also  found  in  the  spleen,  muscle, 
and  brain.  The  liver  also  contains  a  nuclein,  with  which  iron  is 
in  combination,  called  Zaleski's  hepatin  and  also  Schmiedeberg's  fer- 
ratin.  Iron  is  present  in  the. liver  of  young  animals  in  greater 
proportion  than  in.  old  ones,  and  it  is  stated  that  animals  are  born 
with  iron  in  both  liver  and  spleen.  This  iron  meets  the  demand 
of  the  body  until  the  use  of  milk  is  given  up,  this  fluid  being  poor 
in  iron. 

Structure. — The  liver  is  made  up  of  five  lobes,  which  are 
composed  of  lobules  each  having  a  diameter  of  about  1  mm.,  and 
these  in  turn  contain  hepatic  cells,  polyhedral  in  shape,  the  secret- 
ing elements  of  the  liver,  each  having  a  diameter  of  about  ^ 
mm.,  and  containing  a  nucleus.  The  protoplasm  contains  glycogen 
and  iron-containing  pigment-granules,  and  may  also  contain  fat. 
Nerve-fibers  are  described  by  some  histologists  as  terminating 
between  the  cells,  but  not  passing  into  their  interior.  The  lobules 
are  separated  by  connective  tissue,  which  is  abundant  in  the  pig, 
but  much  less  so  in  man. 


PORTAL   VEIS. 


241 


Hepatic  Artery. — The  hepatic  artery  is  a  branch  of  the 
celiac  axis,  and  enters  the  liver  at  the  transverse  fissure,  dividing 
here  into  two  branches,  right  and  left,  which  go  to  the  correspond- 
ing lobes.  This  artery  furnishes  nutrition  to  the  coats  of  the  large 
blood-vessels,  the  ducts,  the  membranes  of  the  liver,  and  to  Glis- 
son's  capsule.  It  also  gives  off  branches,  interlobular  branches, 
which  pass  between  the  lobules  and  give  off  lobular  branches. 
These  enter  the  lobules  and  end  in  a  capillary  network  between 
the  cells.  Whether,  however,  any  blood  is  carried  by  these 
vessels  directly  to  the  network  is  in  dispute. 

Portal  Vein. — This  vessel  also  enters  the  liver  at  the  trans- 
verse fissure,  dividing  into  two,  each  branch  going  to  the  corre- 
sponding lobe,  and  following  the  course  already  described  as  being 
taken  by  the  hepatic  artery  and  its  branches.  The  termination 


Portal  in-    _„_ 
terlobular 
branch, 
cut  longi- 
tudinally. 


The  same,  - 
cut  trans- 
versely. 


—Anasto- 
moses be- 
tween ves- 
sels of 
several 
lobules. 


FIG.  135. — Section  through  injected  liver  of  rabbit.     The  houndaries  of  the  lobules 
are  indistinct ;  X  about  35  (Bohrn  and  Davidoff). 

of  the  portal  vein  forms  the  interlobular  plexus,  which,  as  its  name 
implies,  is  in  the  connective  tissue,  between  the  lobules.  From 
this  go  off  vessels  which  run  to  the  center  of  the  lobule,  being 
connected  by  transverse  vessels,  the  whole  forming  a  capillary 
network,  in  the  meshes  of  which  are  the  hepatic  cells.  The  blood 
which  passes  through  this  network  is  discharged  at  the  center 
of  the  lobule  into  the  intralobular  or  central  vein,  which,  at  the 
base  of  the  lobule,  enters  the  sublobular  vein.  In  a  similar 

16 


242 


THE  LIVER. 


manner  all  the  intralobular  veins  discharge,  and  the  sublobular 
veins  unite  to  form  larger  veins,  which  terminate  in  the  hepatic 
veins,  which,  as  three  large  trunks  and  some  small  ones,  discharge 
into  the  vena  cava,  at  the  back  of  the  liver. 

Hepatic  Duct. — Between  adjoining  hepatic  cells  are  small 
passages,  intercellular  biliary  passages  or  bile-canaliculi,  which  are 
the  beginnings  of  the  hepatic  duct  (Fig.  137).  It  would  be  more 
correct  to  say  that  the  beginnings  of  the  hepatic  duct  are  within 
the  hepatic  cells  themselves,  for  it  has  been  demonstrated  that  in 
the  interior  of  these  cells  are  vacuoles  which  communicate  with 
the  bile-canaliculi  (Fig.  137).  The  canaliculi  pass  outward  to  the 
interlobular  spaces,  where  they  form  an  interlobular  biliary  plexus, 
from  which  ducts  are  given  off  that  enter  the  portal  canals,  and, 
covered  with  Glisson's  capsule,  in  company  with  the  branches  of 


Tntralobular 
vein. 

Branch  of 

portal  vein. 
Bile-duct. 

Branch  of 

hepatic 

artery. 
Interlobular 

connective 

tissue. 


FIG.  136.— Section  through  liver  of  pig,  showing  chains  of  liver-cells;  x  70  (Bohm 

and  Davidoff). 

the  portal  vein  and  hepatic  artery,  they  emerge  from  the  liver  at  the 
transverse  fissure  as  two  trunks,  right  and  left,  which  unite  to 
form  the  hepatic  duct.  This  is  from  3  to  5  cm.  in  length  and  has 
a  diameter  of  about  4  mm.  The  bile-canaliculi  have  no  wall 
save  such  as  is  made  by  the  hepatic  cells.  The  interlobular  ducts 
have  a  wall  of  connective  tissue  lined  with  columnar  epithelium. 
In  the  larger  duct  is  fibrous  and  plain  muscular  tissue.  The 
ducts  in  the  portal  canals  have  opening  into  them  cecal  diverticula, 
which  are  regarded  by  Sappey  as  mucous  glands. 

Gall-bladder.— The  gall-bladder  lies  on  the  under  surface 
of  the  liver  in  the  fossa  vesicalis,  being  attached  thereto  by  vessels 
and  connective  tissue.  The  neck  of  the  gall-bladder  terminates 
in  the  cystic  duct,  which  is  spiral  in  form,  and  unites  with  the 


GALL-BLADDER. 


243 


hepatic  duct  to  form  the  ductus  choledochus  or  common  bile-duct. 
The  cystic  duct,  from  the  neck  of  the  gall-bladder  to  its  union 
with  the  hepatic  duct,  is  3  to  7  cm.  long,  and  has  a  diameter  of 
2.3  mm.  The  length  of  the  common  bile-duct  depends  upon  the 
point  at  which  the  cystic  and  hepatic  ducts  unite,  which  is  not 


FIG.  137. — Diagram  of  a  segment  of  an  hepatic  lobule:  1,1,  interlobular 
portal  vein ;  2,  central  vein ;  3,  3,  intralobular  capillaries ;  4,  4,  interlobular 
hepatic  artery ;  5,  5,  ramifications  of  hepatic  artery,  contributing  to  the  formation 
of  the  intralobular  capillaries  :  6,  6,  interlobular  bile-duct;  7,  7,  its  ramifications  in 
the  lobule,  forming  a  plexus  of  intercellular  canaliculi ;  8,  8,  section  of  biliary  canal- 
iculi  with  their  intercellular  capillaries;  9.  9,  hepatic  cells;  10,  10,  interlobular 
lymphatics,  receiving  the  intralobular  lymphatics;  11,  11,  12,  intralobular  con- 
nective tissue  (Testut). 

uniform.  The  following  measurements  are  given  :  7  to  8  cm. 
(Sappey)  ;  2  to  4.5  cm.  (Luschka) ;  6  to  7  cm.  (Joessel).  Its 
diameter  is  from  5.6  mm.  to  7.5  mm. 

The  coats  of  the  gall-bladder  are  three  :  serous  or  peritoneal ; 
fbro-muscularj  made  up  of  fibrous  tissue  with  plain  muscular 
fibers  arranged  both  longitudinally  and  transversely,  the  former 
greatly  predominating ;  and  mucous.  This  last,  which  forms  the 


244  THE  LIVER. 

internal  coat,  presents  a  honey-comb  appearance.  It  is  covered 
with  columnar  epithelium.  The  mucous  membrane  of  the  cystic 
duct  forms  folds  which  bear  some  resemblance  to  the  valvulse 
conniventes  of  the  small  intestine.  These  folds  are  called  valvula 
Heisteri  or  the  valve  of  Heister.  The  mucous  membrane  is  con- 
tinuous with  that  lining  the  hepatic  and  common  bile-duct. 

Bile. — This  is  one  of  the  products  of  the  cells  of  the  liver ; 
as  it  is  secreted  it  passes  through  the  hepatic  and  cystic  ducts  into 
the  gall-bladder,  where  it  is  stored  until  needed  at  the  time  of 
intestinal  digestion,  when  it  is  discharged  through  the  common 
bile-duct  into  the  duodenum  by  an  opening  common  to  it  and  the 
pancreatic  duct. 

Properties  of  Bile. — The  bile  is  a  constant  secretion — i.  e.,  the 
liver-cells  are  constantly  producing  it,  although  it  leaves  the  liver 


FIG.  138. — View  of  duodenum  and  pancreas.  The  part  of  stomach  removed 
is  indicated  by  dotted  lines:  A,  quadrate  lobe:  B,  right  kidney;  C,  C",  right  and 
left  suprarenal  capsules;  D,  left  kidney;  E,  pancreas;  F,  upper  part  of  stomach; 
(?,  spleen;  H,  duodenum,  with  a,  b,  c,  d,  e.  its  five  parts;  /,  jejunum;  K,  duodeno- 
jejunal  angle.  1,  lower  end  of  esophagus;  2.  pyloric  orifice;  3,  celiac  axis;  4, 
coronary  artery;  5,  hepatic  artery;  6,  Spigelian  lobe  of  liver;  7,  7',  splenic  ves- 
sels; 8,  left  gastro-epiploic  artery;  9,  right  gastro-epiploic  artery;  10,  superior 
mesenteric  vessels;  11,  portal  vein;  12,  hepatic  duct;  13,  cystic  duct;  14,  gall- 
bladder; 15,  left  crus  of  diaphragm;  16.  aorta;  17,  vena  cava  inferior;  18.  inferior 
mesenteric  vessels;  19,  spermatic  vessels  (Testut). 

intermittently,  being  forced  out  by  the  contraction  of  the  muscular 
tissue  in  the  walls  of  the  bile-ducts.  Some  authorities  state  that 
it  flows  continuously  into  the  intestine.  But  whether  this  is  so 
or  not.  the  greater  part  is  stored  up  in  the  gall-bladder  during  the 


BILE.  245 

intervals  of  digestion,  to  be  expelled  therefrom  during  the  diges- 
tive process. 

When  the  bile  leaves  the  liver  it  is  a  clear  fluid  with  a  specific 
gravity  of  1010.  During  its  stay  in  the  gall-bladder  it  becomes 
viscid,  and  loses  some  of  its  water  and  inorganic  salts,  certainly 
some  of  the  chlorids,  which  are  absorbed  by  the  gall-bladder,  and 
its  specific  gravity  is  increased  to  1030  or  1040.  The  viscidity  in 
human  bile  is  due  to  mucin,  but  that  of  ox's  bile  is  due  to  an  in- 
gredient which  was  formerly  thought  to  be  mucin,  but  is  now 
regarded  as  a  nucleoproteid.  That  it  is  not  mncin  is  shown  by 
several  facts :  the  nitrogen  is  from  14  to  16  per  cent,  higher  than 
in  mucin,  and  when  boiled  with  a  mineral  acid  it  does  not  yield 
a  reducing  sugar.  This  substance  is  formed  by  the  epithelial  cells 
lining  the  gall-bladder. 


FIG.  139. — Portion  of  gall-bladder  and  bile-ducts:  1,  cavity  of  gall-bladder;  2, 
cavity  of  calyx;  3,  groove  separating  the  calyx  from  the  bladder;  4,  promontory; 
5.  superior  valve  of  calyx ;  6,  cystic  canal ;  7,  common  bile-duct ;  8,  hepatic  duct 

(Testut). 

The  bile  is  alkaline  in  reaction,  sodium  carbonate  and  alkaline 
sodium  phosphate  being  present  to  the  extent  of  about  0.2  per 
1000.  Its  color  varies:  in  herbivorous  animals  it  is  green;  in 
carnivorous  animals  golden  yellow  or  golden  red  ;  while  in  man  it 
is  of  a  golden  yellow,  though  often  green. 

Constituents  of  the  Bile. — The  chemical  composition  of  the  bile 
varies  in  the  same  individual  at  different  times,  and  this  differ- 
ence depends,  to  a  considerable  extent,  upon  the  length  of  time 


246 


THE  LIVER. 


it  remains  in  the  gall-bladder.  Analysis  will,  therefore,  vary 
materially,  according  as  the  secretion  is  removed  through  a  fistula 
of  the  bile-duct,  in  which  case  it  would  come  directly  from  the 
liver  or  from  the  gall-bladder  after  having  been  stored  there  for 
some  time. 

The  table  on  page  246  gives  the  results  of  various  analyses  of 
bile  which  have  been  made  by  competent  chemists. 

Bile-pigments. — These  are  two  :  bilirubin  and  biliverdin.  Both 
of  these  are  present  in  bile,  but  if  the  color  is  of  a  reddish  brown, 
as  in  the  carnivora,  the  bilirubin  predominates,  while  the  predomi- 
nance of  the  biliverdin  gives  the  greenish  hue,  the  characteristic 
color  of  the  bile  of  the  herbivora.  The  formula  for  bilirubin 
is  C16H18N2O3,  or,  as  given  by  some  writers,  C32H36N4O6 ;  that  of 
biliverdin,  CJ6H18N2O4  or  C32H36N4O8 — i.  e.,  the  former  passes  into 

Composition  of  Normal  Human  Bile. 


Bile  from  fistula. 

Bile  from  gall-bladder  immediately 
after  death. 

Copeman  and  Winston. 

Frerichs. 

Gorup-Besanez. 

Water    
Total  solids       ... 

985.77 
14.23 

6.28 
) 
0.99 

1.72 

4.51 

860. 
140. 

102.2 
1.6 

822.7 
177.3 

107.09 
47.3 

22.1* 

10.8 

Sodium  glycocholate  .    . 
Sodium  taurocholate 
Cholesterin       
Lecithin    
Fats       
Soaps             

3.2 

26.6 
6.5 

Mucin,  pigment,  etc. 
Inorganic  salts    .... 

the  latter  by  oxidation.  It  is  because  of  a  reduction  in  the  bili- 
verdin that  the  greenish  color  of  fresh  human  bile  becomes  red- 
dish after  it  has  remained  for  some  time  in  the  gall-bladder. 

In  clots  of  blood  that  are  old,  crystals  are  found  to  which  the 
name  fiematoidin  was  given  by  Virchow.  This  is  identical  with 
bilirubin.  Indeed,  it  is  now  conceded  that  the  pigments  of  the 
bile  are  derived  from  hemoglobin,  the  coloring-matter  of  the  blood. 
Thus  one  of  the  functions  of  the  liver-cells  is  to  change  the 
hemoglobin  which  comes  from  broken-down  red  blood-corpuscles 
to  bile-pigment,  separating  from  it  the  iron  and  preserving  it  for 
future  blood-making. 

Neither  bilirubin  nor  biliverdin  shows  any  absorption-bands 
with  the  spectroscope. 

Gmelin's  Test  for  Bile-pigment. — If  diluted  bile,  or  a  solution 
containing  bile-pigment,  is  poured  into  fuming  nitric  acid — i.  e., 
nitric  acid  containing  nitrous  acid,  which  is  a  powerful  oxidizing 
agent — there  will  be  produced  a  set  of  rings  or  zones  of  different 
colors,  according  to  the  amount  of  oxidation  of  the  bilirubin.  The 


BILE.  247 

zone  next  to  the  acid  will  be  the  most  oxidized,  and  will  be  of  a 
yellow-red  color  :  the  product  is  choletelin,  C16H18N2O6.  Above 
this  will  be  a  zone  of  red  or  purple,  becoming  blue  :  this  product 
is  called  bilicyanm  ;  above  all  will  be  a  green  zone,  biliverdin, 
which  being  farthest  from  the  acid  has  undergone  the  least  oxi- 
dation. This  constitutes  Gmelin's  reaction,  arid  is  employed  to 
detect  the  presence  of  bile-pigments,  as  in  the  urine.  A  modified 
form  of  applying  this  test  consists  in  wetting  a  piece  of  filter-paper 
with  bile,  or  the  solution  which  is  suspected  to  contain  bile, 
and  dropping  the  fuming  nitric  acid  upon  it,  when  the  character- 
istic colors  will  appear. 

Biliary  urine  gives  an  absorption  spectrum  showing  a  wide 
band  beginning  at  the  red  side  of  D  and  ending  between  D  and 
E.  Choletelin  gives  a  band  between  C  and  F. 

Hydrobilirubin.  —  This  substance  has  the  formula  C32H40N4O7. 
It  is  a  reduction-product  of  bilirubin,  and  is  obtained  by  the 
action  of  nascent  hydrogen,  from  sodium  amalgam,  in  an  alkaline 
solution  of  bilirubin.  It  gives  an  absorption  spectrum,  a  dark 
band  between  C  and  F.  It  is  with  difficulty  oxidized  to  bilirubin 
or  biliverdin.  Although  bilirubin  and  biliverdin  as  constituents 
of  the  bile  enter  the  intestine,  still  neither  is  found  in  the  feces, 
but  hydrobilirubin  is  there  found,  which  is  undoubtedly  derived 
from  the  bile-pigments.  This  pigment  of  the  feces  has  been 
described  as  stercobilin.  A  similar  pigment  in  the  urine  is  uro- 
bilin,  and  it  is  now  claimed  that  hydrobilirubin,  stercobilin,  and 
urobilin  are  one  and  the  same  substance. 

As  already  stated,  it  is  believed  that  bilirubin  comes  from 
hemoglobin,  the  coloring-matter  of  the  blood.  In  the  liver  this 
is  decomposed  into  a  proteid  and  hematin,  the  latter  containing 
iron.  The  hematin  takes  up  water,  the  liver-cells  remove  the 
iron,  and  bilirubin  is  formed.  This  may  be  expressed  by  the  fol- 
lowing equation  : 


+  2H20  -  Fe  =  C32H36N4O6  or  2(C16H18N2O3). 

Hematin.  Water.         Iron.  Bilirubin. 

Bile-salts.  —  These  are  sodium  glycocholate  and  sodium  tauro- 
cholate  —  i.  e.,  sodium  united  with  glycocholic  acid,  C^H^NOg,  and 
taurocholic  acid,  C26H45NSO7.  These  acids  are  known  as  bile-acids. 
Both  occur  in  human  bile,  as  a  rule,  though  taurocholic  acid  may 
be  absent.  When  glycocholic  or  taurocholic  acid  is  boiled  with 
an  acid  or  an  alkali,  it  takes  up  water  and  then  splits  up,  or,  as  it 
is  expressed,  "  undergoes  hydrolytic  cleavage/'  into  cholic  or  chola- 
lic  acid,  and  an  amido-acid  —  i.  e.,  an  organic  acid,  one  or  more  of 
whose  hydrogen  atoms  is  replaced  by  amidogen  (NH2).  Glyco- 
cholic acid  produces  glycocoll  or  amido-acetic  acid,  and  cholic  acid  ; 
while  taurocholic  acid  yields  taurin  or  amido-ethylsulphonic  acid. 
This  is  represented  by  the  following  equations  : 


248  THE  LIVER. 

.C26H43N06  +  H206  =  C^H^O,  +  C2H5M)2. 

Glycocholic  acid.       Water.         Cholic  acid.  Glycocoll. 

C^NSO,  +  H20  =  C24H4005  4-  C2H7NSO3. 

Taurocholic  acid.       Water.        Cholic  acid.  Taurin. 

A  similar  decomposition  of  the  bile-acids  is  believed  to  take 
place  in  the  intestine,  with  the  production  of  cholic  acid. 

Pettenkofer's  Test. — When  cane-sugar  and  strong  sulphuric  acid 
are  added  to  bile  or  a  solution  of  bile-salts  a  purplish  or  red- 
. dish-violet  color  is  produced.  This  is  due  to  the  action  of  the 
sulphuric  acid  on  the  cane-sugar,  producing  furfural  or  furfur- 
aldehyd,  and  this  acting  upon  the  cholic  acid  gives  the  characteris- 
tic color.  In  applying  this  test  the  temperature  should  be  kept 
below  70°  C.,  and  not  too  much  cane-sugar  added,  otherwise  it 
will  undergo  carbonization.  The  usual  way  of  performing  this 
test  is  to  add  to  a  few  drops  of  the  fluid  in  a  porcelain  capsule  a 
drop  of  strong  sulphuric  acid,  and  spread  out  the  mixture ;  then 
add  to  this  a  drop  of  a  10  per  cent,  solution  of  cane-sugar.  If 
the  color  does  not  appear,  the  capsule  should  be  warmed.  Inas- 
much as  the  test  depends  upon  the  reaction  between  furfural  and 
cholic  acid,  instead  of  using  cane-sugar,  a  drop  of  a  1  : 1000  solu- 
tion of  furfural  may  be  added  to  1  c.c.  of  an  alcoholic  solution  of 
bile-salts,  and  to  this  1  c.c.  of  concentrated  sulphuric  acid,  care 
being  taken  as  before  to  keep  down  the  temperature.  It  is  said 
that  the  presence  of  -^V  ^°  "sV  °^  a  milligram  of  cholic  acid  may 
be  recognized  by  the  furfural  test. 

Unfortunately,  Pettenkofer's  reaction  alone  cannot  be  relied 
upon  as  a  test  for  the  bile-salts,  inasmuch  as  proteids  and  other 
substances  to  the  number  of  forty  will  give  the  same  color.  The 
color  produced  by  cholic  acid  may,  however,  be  distinguished 
from  that  produced  by  all  other  substances  by  its  spectrum  ;  two 
bands,  one  between  the  solar  lines  D  and  E  near  to  E,  and  the 
other  at  F.  The  bile-acids  are  formed  by  the  cells  of  the  liver  ; 
probably  from  some  albuminoid  or  proteid  constituent.  They  are 
absorbed  by  the  intestine  and  are  not  excretory  products,  but  have 
various  offices  to  perform  and  for  which  they  are  produced;  just 
what  these  are  has  not  been  definitely  determined,  but  it  is 
regarded  as  probable  that  among  other  offices  is  that  of  dissolv- 
ing the  cholesterin,  which  would  otherwise  be  insoluble.  Other 
offices  will  be  referred  to  in  connection  with  the  discussion  of  the 
offices  of  the  bile  as  a  whole. 

Cholesterin. — The  formula  for  this  substance  is  C^H^O.  It  is 
found  not  only  in  bile,  but  also  in  nervous  tissue  and  in  the  cells 
of  plants  and  animals  (p.  101),  where  it  results  from  the  kata- 
bolic  processes  taking  place  in  them.  It  is  brought  to  the  liver 
by  the  blood,  and  is  not  formed  in  that  organ.  It  is  an  excretory 


BILK  249 

product,  and  the  function  of  the  liver,  so  far  as  this  substance  is 
concerned,  is  to  eliminate  it.  It  undergoes  no  changes  in  the 
intestine,  but  is  excreted  as  cholesterin  in  the  feces. 

Lecithin. — This  is  another  of  the  constituents  of  the  bile  which, 
like  cholesterin,  is  derived  from  nervous  tissue,  and  whose  elimina- 
tion from  the  blood  is  brought  about  by  the  liver-cells. 

Offices  of  the  Bile. — The  amount  of  bile  which  is  daily  secreted, 
being  about  800  or  900  grams  in  the  human  subject,  would 
indicate  that  its  offices  in  the  body  must  be  important.  It  is  a 
remarkable  fact  that  a  single  anatomic  element  can  perform  so 
many  varied  functions  as  does  the  liver-cell.  (1)  It  secretes  the 
water  of  the  bile;  not  alone,  for  the  cells  of  the  bile-ducts  and 
possibly  those  covering  the  lining  of  the  gall-bladder  aid  in  this 
process.  (2)  It  forms  the  bile-salts.  (3)  It  forms  the  bile-pig- 
ments. (4)  It  separates  cholesterin  and  lecithin  from  the  blood. 
Besides  these  functions,  all  of  which  are  related  to  the  bile,  it  has 
others  no  less  important  in  connection  with  the  formation  of  gly- 
cogen  and  urea,  both  of  which  are  discussed  elsewhere. 

That  the  passage  of  bile  into  the  intestine  is  not  essential  to 
life,  even  in  man,  is  conclusively  proved  by  the  results  of  the 
establishment  of  fistulse  of  the  gall-bladder  through  which  all  the 
bile  that  is  formed  is  removed  ;  indeed,  under  these  circumstances 
the  health  is  not  greatly  impaired. 

If,  however,  the  common  bile-duct  is  tied,  the  bile  which  is 
formed  is  absorbed  by  the  lymphatics,  an  exit  from  the  bile- 
duct  being  due  to  rupture  of  their  walls.  That  this  absorption  is 
not  into  the  blood-vessels  is  demonstrated  by  detecting  the  bile- 
pigments  and  the  bile-acids  in  the  lymph  as  it  is  discharged  from 
the  thoracic  duct  into  the  venous  system  at  the  junction  of  the 
left  internal  jugular  vein  with  the  left  subclavian  vein ;  the  result 
of  this  absorption  'is  to  produce  jaundice. 

Its  most  important  office  is  probably  the  part  which  it  plays  in 
serving  as  the  medium  through  which  cholesterin,  lecithin,  and 
other  results  of  katabolic  metabolism  are  removed.  Its  bile-acids 
are  to  a  certain  extent  absorbed  from  the  intestines  and  serve  as 
carriers  of  cholesterin.  Its  pigments  are  to  a  certain  extent  also 
absorbed  from  the  intestine,  though  what  advantage  results  there- 
from is  not  known.  Its  amylolytic  action,  if  it  possesses  any,  is 
exceedingly  slight,  and  it  has  no  proteolytic  power.  It  aids  the 
steapsin  of  the  pancreatic  juice  in  splitting  up  fat  into  its  fatty 
acids  and  glycerin,  and  it  furnishes,  as  we  have  seen,  alkaline  salts 
to  unite  with  fatty  acids  in  the  small  intestine  and  form  soaps, 
thereby  assisting  materially  in  the  em  unification  of  the  fats  which 
are  not  split  up. 

The  bile  aids  also,  probably  by  virtue  of  the  bile-salts,  in  the 
absorption  of  fats.  The  theory  that  the  bile-acids  dissolve  the  fat 
and  that  the  intestinal  walls  moistened  thereby  absorb  the  fat  more 


250  THE  LIVER. 

readily  because  the  contact  of  fat  and  membrane  is  closer  than 
it  otherwise  would  be,  i's  abandoned.  This  theory  was  based  on 
the  reputed  facts  that  oil  would  rise  higher  in  a  capillary  tube 
which  had  been  moistened  with  bile  than  in  one  which  had  been 
moistened  with  water,  and  that  a  filtering  medium  wet  with  bile 
would  permit  oil  to  pass  through  more  readily  than  one  wet  with 
water.  Experiment,  however,  demonstrates  that  these  are  not  facts.j 
In  view  of  the  present  belief  that  absorption  depends  not  upon 
osmosis,  but  upon  the  activity  of  lining  epithelium,  it  is  not 
improbable  that  the  cells  covering  the  mucous  membrane  of  the 
intestine  are  stimulated  by  the  bile-acids  to  increased  absorption 
of  fat. 

The  antiseptic  property  of  bile  is  very  small ;  still,  when  bile 
is  not  permitted  to  enter  the  intestine  putrefaction  of  the  intestinal 
contents  takes  place  more  readily  than  is  normal.  The  explana- 
tion of  this  is  not  satisfactory. 

Another  purpose  which  bile  subserves  is  to  precipitate  the  pro- 
teids  of  the  chyme  which  are  not  peptonized,  or  only  partially 
so,  as,  for  instance,  syntonin,  as  that  mixture  comes  into  the  intes- 
tine from  the  stomach.  With  this  precipitated  matter  is  also  some 
mucin  from  the  bile.  The  result  of  this  precipitation  is  a  tenacious 
mass  which  adheres  to  the  intestinal  wall,  and  which  is  therefore 
longer  exposed  to  the  action  of  the  digestive  fluids  of  the  intestine, 
and,  therefore,  more  perfectly  digested  than  it  otherwise  would  be. 

Innervation. — So  far  as  the  formation  of  bile  is  concerned, 
the  liver-cells  do  not-appear  to  be  supplied  with  secretory  nerves. 
There  is  great  difficulty  in  determining  this  question  with  cer- 
tainty, for  the  reason  that  in  stimulating  the  nerves  to  the  liver 
vasomotor  fibers  are  stimulated,  and  this,  of  course,  affects  the 
blood-supply  to  the  organ,  so  that  it  is  impossible  to  say  whether 
what  occurs  is  the  result  of  stimulating  secretory  nerves  or  of  an 
increased  supply  of  blood.  There  is  no  doubt,  however,  that  it 
is  to  the  blood  of  the  portal  vein  that  the  secretion  of  bile  must 
be  ascribed,  and  that  when  this  supply  is  increased  the  bile  secre- 
tion will  be  correspondingly  augmented.  This  occurs  during 
digestion,  and  it  is,  therefore,  at  this  time  that  the  amount  of  bile 
is  increased. 

It  is  probable  that  the  muscular  tissue  of  the  gall-bladder  and 
bile-ducts  is  supplied  with  nerves,  so  that  when  the  mucous  mem- 
brane of  the  stomach  or  intestine  is  stimulated  afferent  impulses 
reach  a  nerve-center  through  the  vagus,  and  efferent  impulses  pass 
out  and  are  carried  to  this  muscular  tissue  through  the  splanchnics  ; 
the  action  is,  in  other  words,  reflex. 

Movements  of  the  Small  Intestine. — When  the  food 
enters  the  small  intestine  through  the  relaxed  sphincter  pylori, 
the  free  hydrochloric  acid  present  brings  about,  by  contact  with 
the  duodenal  mucous  membrane  through  reflex  action,  a  closure 
of  the  pyloric  sphincter,  and  thus  the  quantity  of  food  material 


DIGESTION  IN  THE  LARGE  INTESTINE.  251 

passed  into  the  intestine  is  limited  and  the  power  of  the  intes- 
tine not  overtaxed.  Later,  the  acidity  is  neutralized  by  the  bile 
and  pancreatic  juice,  and  the  free  acid  in  the  stomach  causes 
a  relaxation  of  the  sphincter  and  another  portion  of  the  stomach- 
contents  enters  the  small  intestine.  Cannon  states  that  the  manner 
in  which  the  food  is  mixed  with  the  digestive  secretions,  exposed 
to  the  absorbing  wall,  and  carried  forward  in  the  small  intestine  is 
considerably  different  from  the  process  observed  in  the  large  in- 
testine and  in  the  stomach.  To  the  admirable  process  by  which 
these  functions  are  performed  in  the  small  intestine  he  has  given  the 
name  "  rhythmic  segmentation."  This  activity  of  the  muscular 
wall  is  first  seen  in  the  duodenum  when  a  mass  of  food  has  accu- 
mulated there  after  repeated  relaxations  of  the  pylorus.  The  mass 
of  food  is  observed  at  first  to  be  wholly  quiet.  Suddenly  irregular 
movements  take  place  about  it,  and  then  at  regular  intervals  along 
its  length  constrictions  of  the  circular  musculature  separate  the 
mass  into  a  number  of  segments  of  equal  size.  Hardly  have  the 
constrictions  thus  taken  place  when  similar  constrictions  begin  to 
appear  about  the  middle  of  each  segment.  As  these  new  constric- 
tions deepen,  the  first  constrictions  begin  to  relax.  Finally,  when 
the  new  constrictions  have  completely  divided  the  segments,  the 
first  constrictions  have  entirely  relaxed  and  the  neighboring  halves 
of  the  divided  segments  unite  to  form  new  segments  in  the  region 
of  the  first  constriction.  Now  these  new  segments  are  again  divided 
by  circular  constrictions  about  their  middle,  and  neighboring  halves 
of  these  divided  segments  unite  to  make  a  third  series,  and  so  on. 
This  process  of  rhythmic  segmentation  of  the  food  may  go  on  for 
several  minutes  in  the  duodenum  (at  the  rate  of  thirty  divisions 
per  minute  in  the  cat),  so  that  the  food,  coming  from  the  stomach, 
becomes  thoroughly  mixed  with  the  out-pouring  secretions  of  the 
liver  and  the  pancreas.  It  is  usual  for  the  process  to  be  brought 
to  an  abrupt  end  in  the  duodenum  by  active  peristalsis.  A  peri- 
staltic wave  forms  behind  the  mass  of  food  and  sweeps  it  swiftly 
forward  through  several  coils  of  the  intestine. 

The  movements  of  the  small  intestine,  like  those  of  the  stomach 
(p.  208)  and  large  intestine,  are  inhibited  whenever  the  animal 
experimented  upon  manifests  signs  of  anxiety,  rage,  or  distress. 

DIGESTION  IN  THE  LARGE  INTESTINE, 

Undoubtedly,  the  process  of  intestinal  digestion,  which  is 
mainly  carried  on  in  the  small  intestine,  is  continued  to  some 
extent  in  the  large  intestine,  as  the  conditions  there  existing  are 
favorable  to  a  continuance  of  this  process,  but  the  enzymes,  which 
are  the  efficient  agents,  are  those  of  the  fluids  which  have  come 
with  the  food  into  the  large  intestine,  the  mucous  membrane  here 
producing  no  enzymes  with  digestive  powers.  In  studying  the 
process  of  absorption  we  shall  see  that,  although  the  large  intes- 


252  DIGESTION  /JV  THE  LARGE  INTESTINE. 

tine  possesses  no  digestive  power,  it  has  considerable  power  of 
absorption. 

Movements  of  the  I/arge  Intestine. — In  the  cecum,  as- 
cending and  transverse  colon,  the  normal  activity,  according  to 
Cannon,  is  an  antiperistalsis.  Constriction  waves  start  in  the 
transverse  colon  and  pass  backward  toward  the  cecum.  These 
waves,  unlike  those  of  the  stomach,  do  not  run  in  continuous 
rhythm ;  they  occur  usually  in  periods  lasting  about  five  minutes, 
and  recur  every  fifteen  or  thirty  minutes.  He  says  :  "  The  anti- 
peristalsis  in  this  part  of  the  large  intestine  seems,  indeed,  to 
give  a  reason  for  the  presence  of  a  valvular  structure  at  the  en- 
trance of  the  small  intestine  into  the  large.  Hundreds  of  anti- 
peristaltic  waves  have  been  seen  coursing  toward  the  cecum,  and 
only  twice  has  food  been  observed  to  be  pressed  back  into  the 
ileum  through  the  ileocolic  valve.  Inasmuch  as  the  valve  is  com- 
petent for  the  food  which  has  gone  from  the  small  into  the  large 
intestine,  the  antiperistaltic  waves  have  the  same  effect  here  as  the 
peristaltic  waves  have  in  the  stomach  when  the  pylorus  remains 
closed.  For,  when  a  constriction  occurs,  some  of  the  mucous  sur- 
face of  the  colon  becomes  enclosed  by  the  narrowed  muscular  ring ; 
and,  as  this  constriction  passes  on,  fresh  areas  of  this  surface  are 
continually  pressed  inward  around  the  narrow  orifice,  while  a  thin 
stream  of  food  is  passing  in  the  opposite  direction.  As  waves 
recur  about  five  times  a  minute,  twenty-five  waves  or  more  affect 
every  particle  of  food  in  the  cecum  and  in  the  ascending  colon  in 
this  churning  manner  during  each  normal  period  of  antiperistalsis. 
The  result  must  be  again  a  thorough  mixing  of  the  contents  with 
the  digestive  secretions  brought  from  the  small  intestine  and  an 
exposure  of  the  digested  food  to  the  absorbing  wall. 

"  Immediately  after  food  passes  from  the  ileum  into  the  large 
intestine  a  strong  tonic  contraction  of  the  cecum  and  the  ascending 
colon  is  commonly  observed,  which  serves  to  press  onward  to- 
ward the  rectum  the  contents  of  these  parts.  Antiperistaltic  waves 
follow  at  once  the  general  contraction,  so  that  much  of  the  food 
which  has  been  pressed  onward  is  returned  into  the  cecum.  With 
the  repetition  of  this  process,  however,  more  and  more  material 
appears  at  the  end  of  the  transverse  colon,  and  on  its  appearance 
there  a  persistent  ring  of  contraction  cuts  it  off  from  the  region  of 
antiperistalsis ;  as  still  more  food  appears  in  the  large  intestine  this 
ring  moves  slowly  Onward  toward  the  rectum,  pressing  a  mass  before 
it,  and  is  followed  by  other  similar  rings  carrying  onward  similar 
masses  by  very  slow  peristalsis. 

"  Thus,  in  the  large  intestine  the  function  of  mixing  the  food  with 
the  digestive  secretions  and  of  exposing  this  food  to  the  absorbing 
walls  is  performed  by  an  antiperistalsis  at  the  beginning  of  the 
large  intestine.  It  is  here  that  the  last  valuable  constituents  of  the 
food  are  worked  over  and  taken  into  the  body.  The  remnant  of 
unused  material  is  propelled  onward  by  occasional  strong  contrac- 


BACTERIAL  DIGESTION. 


tions  of  the  whole  region  of  antiperistalsis.  These  contractions 
squeeze  the  material  toward  the  end  of  the  transverse  colon  where 
slowly-moving  peristaltic  waves  force  it  to  the  rectum." 

These  movements,  as  in  the  case  with  the  stomach  and  small 
intestine,  are  inhibited  by  rage,  anxiety,  or  distress. 

BACTERIAL  DIGESTION. 

Bacteria  are  found  in  considerable  numbers  in  the  mouth, 
stomach,  and  intestine ;  more  than  sixty  species  are  recorded 
by  Sternberg  as  having  been  found  in  the  mouth  ;  and  seventy- 
four  have  been  isolated  from  feces  and  the  intestines  of  cadavers. 
Those  which  occur  in  the  stomach  consist  of  mouth-bacteria  which 
have  been  swallowed  together  with  bacteria  which  are  in  the  food 
and  drink.  We  have  already  referred  to  some  of  the  pathogenic 
or  disease-producing  bacteria,  and  the  effect  of  hydrochloric  acid 
upon  them  (p.  196).  But  besides  these  there  are  others  which  have 
a  true  digestive  action  on  the  food-stuffs.  Inasmuch  as  there  is  no 
free  hydrochloric  acid  in  the  stomach  for  about  half  an  hour  after 
food  has  entered  it,  the  antiseptic  action  of  this  acid  is  not  exerted 
for  that  length  of  time,  and  the  conditions  are  favorable  for  bacterial 
action.  During  this  time  some  of  the  carbohydrates  may  be  decom- 
posed, with  the  result  of  producing  lactic  and  other  acids  and  set- 
ting free  hydrogen  gas.  Proteids  do  not,  however,  appear  to  be 
acted  upon  by  bacteria  in  the  stomach.  In  the  small  intestine 
there  is  some  decomposition  of  proteids,  but  not  to  any  considerable 
extent.  Lactic  and  other  organic  acids  are,  however,  produced 
from  carbohydrates.  These  changes  in  both  proteids  and  carbo- 
hydrates are  due  to  the  action  of  bacteria. 

The  action  of  the  intestinal  bacteria  upon  proteids  has  been 
likened  to  that  of  trypsin.  The  proteid  is  dissolved,  and  then 
changed  into  albumoses  and  peptones.  A  part  goes  on  to  the 
stage  of  tyrosin,  which  becomes  still  further  decomposed  into 
paraoxyphenylpropionic  acid,  paraoxyphenylacetic  acid,  phenol, 
and  parakresol.  From  another  portion  of  the  proteid  are 
formed  indol,  skatol,  and  skatolcarbonic  acid.  These  substances 
are  not  derived  from  tyrosin  nor,  indeed,  from  peptones,  but 
from  some  unknown  intermediate  substance  derived  from  the 
proteid  itself. 

All  of  the  carbohydrates  of  the  food  seem  to  be  subject  to 
bacterial  action.  Thus  starch  and  even  cellulose  may  be  decom- 
posed by  the  appropriate  bacteria.  As  results  of  carbohydrate 
decomposition  are  produced  ethyl  alcohol,  lactic,  butyric,  and 
succinic  acids,  together  with  carbon  dioxid  and  hydrogen. 

The  fats  are  normally  unchanged  by  bacterial  action ;  in  the 
absence  of  bile  or  pancreatic  juice  they  are  decomposed,  with  the 
formation  or  fatty  acids. 

It  is  claimed  that  one  important  office  performed  by  the  intesti- 
nal bacteria  is  to  prevent  putrefaction. 


254  ABSORPTION  OF  THE  FOOD. 

From  all  the  facts  known  in  connection  with  bacteria,  the  con- 
clusion is  inevitable  that  they  serve  a  useful  purpose  in  the  econ- 
omy ;  they  may,  however,  when  in  excess,  produce  such  amounts  of 
harmful  substances  as  to  be  injurious  when  these  are  absorbed. 

ABSORPTION  OF  THE  FOOD. 

Attention  has  already  been  called  to  the  fact  that  a  large  part 
of  the  food-stuffs  taken  into  the  body  are  not  .in  a  condition  to  be 
absorbed  by  the  blood,  nor  to  be  utilized  by  the  tissues  when 
brought  to  them  by  that  fluid  (p.  167),  and  that  digestion  consists 
in  bringing  about  the  changes  in  them  necessary  to  effect  this 
result.  It  is  these  changes  which  we  have  studied,  and  which 
will  prepare  us  to  understand  the  process  of  absorption. 

Manifestly,  absorption  might  take  place  anywhere  in  the  alir 
mentary  tract  from  the  mouth  to  the  anus,  but  it  has  been  demon- 
strated that  in  some  portions  of  this  canal  very  little  absorption, 
if  any,  takes  place,  and  that  in  others  the  greater  part  of  the  proc- 
ess is  carried  on. 

Mouth-absorption. — Under  ordinary  circumstances  there 
is  no  absorption  while  substances  are  in  the  buccal  cavity.  This 
is  certainly  true  for  the  food-stuffs,  though  that  it  may  occur 
for  some  other  substances  is  proved  by  the  fact  that  cyanid  of 
potassium  taken  into  the  mouth  and  retained  there  will  produce 
death. 

There  is  likewise  no  absorption  while  food  is  passing  through 
the  esophagus ;  the  time  occupied  in  the  transit  is  altogether  too 
brief,  and  the  conditions  generally  are  unfavorable. 

Gastric  Absorption. — The  food-stuffs  which  enter  the  stom- 
ach are:  (1)  inorganic,  water  and  salts;  (2)  carbohydrates,  starch 
and  sugars ;  (3)  fats  or  oils ;  and  (4)  proteids. 

Inorganic  Food-stuffs. — Water  taken  into  the  stomach  by  itself 
is  not  absorbed  to  any  extent  by  that  organ.  Von  Mering  demon- 
strated this  in  a  dog  in  which  he  first  established  a  fistula  in  the 
duodenum,  and  then  gave  it  by  the  mouth  500  c.c.  of  water. 
Almost  as  soon  as  it  reached  the  stomach  it  was  forced  out  by 
contraction  of  the  muscular  coat  into  the  duodenum  in  spirts,  and 
in  twenty-five  minutes  495  c.c.  passed  out  through  the  fistulous 
opening  in  the  intestine.  When  water  contains  in  solution  sub- 
stances which  are  absorbed  by  the  stomach-walls,  some  of  the 
water  is  also  absorbed  with  them. 

The  evidence  as  to  the  absorption  of  salts  is  very  incomplete. 
Sodium  iodid  in  3  per  cent,  solution  is  absorbed,  but  to  a  slight 
extent  if  the  solution  is  more  dilute.  Many  substances,  such  as 
mustard  or  alcohol,  hasten  its  absorption,  probably  by  stimulating 
the  epithelium. 

Carbohydrates. — Starch  is  not  absorbed  as  such,  but  must  be 
changed  into  maltose,  which  process,  as  we  have  seen,  does  take 


ABSORPTION  BY  THE  SMALL  INTESTINE.  255 

place  to  no  inconsiderable  extent  in  the  stomach  ;  although  it  also 
is  carried  on  more  energetically  in  the  small  intestine.  All  varie- 
ties of  sugar — dextrose,  lactose,  saccharose,  and  maltose — are 
absorbed  in  the  stomach,  and  this  is  also  true  of  dextrin.  Some 
of  the  saccharose  is  inverted  to  dextrose  and  levulose  in  the 
stomach,  and  doubtless  absorbed  in  this  form  to  some  extent, 
while  the  rest  of  it  undergoes  the  same  change  in  the  small  intes- 
tine. It  is  essential,  however,  that  the  solution  should  be  concen- 
trated ;  at  least  this  is  true  of  dextrose,  of  which  very  little  is 
absorbed  until  the  concentration  equals  5  per  cent.,  and  the  rate 
of  absorption  increases  up  to  a  concentration  of  20  per  cent. 
Alcohol  causes  increased  absorption  of  sugar,  as  it  does  of  sodium 
iodid,  and  doubtless  for  the  same  reason.  Taken  as  a  whole,  the 
amount  of  the  sugars  absorbed  from  the  stomach  is  probably  not 
great. 

Peptones. — These  are  also  absorbed  from  the  stomach,  though, 
as  in  the  case  of  dextrose,  only  when  the  concentration  reaches  5 
per  cent.,  so  that  the  absorption  of  peptones  from  the  stomach  is 
relatively  small. 

Fats  and  Oils. — With  the  exception  of  the  physical  change, 
due  to  the  temperature  of  the  stomach,  by  which  the  fats  and  oils 
are  rendered  more  fluid,  and  their  probable  splitting  up  into  fatty 
acids  (p.  199),  no  change  takes  place  in  them,  nor  are  they  absorbed 
to  any  extent  whatever. 

Alcohol. — The  fact  that  alcohol  is  readily  absorbed  from  the 
stomach  has  been  sufficiently  dwelt  upon  (p.  161). 

From  the  above  considerations  it  will  be  seen  that  gastric  ab- 
sorption is  not  a  process  of  much  importance ;  indeed,  the  cases 
of  the  entire  removal  of  this  organ,  to  which  we  have  referred, 
demonstrate  that  the  exercise  of  what  little  absorptive  power  it 
possesses,  is  unnecessary.  We  desire  to  direct  special  attention 
to  the  fact  that  sodium  iodid,  dextrose,  and  peptones  are  more 
readily  absorbed  when  alcohol  is  also  present.  This  empha- 
sizes the  view  now  held  as  to  absorption, — that  it  is  not  a  mere 
matter  of  osmosis,  but  is  due  to  an  actual  selective  power  of 
the  epithelial  cells,  and  that  this  is  more  actively  exercised  under 
the  stimulating  action  of  alcohol  or  other  substances  having  like 
power. 

Absorption  by  the  Small  Intestine. — It  is  from  the 
cavity  of  the  small  intestine  that  the  greater  part  of  absorption 
takes  place,  the  products  of  digestion  passing  into  the  villi,  a  part 
entering  the  capillary  blood-vessels  and  reaching  the  liver  through 
the  portal  vein  ;  while  another  part  enters  the  lacteals,  and  passes 
on  into  the  thoracic  duct,  from  which  it  is  discharged  into  the 
blood-vascular  circulation.  While  osmosis  is  doubtless  one  of  the 
factors  in  this  process,  still  the  selective  power  of  living  cells 
is  much  more  potent. 


256  ABSORPTION  OF  THE  FOOD.. 

The  materials  to  be  absorbed  are :  (1)  water,  salts ;  (2)  carbo- 
hydrates ;  (3)  fats ;  (4)  proteids. 

Absorption  of  Water. — As  was  stated  in  connection  with  gastric 
absorption  (p.  254),  water  is  not  absorbed  to  any  extent  from  that 
organ,  most  of  that  taken  in  being  passed  on  into  the  small  intes- 
tine. Experiments  have  shown  that  the  water  which  enters  the 
small  intestine  is  absorbed  by  the  capillaries  of  the  villi ;  and  yet 
even  when  large  quantities  are  absorbed,  an  analysis  of  the  blood 
shows  no  change,  as  might  be  expected,  the  excess  being  elimi- 
nated by  the  kidneys. 

Absorption  of  Carbohydrates. — The  dextrose  and  levulose,  formed 
by  the  action  of  the  enzymes,  are  absorbed  by  the  veins  and 
carried  by  the  portal  vein  to  the  liver,  but  there  is  evidence  that 
saccharose,  and  even  dextrin  and  starch,  can  be  taken  up  by  the 
cells;  although,  as  we  have  seen,  the  action  of  the  intestinal 
enzymes  is  very  powerful,  and  doubtless  the  amount  of  carbo- 
hydrates remaining  in  any  other  condition  than  that  of  dextrose 
or  levulose  is  very  small.  But,  even  if  carbohydrates  should  be 
absorbed  in  any  form  but  these,  they  would  be  inverted  while1 
passing  through  the  cells.  It  is  a  remarkable  fact  that  lactose, 
which  forms  so  important  a  part  of  the  milk,  the  sole  food  of  the 
growing  child,  is  unaffected  by  the  enzymes  ;  however,  in  its  pass- 
age through  the  epithelial  cells  it  is  inverted,  the  product  being 
probably  dextrose  and  galactose.  Maltose,  also,  may  be  inverted 
by  the  columnar  epithelium. 

It  is,  then,  mostly  in  the  form  of  dextrose  and  levulose  that 
the  carbohydrates  of  the  food  enter  the  blood  and  are  carried  to 
the  liver,  and  from  these  glycogen  is  formed.  Saccharose  and 
maltose  cannot  be  thus  changed  by  the  liver-cells.  It  sometimes 
happens  that  very  large  quantities  of  sugar  are  taken  in  with 
the  food ;  if  the  amount  is  so  great  that  the  liver  and  muscles  can- 
not convert  it  all  into  glycogen,  the  overplus  is  eliminated  by  the 
kidney,  and  appears  in  the  urine,  constituting  alimentary  glycosuria. 

Glycogenic  Function  of  the  I/iver. — As  we  have  seen, 
the  result  of  the  digestion  of  starch  is  its  conversion  into  mal- 
tose, or  maltose  and  dextrin,  which  later  becomes  dextrose,  in 
which  form,  for  the  most  part,  the  carbohydrates  of  the  food 
reach  the  liver.  Some  levulose  may  accompany  it  to  the  liver, 
where,  according  to  some  authorities,  it  becomes  dextrose.  If 
during  the  time  of  the  absorption  of  sugar  the  blood  going  to 
the  liver  through  the  portal  vein  and  that  coming  from  it  by 
the  hepatic  vein  are  analyzed,  it  will  be  found  that  the  former 
contains  much  more  sugar  than  the  latter ;  from  this  fact  the 
inference  is  inevitable  that  some  change  takes  place  in  the  sugar 
during  its  passage  through  the  liver.  This  change  consists  in  its 
conversion  by  the  hepatic  cells  into  glycogen,  which  is  a  process 
of  dehydration,  the  reverse  of  what  takes  place  when  the  starch  or 
glycogen  of  the  food  is  converted  into  sugar. 


GLYCOGENIC  THEORY.  257 

Formation  of   Glycogen   from  Carbohydrates. — The 

liver  weighs  between  1500  and  1900  grams,  and  as  the  amount 
of  glycogen  in  this  organ  may  reach  10  per  cent,  of  its  weight, 
150  to  190  grams,  it  is  manifest  that  the  carbohydrates  of  a  single 
meal,  which  would  ordinarily  amount  to  about  100  or  150  grams, 
could  be  stored  as  glycogen  in  the  liver,  provided  that  before  the 
next  meal  this  was  all  reconverted  into  liver-sugar,  and  as  such 
passed  out  into  the  blood,  leaving  the  liver  free  from  glycogen ; 
but  this  does  not  occur,  so  that  we  may  conclude  that  all  the 
carbohydrates  are  not  deposited  in  the  liver.  As  has  been 
stated  (p.  62),  the  muscles  contain  glycogen,  sometimes  to  the 
amount  of  1  per  cent.,  and  this  undoubtedly  comes  from  the 
carbohydrates  of  the  food.  If,  however,  all  the  glycogen  in  the 
liver  and  the  muscles  is  taken  into  account,  together  with  the 
dextrose  in  the  blood,  about  0.12  per  cent.,  there  still  remains  an 
overplus  unaccounted  for,  and  this  is  believed  to  enter  into  the 
formation  of  proteids  and  other  substances ;  indeed,  it  is  not  by 
any  means  certain  but  that  some  of  the  absorbed  dextrose  may 
exist  in  the  blood  as  dextrose  and  never  undergo  conversion  into 
glycogen,  but  perform  the  same  office  as  the  dextrose  which  does 
result  from  liver  or  muscle  glycogen — i.  e.,  serve  as  a  source  of 
energy. 

Formation  of  Glycogen  from  Proteids. — It  has  been 
abundantly  demonstrated  that  feeding  animals  on  proteids  alone, 
without  any  admixture  with  carbohydrates,  results  in  the  forma- 
tion of  glycogen  in  both  liver  and  muscles.  It  follows  from  this 
that  there  exists  in  the  body  the  power  of  decomposing  proteids, 
and  from  the  carbon,  hydrogen,  and  oxygen  which  enter  into  their 
composition  to  form  glycogen.  By  this  statement  it  is  not  in- 
tended to  convey  the  idea  that  the  proteid  is  broken  up  into  its 
chemical  elements,  but  rather  that  it  is  decomposed  into  a  non- 
nitrogenous  and  a  nitrogenous  portion  ;  the  non-nitrogenous  portion 
becoming  ultimately  glycogen,  possibly  passing  through  a  prelimi- 
nary stage  of  dextrose,  some  of  which  may  remain  as  dextrose, 
and  not  undergo  conversion  into  glycogen. 

Formation  of  Glycogen  from  Fats. — It  is  generally 
accepted  that  no  glycogen  is  formed  from  fat.  There  are  authori- 
ties, however,  who  hold  the  contrary  opinion,  basing  this  upon  cer- 
tain experiments,  and  upon  the  fact  that  in  germinating  seeds  such  a 
change  does  take  place.  It  may  be  regarded  as  an  unsettled  question. 

It  is  an  interesting  fact  that  liver-glycogen  is  increased  upon 
the  administration  of  glycerin.  While  glycerin  is  not  convertible 
into  glycogen,  it  seems  to  prevent  the  change  of  the  glycogen  in 
the  liver  into  dextrose,  and  hence  causes  its  retention,  which  has 
the  same  effect  upon  the  total  amount  in  the  liver  as  if  more  had 
been  formed. 

Glycogenic  Theory. — The  carbohydrates  serve  as  sources 
of  energy — i.  e.,  they  are  oxidized  to  CO2  and  HoO  in  the  body, 

17 


258  ABSORPTION  OF  THE  FOOD. 

and  heat  and  work  are  the  result  of  this  oxidation.  The  various 
stages  through  which  they  pass  are  not  all  known,  but  as  to  some 
there  seems  little  doubt.  Thus  the  formation  of  dextrose  and 
levulose,  during  digestion  and  absorption,  and  the  deposition  of 
the  greater  part  of  these  in  the  liver  and  muscles  as  glycogen,  are 
generally  accepted;  but  as  to  what  changes  take  place  in  the 
glycogen  there  is  a  difference  of  opinion. 

"  Theory  of  Claude  Bernard. — The  opinion  advanced  by  this 
distinguished  physiologist,  who,  in  the  year  1848,  discovered  that 
sugar'was  formed  in  the  liver,  and  in  1857  that  it  had  its  origin 
in  glycogen,  was  that  the  dehydration  of  the  dextrose  by  the  liver- 
cells,  by  which  glycogen  is  deposited  in  that  organ,  is  a  provision 
for  the  storage  of  the  carbohydrates  of  the  food  ;  otherwise  the  dex- 
trose, after  it  had  reached  a  percentage  above  that  which  normally 
exists  in  the  blood,  0.1  to  0.2  per  cent.,  would  be  of  no  use  to  the 
body,  inasmuch  as  it  would  be  eliminated  by  the  kidneys.  But, 
being  stored  up  in  the  liver  at  the  time  of  its  absorption,  it  is,  in 
the  intervals  of  digestion,  gradually  converted  into  dextrose,  which 
passes  out  in  the  blood  of  the  hepatic  veins  and  serves  the  body 
as  a  source  of  energy.  It  is  a  matter  which  is  still  in  doubt 
whether  this  conversion  is  a  zymolytic  action — i.  e.,  whether  it 
is  produced  by  an  enzyme  or  by  the  liver-cells  as  one  of  their 
peculiar  functions.  The  argument  against  the  change  being  due 
to  an  enzyme  is,  that  while  amylolytic  enzymes  have  been  found  in 
the  liver,  which  change  glycogen  to  maltose,  here  is  a  change 
to  dextrose ;  but,  on  the  other  hand,  a  ferment  has  been  obtained 
from  the  liver  which  does  convert  glycogen  into  dextrose,  so  that 
this  argument  has  but  little  weight.  That  the  power  to  change 
glycogen  into  dextrose  resides  in  tissues  independently  of  the  pres- 
ence of  enzymes  is  shown  by  the  fact  that  the  muscles  of  the 
body,  during  the  entire  life  of  an  individual,  and  other  organs, 
such  as  the  placenta,  during  fetal  life,  have  the  same  power  as  the 
liver  to  form  glycogen  from  the  dextrose  of  the  blood.  While 
Bernard's  theory  has  been  generally  accepted  by  physiologists, 
there  are  those  who  oppose  it,  and  among  these  the  most  promi- 
nent is  Pavy. 

Theory  of  Pavy. — Pavy  regards  the  dextrose  which  Bernard  and 
others  have  found  in  the  hepatic  vein  as  due  to  a  change  brought 
about  by  the  action  upon  the  glycogen  of  an  enzyme  formed  in 
the  liver  after  death.  His  analyses  of  the  blood  of  the  ascending 
vena  cava,  which  carries  the  blood  coming  from  the  liver,  show 
no  increase  of  sugar  over  the  blood  obtained  from  other  portions 
of  the  circulation,  provided  that  it  is  examined  before  post-mortem 
changes  have  set  in.  For  this  purpose  he  kills  the  animal  by 
a  blow  upon  the  head,  and  immediately  withdraws  the  blood. 
[According  to  this  theory,  during  life  the  glycogen  of  the  liver 
*  does  not  become  converted  into  dextrose,  but  is  a  source  of  fat  and 
(of  proteid.  That  fat  is  formed  in  th,e  body  in  considerable  amount 

"*£ J± 


DIA  BETES.  259 

on  a  carbohydrate  diet  is  a  well-known  fact,  and  one  of  the  re- 
strictions placed  upon  obese  individuals  who  are  endeavoring;  to 
reduce  their  fat  is  to  abstain  from  sugar  as  much  as  possible.  The 
glycogen  of  the  muscles  may  also  serve  for  the  purpose  of  fat 
formation.  That  glycogen  serves  also  as  a  source  of  energy  there 
is  no  doubt. 

It  may  seem  to  the  student  a  strange  fact  that  what  appears  so 
simple  a  matter  to  determine  as  this  which  is  in  dispute  between 
the  adherents  of  the  two  theories  referred  to  cannot  be  definitely 
settled  ;  but  it  is  to  be  borne  in  mind  that  the  blood  is  a  very 
complex  fluid,  and  the  methods  for  detecting  with  certainty  the 
amount  of  sugar  in  the  blood  are  not  sufficiently  exact  to  warrant 
a  positive  statement,  for  in  this  fluid  there  are  other  reducing 
substances  than  sugar.  Then,  too,  it  must  be  remembered  that 
the  entire  blood  of  the  body  passes  through  the  liver  every  two 
minutes,  so  that  while  the  total  amount  of  sugar  passed  out  from 
that  organ  in  twenty-four  hours  might  be  considerable,  yet  the 
difference  in  amount  found  at  any  given  moment  in  the  blood  of 
the  hepatic  vein,  over  and  above  that  found  in  other  parts  of  the 
circulation,  would  be  so  small  as  not  to  be  within  the  possibility 
of  determination.  In  view  of  the  conflicting  evidence  we  must, 
therefore,  acknowledge  that  the  question  is  still  an  open  one,  with 
the  weight  of  evidence  at  the  present  time  in  favor  of  the  theory 
of  Bernard. 

Diabetes. — This  is  "  an  affection  characterized  by  an  immoder- 
ate and  morbid  flow  of  urine."  When  there  is  no  sugar  in  such 
urine  the  condition  is  called  diabetes  insipidus ;  but  when  the 
urine  contains  an  abnormal  amount  of  sugar,  diabetes  mellitus,  or 
simply  diabetes.  The  term  glycosuria  refers  to  the  excessive 
amount  of  sugar  in  the  urine,  and  this  condition  may  exist,  tem- 
porarily, in  other  affections  than  diabetes.  The  form  in  which  the 
sugar  exists  is  principally  that  of  dextrose,  though  there  is  doubt- 
less some  maltose  also  present.  The  source  of  this  sugar  may  be 
from  glycogen  or  from  proteids.  If  from  the  former,  it  may  be 
caused  by  excessive  conversion  of  glycogen  into  dextrose  (Ber- 
nard), or  from  a  failure  on  the  part  of  the  liver  to  convert  into 
glycogen  as  much  of  the  absorbed  sugar  as  occurs  normally  (Pavy). 
Whichever  view  is  taken,  the  treatment  consists,  among  other 
things,  in  depriving  the  patient  of  all  foods  which  make  sugar. 
In  some  cases,  however,  even  after  this  is  done,  the  glycosuria 
continues,  and  the  only  possible  explanation  is  that  the  sugar  is 
produced  from  proteids. 

Artificial  Diabetes. — The  condition  of  glycosuria  may  be  arti- 
ficially produced  : 

(1)  Puncture-diabetes. — Puncture  in  the  floor  of  the  fourth 
ventricle  of  the  brain,  the  region  in  which  is  situated  the  vaso- 
motor  center,  will  cause  glycosuria.  This  center  is  stimulated 
by  the  puncture,  the  arterioles  of  the  liver  are  constricted^,  thus 


260  ABSORPTION  OF  THE  FOOD. 

reducing  the  amount  of  arterial  blood  in  that  organ,  which  results 
in  an  increased  activity  of  the  liver-cells,  thereby  causing  an 
excessive  conversion  of  glycogen  into  sugar.  This  is  one  expla- 
nation which  has  been  given  to  account  for  the  phenomenon. 
Another  is  that  the  glycosuria  is  due  to  a  direct  action  upon 
the  secretory  nerves  of  the  liver. 

(2)  Phlorizin-dlabetes. — Glycosuria  may  also  be  produced  by  the 
administration  of  a  number  of  different  substances;  among  these 
are  phosphoric  and   lactic  acids,  strychnin,  arsenic,  phosphorus, 
and  especially  phloridzin  or  phlorizin,  a  bitter  substance,  having 
the  chemical  formula  Cg^^O^,  obtained  from  the  bark  of  the 
root  of  the  apple-,  pear-,  and  cherry-tree.     Phlorizin  is  a  glucosicl. 
A  glucosid   is  a  vegetable   principle   which,  when    treated   with 
acids  and  some  other  substances,  yields  glucose  and  another  sub- 
stance which  is  characteristic  of  the  particular  plant  from  which 
the  glucosid  was  obtained.     There  are  many  glucosids  which  have 
been  isolated ;  among  these  are,  amygdalin,  from  bitter  almonds  ; 
digitalin,  from  digitalis ;  esculin,  from  the  horse-chestnut,  etc.     It 
was  thought  at  one  time  that  the  glycosuria  which  follows  the 
administration  of  phlorizin  was  due  to  the  glucose  which  it  con- 
tains, but  it  is  now  known  that  phloretin,  which  is  a  crystalline 
substance  formed  by  the  action  of  an  acid  on  phlorizin,  and  which 
contains  no  glucose,  will   have   the  same  effect  as  the  phlorizin 
itself. 

(3)  A  diabetic  condition  may  also  be  produced  by  removing  the 
pancreas.     Of  this  form  of  glycosuria  we  have  already  spoken 
(p.  239). 

Absorption  of  Proteids. — The  theory  that  the  digestion 
of  proteids  consists  in  their  being  changed  into  a  more  diffusi- 
ble form,  and  that  in  this  condition  they  are  absorbed  by 
the  physical  process  of  osmosis,  has  been  to  a  considerable 
degree  abandoned.  For  while  it  is  true  that  proteoses  and 
peptones  are  diffusible,  while  native  albumins  are  not,  still  it  has 
been  shown  that  egg-albumin  is  absorbed  as  such,  although  it 
is  non-diffusible.  This  absorption  takes  place  in  both  the  small 
and  large  intestine ;  in  the  former,  under  circumstaaces  which 
demonstrate  that  it  could  not  have  been  previously  peptonized, 
and  in  the  latter,  of  course,  there  is  no  peptonizing  enzyme.  We 
must,  therefore,  attribute  the  absorption  of  proteids  to  the  epithe- 
lial cells,  to  whose  efficiency  in  the  process  of  absorption  we  have 
so  frequently  had  occasion  to  refer.  Not  only  is  egg-albumin 
absorbed,  but  the  same  is  true  of  syntonin  as  well.  There  is  this 
difference,  however,  that  when  egg-albumin  is  absorbed  in  such 
quantity  that  it  cannot  be  changed  into  an  assimilable  form  while 
passing  through  the  cells  of  the  villi,  it  is  carried  by  the  blood  to 
the  kidneys,  where  it  is  eliminated,  producing  an  "alimentary 
alburninuria,"  while  syntonin  is  utilized  by  the  tissues.  There 
is  little  doubt  that  it  is  in  the  form  of  proteoses  and  peptones 


ABSORPTION  OF  FAT.  261 

that  the  proteids  are  absorbed,  and  that  the  capillary  blood-vessels 
of  the  villi  are  the  efficient  agents  in  this  process.  Some  recent 
experimenters,  Asher  and  Barbera,  claim  that  some  proteid  is 
absorbed  by  the  lacteals,  but  Mendel  conducted  an  investigation 
as  a  result  of  which  he  concludes  that  "  under  ordinary  circum- 
stances by  far  the  greater  share  in  the  process  must  still  be  dele- 
gated to  the  capillaries  of  the  villi." 

Although  proteids  are  mainly  absorbed  as  proteoses  and  pep- 
tones, yet  during  this  act  they  lose  their  identity.  In  other  words, 
while  passing  through  the  epithelial  cells  which  cover  the  villi  they 
are  so  changed  that  neither  proteose  nor  peptone  can  be  found  in 
the  blood,  and  if  these  substances  are  directly  injected  into  the  blood 
they  are  eliminated  by  the  kidneys  and  are  found  in  the  urine. 
Indeed,  if  the  amount  is  sufficient  they  act  as  poisons,  causing 
insensibility,  lowering  blood-pressure,  diminishing  or  destroying 
the  coagulability  of  the  blood,  and  producing  death.  Although 
the  power  to  convert  proteoses  and  peptones  into  a  form  which 
can  be  assimilated  is  claimed  for  the  leukocytes  present  in  the 
intestinal  wall,  the  evidence  seems  conclusive  that  this  claim  is 
without  substantial  foundation,  and  that  it  is  to  the  columnar 
epithelial  cells  covering  the  villi  that  the  change  is  to  be  attrib- 
uted. Up  to  the  present  time  the  form  of  proteid  into  which 
these  substances  are  changed  has  not  been  determined,  though  it 
is  doubtless  a  coagulable  proteid,  and  probably  serum-albumin 
or  globulin. 

Absorption  of  Vegetable  and  Animal  Proteids. — The 
products  of  vegetable  proteolysis  are  not  so  completely  absorbed 
as  are  those  of  animal  origin.  It  is  stated  by  Moore  that  this 
is  in  part  due  to  their  envelopes  of  indigestible  cellulose,  in  part 
to  their  shorter  stay  in  the  intestine  because  of  their  action  in 
causing  increased  peristalsis,  and  in  part  to  their  less  digestible 
character.  He  further  states  that  the  proteids  of  some  legumin- 
ous plants  and  cereals  are  absorbed  nearly  as  perfectly  as  those  of 
animal  origin,  while  in  most  others  (potato,  lentil)  it  is  much  less 
complete  (22  to  48  per  cent.  less).  The  percentage  of  the  nitrogen 
of  meat  or  egg  appearing  again  in  the  feces  in  man  amounts  to 
but  2.5  to  2.8  per  cent. ;  that  of  milk,  to  but  6  to  12  per  cent. 

Absorption  of  Fat. — There  is  no  dispute  as  to  the  lacteals 
being  the  channels  through  which  the  fat  reaches  the  blood-vascular 
circulation  by  way  of  the  thoracic  duct ;  the  presence  qf  fat  in 
the  vessels  has  been  observed  too  often  to  admit  of  any  doubt 
on  this  point.  Indeed,  it  is  the  milky  appearance  given  by  the 
fat-particles  to  the  contents  of  these  vessels  which  has  given  to 
them  the  name  of  lacteals  (Fig.  120),  but  as  to  the  manner  and 
form  in  which  fat  passes  into  the  villus  to  reach  the  lacteals  two 
theories  are  held  :  (1)  the  emulsion  theory  and  (2)  the  solution 
theory,  or,  more  correctly,  solution  theories. 

Emulsion  Theory. — This  theory  is  the  older,  and  explains  the 


262 


ABSORPTION  OF  THE  FOOD. 


absorption  of  fat  by  supposing  that  the  greater  part  of  it  is  emul- 
sified by  the  action  of  the  pancreatic  juice,  and,  being  thus  broken 
up  into  a  state  of  extremely  minute  subdivision,  the  particles  pass 
into  the  villi,  reach  the  lacteals,  and  by  way  of  the  thoracic  duct 
enter  the  blood-vascular  circulation,  in  this  theory  the  splitting 
up  of  the  fat  plays  the  important  part  of  aiding  in  the  emulsifying 
process  (p.  101).*  Although  fat-particles  have  often  been  observed 
in  the  interior  of  the  epithelial  cells,  they  have  never  been  seen 
in  the  striated  borders  of  these  cells,  which  is  a  remarkable  fact  if 
as  fat  they  pass  through  these  borders  to  reach  the  interior.  Nor 
is  there  any  special  reason  why  fat  should  be  taken  up  by  the 
columnar  epithelium  more  than  any  of  the  products  of  digestion. 
It  has  been  supposed  that  the  lymph-corpuscles,  already  described 
as  existing  between  the  epithelial  cells  of  the  villi,  put  out  pseudo- 
podia  and  take  in  the  fat-particles,  passing  them  on  through  the 
reticular  tissue  of  the  villi  (p.  223)  ;  but,  as  already  stated,  it  is 
in  the  columnar  epithelial  cells  that  the  fat  is  seen  during  the 


FIG.  140. — Longitudinal  section  through  summit  of  villus  from  human  small 
intestine;  X  900  (Flemming's  solution):  at  a  is  the  tissue  of  the  villus  axis;  b, 
epithelial  cells;  c,  goblet-cell;  d,  cutieular  zone  (Bohm  and  Davidoff). 

time  of  its  absorption,  and  these  are  entirely  distinct  from  the 
lymph-corpuscles. 


•  -• ' 

or 


ABSORPTION  OF  FAT.  263 

-v- 

Solution  Theories.— Of  these  there  are  two  :  (1)  the  soap  theory 
and  (2)  the  fatty-acid  theory. 

Soap  Theory. — This  theory  takes  cognizance  of  the  fact  that 
soaps  are  formed  in  the  small  intestine  by  the  action  of  steapsin 
on  the  neutral  fats,  by  which  they  are  split  up  into  fatty  acids 
and  glycerin,  the  fatty  acids  uniting  with  some  of  the  alkali  of 
the  intestinal  fluids/  with  the  result  of  forming  soluble  alkaline 
soaps.  The  theory'  under  consideration  supposes  that  these  soaps, 
together  with  the  glycerin,  are  absorbed  by  the  columnar  epithe- 
lium, and  that  when  within  the  protoplasm  the  acids  and  glycerin 
again  unite  by  virtue  of  cell-action  to  form  neutral  fat,  which  is 
seen  in  the  interior  of  the  cells.  We  have  already  referred  to  the 
fact  that  pancreatic  juice  has  the  power  of  decomposing  all  the 
fat  of  an  ordinary  meal  into  fatty  acids  and  glycerin  during  the 
time  that  it  remains  in  the  small  intestine.  The  objection  to  the 
soap  theory,  that  there  is  not  enough  alkali  in  the  body  to  com- 
bine with  the  fatty  acids  which  would  result  from  the  decomposi- 
tion of  the  fat  which  is  taken  in  as  food,  is  met  by  the  explanation 
that  only  a  small  amount  is  needed  at  a  given  time  to  form  a  soap, 
and  that  as  soon  as  the  soap  has  entered  the  cells  it  is  again  decom- 
posed into  fatty  acids  and  alkali,  the  latter  returning  to  the  blood 
and  being  again  available  for  use,  while  the  acids  unite  with  the 
glycerin  to  form  neutral  fat. 

'Fatty  Acid  Theory. — The  other  theory  is  that  fatty  acids,  formed 
in  the  manner  stated,  are  dissolved  by  the  bile,  and  in  this  form 
are  absorbed,  the  fatty  acids  uniting  with  the  glycerin  which  was 
absorbed  at  the  same  time  and  forming  neutral  fat.  There  is 
evidence  showing  that  when  fatty  acids  alone  are  absorbed,  glycerin 
is  formed,  probably  by  the  columnar  epithelium,  and  that  by  the 
union  of  the  two  neutral  fat  is  produced. 

The  evidence  seems  conclusive  that  fats  are  absorbed  as  soaps 
and  fatty  acids,  and  not  as  emulsified  fat,  the  fatty  acids  being 
dissolved  by  the  bile,  the  salts  and  pseudomucin  of  which  are  the 
efficient  factors  in  causing  this  solution. 

In  summing  up  this  portion  of  the  section  on  the  a  Chemistry 
of  the  Digestive  Processes,"  in  Schafer's  Text-Book  of  Physiology, 
Moore  says :  "It  is  probable,  then,  that  in  all  animals  a  great 
part  of  the  fat  is  absorbed  and  dissolved  in  the  form  of  soaps ; 
but  in  some  animals  a  part  is  also  absorbed  as  dissolved  fatty 
acids,  while  in  others  the  entire  quantity  leaves  the  intestine  in 
the  form  of  soaps." 

Course  of  Fat  from  Columnar  Epithelium  to  the  Lacteals. — 
Although  fat  is  not  absorbed  as  an  emulsion,  it  is  in  this  form  that 
it  exists  in  the  interior  of  the  epithelial  cells  after  its  re-formation 
from  the  fatty  acids  and  glycerin.  We  have  already  referred  to 
the  large  number  of  lymph-corpuscles,  or  leukocytes,  in  the  tissues 
composing  the  villi.  During  the  absorption  of  fat  these  cells 
contain  fat,  and  they  doubtless  carry  this  to  the  lacteals,  there 


264  ABSORPTION  OF  THE  FOOD. 

either  depositing  it  while  still  maintaining  their  integrity,  or  set- 
ting it  free  by  themselves  breaking  up  and  disintegrating.  Some 
authorities  hold  the  opinion  that  the  contractions  of  the  proto- 
plasm of  the  columnar  epithelial  cells  forces  out  the  fat,  and  that 
the  particles  pass  through  the  spaces  between  the  cells  and  thus 
reach  the  lacteals. 

Final  Disposition  of  the  Absorbed  Fat. — Inasmuch  as  no  more 
than  60  per  cent,  of  the  fat  absorbed  finds  its  way  into  the  thoracic 
duct,  it  might  be  inferred  that  the  lacteals  were  not  the  only 
channels  of  absorption,  and  that  the  capillary  blood-vessels  of  the 
villi  had  a  part  in  this  process,  but  there  is  no  more  fat  found  in 
the  blood  of  the  portal  vein  during  the  period  of  fat  absorption 
than  in  the  blood  of  the  rest  of  the  body,  and  even  this  is  not 
increased  if  the  contents  of  the  thoracic  duct  are  not  permitted 
to  enter  the  venous  circulation.  Just  what  becomes  of  the  40 
per  cent,  unaccounted  for  is  not  known.  It  was  long  regarded 
as  impossible  for  the  absorbed  fat  to  be  deposited  in  the  tissues 
unaltered,  and  it  was  supposed  that  it  all  underwent  such  changes  as 
to  destroy  its  integrity,  and  that  the  fat  which  existed  in  adipose 
tissue  and  elsewhere  was  entirely  a  new  formation.  In  reference 
to  this  Liebig  said  :  "  In  hay  or  the  other  fodder  of  oxen  no  beef- 
suet  exists,  and  no  hog's  lard  can  be  found  in  the  potato-refuse 
given  to  swine."  While  it  is  true  that  some  of  the  fat  of  the 
body  is  produced  from  other  substances  than  the  absorbed  fat, 
still,  the  evidence  is  conclusive  that  under  certain  circumstances 
this  is  deposited  in  the  tissues  without  undergoing  any  change 
whatsoever.  If  a  dog  is  starved  until  the  reserve  supply  of  fat 
has  been  exhausted,  and  it  is  then  fed  with  rape-seed  or  linseed 
oil  or  mutton  tallow,  fat  will  be  again  deposited  in  the  tissues 
and  in  it  some  of  the  fat  given  as  food  will  be  recognizable.  It 
is,  however,  a  question  whether  this  occurs  except  under  the 
exceptional  conditions  here  mentioned,  although  some  of  the  best 
authorities  state  that  the  fat  in  the  blood  after  a  meal  is  eventually 
stored  up  in  the  connective-tissue  cells  of  adipose  tissue.  Others 
claim  that  the  fat  of  the  food  is  completely  oxidized,  and  that 
the  body-fat  is  formed  from  proteids  or  carbohydrates,  or  both. 
The  probabilities  are  that  proteids  and  carbohydrates  are  the 
principal  sources  of  the  body-fat,  and  that  fat  itself  is  sometimes 
a  contributory  factor,  although  its  main  office  is  to  supply  the 
body  with  heat  or  other  form  of  energy. 

Absorption  by  the  I<arge  Intestine.— Although  destitute 
of  digestive  power,  this  portion  of  the  alimentary  canaUplays  an  im- 
portant part  in  the  process  of  absorption.  The  food  undergoes  diges- 
tion in  the  stomach  and  small  intestine,  staying  in  the  former  from 
one  and  a  half  to  five  hours,  and  in  the  latter  also  a  variable  time. 
In  one  case,  in  which  by  reason  of  the  existence  of  a  fistula  at  the 
end  of  the  small  intestine  it  was  possible  to  investigate  this  ques- 
tion^ it  was  found  that  food  began  to  enter  the  large  intestine  from 


QUANTITY  OF  FECES.  265 

two  to  five  and  a  quarter  hours  after  it  had  been  eaten,  and  that 
the  last  portions  did  not  reach  the  fistulous  opening  until  fr.om  nine 
to  twenty-three  hours  after  its  ingestion.  It  would  appear  that  in 
this  case  the  duration  of  gastric  and  intestinal  digestion  must 
have  been  very  brief — much  briefer  than  in  most  individuals. 

That  water  is  absorbed  by  the  walls  of  the  large  intestine  is 
conclusively  shown  by  the  fact  that  the  contents  of  the  small  in- 
testine when  they  pass  into  the  large  are  quite  liquid,  but  are 
ordinarily  relatively  solid  when  they  reach  the  lower  part  of  this 
portion  of  the.  intestine.  If  the  duration  of  the  stay  of  the  con- 
tents of  the  large  intestine  is,  as  stated,  twelve  hours,  the  time  is 
certainly  sufficient  for  important  changes.  There  are,  however, 
no  enzymes  formed  by  the  glands  of  the  mucous  membrane, 
but  the  evidence  is  overwhelming  that  proteids  are  here  readily 
absorbed.  This  power  possessed  by  the  large  intestine  is  made 
use  of  in  certain  diseases  of  the  stomach,  in  which  diseases  that 
organ  is  unable  to  perform  its  function,  when  by  means  of  nutrient 
enemata,  skilfully  administered,  life  may  be  maintained  for  a 
long  time.  In  a  case  of  circumscribed  peritonitis  from  perforated 
gastric  ulcer  a  female  patient  was  nourished  on  the  following  rectal 
enema  for  ninety-four  days,  during  which  time  she  lost  but  2700 
grams  in  weight : 

Lean  beef   . 300  grams ; 

Pancreas 150       " 

These  were  well  rubbed  up  in  a  mortar  and  strained,  and  then 
there  were  added  : 

Water q.  s. ; 

Carbonate  of  sodium 5  grams; 

Fresh  ox-gall 25       " 

This  sufficed  for  four  enemata  a  day  when  diluted  with  a  sufficient 
amount  of  tepid  water. 

There  is  evidence  that  sugar  and  fats  can  also  be  absorbed 
from  the  large  intestine. 


FECES  AND  DEFECATION. 

The  term  feces  is  applied  to  the  contents  of  the  large  intestine 
after  all  that  is  nutritious  has  been  absorbed.  As  these  pass  along 
this  portion  of  the  alimentary  canal  they  become  more  arid  more 
consistent  by  reason  of  the  absorption  of  the  water  until,  having 
been  reduced  to  a  mass  of  varying  consistency,  they  are  expelled 
from  the  rectum  in  the  act  of  defecation. 

Quantity  of  Feces. — The  amount  of  feces  daily  passed  by 


266  FECES  AND  DEFECATION. 

a  male  adult  varies  from  120  to  150  grams ;  this  may  be  increased 
to  500  grams,  if  the  diet  is  a  vegetable  one.  About  74  per  cent, 
of  feces  is  water. 

Color  of  Feces. — The  color  of  feces  is  very  much  affected 
by  substances  ingested.  Normally  it  may  be  called  brown,  due  to 
bile-coloring  matter,  or  to  hematin  derived  from  the  blood-color- 
ing matter  hemoglobin,  which  occurs  in  meat,  or  to  both.  Large 
quantities  of  bread  and  fat  give  to  the  feces  a  yellowish  color. 

Reaction  of  Feces. — The  statements  on  this  point  are  at 
variance,  and  indeed  the  reaction  is  not  always  the  same.  One 
authority  states  it  to  be  alkaline  on  the  surface,  due  to  contact 
with  the  mucous  membrane  of  the  intestine,  and  acid  in  the  inte- 
rior; another  regards  the  feces  as  having  an  alkaline  reaction 
ordinarily,  and  as  being  acid  exceptionally.  In  infants  they  are 
said  to  be  acid. 

Composition  of  Feces. — The  feces  contain  such  portions 
of  the  food  as  are  indigestible,  as  cellulose,  keratin,  and  chloro- 
phyl,  and  will  therefore  vary  in  composition  according  to  the 
composition  of  the  food.  In  addition  there  enter  into  its  composi- 
tion various  substances  derived  from  the  bile :  stercobilin,  which 
represents  all  that  remains  of  the  bile-pigments,  and  which  is  the 
same  as  urobilin,  and  hydrobilirubin ;  cholesterin,  ezcretin,  excre- 
toleic  acid,  indol,  skatol,  to  the  last  of  which  substances  the  fecal 
odor  is  principally  due  ;  volatile  fatty  acids,  calcium  or  magnesium 
soaps,  mucin,  ammonia,  sulphuretted  hydrogen,  carbon  dioxid, 
hydrogen,  nitrogen,  methan,  and  numbers  of  bacteria  (Fig.  141). 
These  gases  are  the  result  of  the  decomposition  of  the  proteids  by 
the  action  of  bile.  Besides  these,  the  feces  may  contain  the  pro- 
ducts of  the  excretory  action  of  the  epithelium  of  the  gastro-intes- 
tiual  canal  (p.  208). 

Meconium. — The  first  feces  which  are  evacuated  by  the 
infant  at  birth  are  termed  meconium.  This  is  dark  brownish 
green  in  color,  acid  in  reaction,  and  contains  mucin,  biliverdin, 
bilirubin,  bile-acids,  cholesterin,  fats,  fatty  acids,  and  the  phos- 
phates and  sulphates  of  calcium  and  magnesium. 

Defecation. — The  act  of  defecation  is  governed  by  the  ano- 
spinal  center.  The  mucous  membrane  and  muscular  coat  of  the 
rectum  are  supplied  with  nerves  from  the  several  plexuses  of 
spinal  nerves.  Feces  do  not  ordinarily  pass  into  the  rectum  until 
about  the  time  of  evacuation,  when  they  are  expelled  from  the 
sigmoid  flexure  into  the  rectum.  At  this  time  the  sphincter  ani 
is  in  a  state  of  contraction,  which  is  its  usual  condition,  kept  so 
by  the  impulses  that  come  from  the  spinal  cord.  This  contraction 
keeps  the  anus  closed  even  during  sleep,  and  is  entirely  inde- 
pendent of  the  action  of  the  brain ;  it  is  an  involuntary  act. 
When,  however,  feces  enter  the  rectum,  the  nerves  of  its  mucous 
membrane  become  stimulated,  and  impulses  are  conveyed  by 
afferent  nerves  to  the  anospinal  center  in  the  lumbar  enlargement 


DEFECATION. 


267 


of  the  cord,  and  from  this  impulses  are  reflected  which,  conveyed 
to  the  sphincter,  cause  its  relaxation.  Under  the  influence  of 
similar  impulses  which  pass  to  the  levator  ani  this/muscle  con- 
tracts and  draws  upward  the  edges  of  the  anus,  causing  it  to  open, 
while  at  the  same  time  the  muscular  fibers  of  the  rectum  contract 
and  expel  the  feces.  If  the  stimulation  is  very  pronounced,  the 
abdominal  muscles  may  also  be  called  into  action  irrespective  of 
the  will,  but  when  the  stimulus  is  slight  they  may  only  respond 
when  called  upon  by  the  brain.  The  connection  between  the  brain 
and  the  anospinal  center  is  very  close,  so  that  the  action  of  the 
latter  may  for  a  time  be  inhibited ;  but  if  the  rectum  becomes  very 
much  distended,  the  impulses  may  be  so  strong  that,  despite  the 
will,  defecation  will  take  place. 


FIG.  141.— Microscopic  c6nstituents  of  the  stools:  a,  vegetable  fragments;  6, 
muscular  fibers;  c,  white  blood-corpuscles;  d,  saccharomyces ;  e,  micro-organisms ; 
/,  crystals  of  triple  phosphate;  g,  fatty-acid  crystals  (partly  from  Jaksch). 


FIG.  142. — Monads  from  the  feces  :  a,  Trichomonas  intestinalis ;  6,  Cercomonas  in- 
testinalis;  c,  Ameba  coli;  d,  Paramcecium  coli ;  e,  living  monads;  /,  dead  monads 
(Jaksch). 

Involuntary  Discharges. — In  some  forms  of  disease  the  irrita- 
bility of  the  anospinal  center  is  so  great  that  when  the  rectum  is 
only  partially  filled  defecation  takes  place,  and  there  is  no  power 
to  retard  it.  Discharges  under  these  circumstances  are  said  to 
be  involuntary. 


268  THE  BLOOD. 

Involuntary  and  Unconscious  Discharges. — If  by  reason  of 
disease  or  of  injury  the  middle  or  the  upper  portions  of  the  cord 
become  so  disorganized  as  to  cut  off  communication  with  the 
brain,  while  at  the  same  time  the  lower  portion  is  in  normal  con- 
dition, the  act  of  defecation  takes  place  when  the  rectum  becomes 
sufficiently  distended  to  stimulate  the  anospinal  center  to  action  ; 
but  there  is  no  power  to  retard  nor  is  there  any  consciousness  of 
it,  since  the  connection  with  the  brain  is  severed.  Under  these 
circumstances  the  discharges  are  involuntary  and  unconscious. 
If  the  lumbar  portion  of  the  cord  is  the  seat  of  injury  or  of 
disease  to  such  an  extent  as  to  destroy  this  center,  the  sphincter  is 
permanently  relaxed,  and  the  feces  are  discharged  as  fast  as  they 
reach  the  anus. 

THE  BLOOD. 

The  office  of  the  blood  is  twofold  :  1.  It  carries  to  the  tissues 
of  the  body  the  materials  which  they  need  for  their  nourishment, 
and,  in  the  case  of  glands,  for  their  secretion;  and  2.  It  takes 
from  the  tissues  the  materials  which  result  from  their  destructive 
metabolism — waste  materials — which  it  carries  to  those  organs 
whose  function  it  is  to  eliminate  them,  as,  for  instance,  urea  to  the 
kidneys.  The  blood  may  be  likened  to  a  river  which  bears  to  the 
inhabitants  along  its  banks  their  daily  food,  and  into  which  at  the 
same  time  their  waste  is  discharged  and  carried  to  the  sea. 

Physical  Properties  of  Blood. — Blood  is  in  general  red  in 
color  and  alkaline  in  reaction  when  tested  with  litmus-paper,  and 
has  in  man  a  specific  gravity  of  about  ]  060,  although  this  varies 
in  men,  women,  and  children,  being  less  in  the  last,  except  at 
birth,  when  it  is  1066.  The  specific  gravity  of  the  corpuscles  is 
greater  than  that  of  the  plasma. 

Method  of  Obtaining  the  Specific  Gravity  of  Blood. — The  most 
convenient  method  is  that  of  Roy.  In  applying  it,  mixtures  of 
glycerin  and  water  are  made  of  different  specific  gravities,  and 
blood  is  dropped  into  these  until  one  is  found  in  which  the  drop 
of  blood  will  neither  rise  nor  sink.  Knowing  the  specific  gravity 
of  this  mixture,  that  of  the  blood,  being  the  same,  is  also  known. 

Color  of  Blood. — Although  blood  is  generally  said  to  be  red, 
still  this  color  is  subject  to  considerable  variation.  Thus,  venous 
blood  is  variously  described  as  bluish  red,  reddish  black,  deep 
purple,  dark  purplish  red,  dark  blue,  and  dark  purple,  while 
arterial  blood  is  a  bright  scarlet.  The  color  of  blood  depends  on 
hemoglobin  or  its  derivatives.  In  the  blood  of  an  animal  that 
has  been  suffocated,  where  the  purplish  or  blackish  color  is  most 
pronounced,  the  coloring-matter  is  almost  entirely  hemoglobin, 
while  in  arterial  blood  the  oxyhemoglobin  predominates,  and  in 
ordinary  venous  blood  there  is  a  mixture  of  hemoglobin  and  oxy- 
hemoglobin. 

When  the  coloring-matter  passes  out  from  the  corpuscles  into 


PHYSICAL  PROPERTIES  OF  BLOOD.  269 

the  fluid  portion  of  the  blood  the  blood  is  said  to  be  lakey.  This 
solution  of  the  hemoglobin  may  be  brought  about  in  many  ways, 
as  by  adding  distilled  water  or  a  solution  of  sodium  chlorid  or 
other  neutral  salt,  provided  that  the  solution  is  not  isotonic.  An 
isotonic  solution  is  one  in  which  the  amount  of  the  salt  present 
does  not  change  the  form  of  the  red  corpuscles  or  dissolve  out  its 
coloring-matter.  In  the  case  of  sodium  chlorid,  this  is  for  human 
blood  a  solution  having  a  percentage  of  0.9. 

Reaction  of  Blood. — The  alkalinity  of  blood  is  a  property  essen- 
tial to  life,  and,  so  far  as  the  plasma  is  concerned,  depends  upon 
the  presence  of  sodium  carbonate  and  phosphate.  The  alkalinity 
is  not  always  the  same ;  it  is  least  in  the  morning,  increases  in  the 
afternoon,  and  diminishes  at  night.  It  increases  during  digestion 
and  after  muscular  exercise.  It  is  said  that  the  blood  becomes 
acid  immediately  before  death  in  cases  of  cholera,  and  also  in  the 
condition  of  unconsciousness  called  coma,  which  occurs  sometimes 
in  diabetes. 

Odor  of  Blood. — Blood  has  an  odor  which  is  said  to  be  charac- 
teristic of  the  species  of  animal  from  which  it  is  taken.  The  odor 
is  usually  very  slight,  but  it  may  be  intensified  by  the  addition  of 
sulphuric  acid. 

Taste  of  Blood. — The  sodium  chlorid  which  blood  contains  gives 
to  it  a  salty  taste. 

Quantity  of  Blood. — The  amount  of  blood  in  the  body  of  a 
human  adult  is  about  7.7  per  cent.,  one-thirteenth  of  his  weight ; 
some  authorities  state  one-eighth,  and  others  one-fourteenth.  In 
a  newborn  child  it  is  about  one-nineteenth.  During  the  latter 
half  of  the  period  of  pregnancy  it  is  increased,  and  it  is  also  in- 
creased during  digestion. 

There  are  various  methods  of  determining  the  quantity  of 
blood  in  the  body ;  that  of  Welcker  is,  perhaps,  the  best  known. 
It  consists  in  opening  a  vein  of  an  animal  and  withdrawing  blood, 
which  is  measured  and  defibrinated.  This  is  then  divided  into 
portions,  each  of  which  is  diluted  with  a  different  amount  of 
water,  which  thus  gives  solutions  of  different  colors ;  these 
serve  subsequently  as  standards  of  comparison.  The  animal  is 
then  bled  until  all  the  blood  that  will  flow  has  been  withdrawn  ; 
this  is  defibrinated,  and  sufficient  salt  solution  is  injected  into  the 
vessels  to  wash  out  the  blood  that  remains.  This  is  continued 
until  the  fluid  comes  out  colorless.  The  body  is  then  cut  up  into 
small  pieces  and  mixed  with  saline  solution,  and  this  then  filtered, 
and  the  filtrate,  together  with  the  washings  of  the  blood-vessels,  is 
added  to  the  defibrinated  blood.  The  mixture  is  measured,  and 
diluted  with  water  until  its  color  corresponds  with  that  of  one  of 
the  standard  solutions,  when  the  calculation  can  be  made  which 
will  determine  the  total  amount  of  blood  in  the  body.  It  is 
necessary,  of  course,  to  include  the  quantity  of  blood  which  was 
first  withdrawn  to  make  the  standard  solutions. 


270 


THE  BLOOD. 


Temperature  of  Blood. — The  temperature  of  the  blood  varies 
greatly  in  the  different  parts  of  the  circulatory  apparatus.  The 
mean  temperature  may  be  stated  as  39°  C.;  that  of  the  superior 
vena  cava,  36.78°  C.;  the  right  side  of  the  heart,  38.8°  C.;  the 
left  side  of  the  heart,  38.6°  C.;  the  aorta,  38.7°  C.;  the  portal 
vein,  39.9°  C.;  the  hepatic  vein,  41.3°  C.  The  temperature  of 
the  blood  in  the  hepatic  vein  is  the  highest  in  the  body,  and  it 
varies  from  39.5°  C.  at  the  beginning  of  digestion  to  41.3°  C.  at 
the  time  when  the  process  is  most  active.  The  blood  in  the  right 
side  of  the  heart  is  made  warmer  by  its  proximity  to  the  liver, 
while  in  its  circulation  through  the  lungs  it  loses  heat,  and  is  there- 
fore cooler  in  the  left  side  of  the  heart.  In  the  portions  of  the 

body  exposed  to  the  air,  as  in 
the  skin,  the  temperature  of 
the  blood  may  be  doubtless  as 
low  as  36.5°  C. 

Distribution  of  Blood.— 
The  distribution  of  blood  in 
the  body  is  as  follows :  In  the 
heart,  lungs,  and  great  blood- 
vessels,  one-fourth;  in  the 
skeletal  muscles,  one-fourth ; 
in  the  liver,  one-fourth ;  in 
the  rest  of  the  body,  one- 
fourth. 

Microscopic  Structure 
Of  the  Blood.— When  ex- 
amined by  the  microscope  the 
blood  is  seen  to  be  composed 
of  corpuscles  suspended  in  a 
fluid,  the  plasma  or  liquor 
sanguinis. 

Blood- corpuscles. — By 
means   of  a    hematocrit   (Fig. 
143)   the   average   percentage 
of  corpuscles  in  human  blood 
FIG.  143.— Hematocrit.  has  been  found  to  be  about  48 

for  males,  and  43.3  for  females, 

while  for  children  of  from  six  to  thirteen  years  it  is  45.  In  mak- 
ing this  determination  the  blood  is  mixed  with  a  measured  quan- 
tity of  a  2J  per  cent,  solution  of  potassium  bichromate,  and  then 
placed  in  a  tube  which  is  revolved  very  rapidly,  or,  as  it  is 
expressed,  centrifugalized.  The  corpuscles  accumulate  at  the  bot- 
tom of  the  tube,  while  the  plasma  remains  above  them,  and  the 
volume  can  be  determined  by  simply  reading  the  scale. 

The  corpuscles  of  the  blood   are  of  three  varieties :  (1)  Red 
corpuscles  ;  (2)  colorless  corpuscles  ;  and  (3)  plaques. 

Red  corpuscles  in  human  blood  are  circular,  biconcave,  non- 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  271 

nucleated  disks,  having  an  average  diameter  of  7.7  //,  some  of 
them  being  as  small  as  4.5  p.,  while  others  are  9  JJL.  The  small 
corpuscles  are  termed  microcytes,  and  are  regarded  as  not  fully  de- 
veloped corpuscles.  In  chronic  anemic  conditions  some  have  been 
found  as  large  as  14  //,  and  others  as  small  as  2.2  p. 

Number  of  Red  Corpuscles. — The  number  of  red  corpuscles  in 
a  cubic  millimeter  of  the  blood  of  a  male  adult  has  been  reckoned 
at  5,000,000  ;  in  that  of  a  female,  4,500,000.  In  a  man  weighing 
68  kilos  there  are  estimated  to  be  25,000,000,000,000,  present- 
ing a  superficial  area  of  about  3200  square  meters.  In  all  the 
blood  of  the  body  in  health  their  number  is  consequently  enormous. 

There  are  various  methods  of  determining  the  number  of  red 
corpuscles:  (1)  By  the  hematocrit  (p.  270);  (2)  by  the  hemacy- 
tometer. 

By  the  Hematocrit. — This  instrument  has  been  described,  and 
its  use  explained,  for  determining  the  relative  proportion  of  cor- 
puscles and  plasma.  It  has  been  ascertained  that  each  volume  of 
corpuscles,  as  indicated  by  the  scale,  represents  97,000  corpuscles. 


FIG.  144. — Blood-corpuscles :  a,  blood-plaques  or  third  corpuscles ;  6,  red  corpuscles ; 
c,  white  corpuscles  (Eberth  and  Schimmelbusch). 

By  the  Hemacytometer. — There  are  three  forms  of  this  instru- 
ment— that  of  Gowers,  that  of  Thorna-Zeiss,  and  that  of  Oliver. 

Gowers'  hemacytometer  consists  of  a  pipet,  which  contains 
995  cu.mm.  when  filled  to  the  mark  made  on  the  tube,  a 
glass  mouthpiece  is  connected  with  this  pipet  by  means  of 
rubber  tubing ;  a  capillary  tube,  holding  5  cu.mm.  when  filled 
to  the  mark,  this  also  having  a  mouthpiece  and  rubber  tubing ;  a 
brass  plate,  with  a  glass  slide,  on  which  is  a  cell  having  a 
de£>th  of  1-  mm.  and  divided  on  the  bottom  into  y1^  mm.  squares, 
the  cell  in  use  being  covered  by  a  cover-glass ;  a  jar,  in  which 
the  blood  to  be  examined  is  diluted  ;  a  glass  rod,  for  staining ; 
and  a  needle,  for  pricking  the  finger  to  obtain  blood. 

A  solution  of  sodium  sulphate  is  made  having  a  specific  gravity 
of  1025,  which  corresponds  to  the  specific  gravity  of  blood-plasma, 
and  this  is  sucked  up  into  the  pipet  to  the  mark  indicating 
995  cu.mm.  This  is  then  deposited  in  the  jar.  The  finger  is 
pricked  with  the  needle,  the  amount  of  projection  of  which  can  be 
regulated  by  a  screw,  and  5  cu.mm.  of  blood  sucked  up  into  the 
capillary  tube,  and  this  is  then  deposited  in  the  jar  with  the  saline 
solution,  and  the  mixture  thoroughly  stirred  with  the  glass  rod. 
A  drop  of  the  mixture  is  then  placed  in  the  cell  and  a  cover-glass 


272 


THE  BLOOD. 


placed  over  it.  The  brass  plate  is  placed  on  the  microscope,  with 
a  magnifying  power  of  400  diameters.  In  a  short  time  the  red 
corpuscles  settle  to  the  bottom  of  the  cell,  and  the  number  con- 


S 


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o 


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o 


o  o 


o 


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D 


O 


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0 


FIG.  145.— Thoma-Zeiss  hemacytometer.  1.  Mixing  apparatus:  a,  capillary 
tube  in  which  the  blood  is  taken ;  6,  chamber  for  mixing  the  blood  with  the 
diluting  solution ;  c,  glass  ball  to  aid  in  mixing  the  blood  with  the  diluting  solu- 
tion. 2.  Cross-section  of  the  chamber  in  which  the  blood  is  counted.  3.  Section 
of  the  field  on  which  the  blood  is  counted,  showing  thirty-six  squares. 

tained  in  10  squares  are  counted,  added  together,  and  multiplied 
by  10,000;  the  product  is  the  number  in  1  cu.mm.  of  blood. 

Thoma-Zeiss  Hemacytometer  (Fig.  145). — This  is  quite  simple 
to  use,  inasmuch  as  the  blood  is  drawn  and  diluted  in  one  in- 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  273 

strument.  It  consists  of  a  pipet  with  mouthpiece  and  tubing 
connecting  the  two.  It  is  carefully  graduated,  and  has  a  bulb 
which  contains  100  times  as  much  as  the  capillary  tube  when 
filled  to  mark  1.  In  this  bulb  is  a  glass  bulb  which  aids  in  the 
mixing  of  the  blood  and  saline  solution.  There  is  also  a  glass 
slide  (Fig.  145,  2)  having  a  covered  disk.  On  the  surface  of  this 
1  cu.mm.  is  divided  into  400  squares,  each  -fa  mm.  This  is 
surrounded  by  a  cell  of  such  height  that  when  a  cover-glass  is 
placed  upon  it  its  under  surface  will  be  -fa  mm.  above  the  disk.  The 
linger  being  pricked,  the  blood  is  drawn  into  the  capillary  tube  as  far 
as  1  on  the  scale  ;  the  saline  solution,  Hay  em's  fluid  (see  below)  or 
3  per  cent,  sodium  chlorid  solution,  is  then  drawn  up  to  101.  The 
pipet  is  then  shaken  so  as  to  mix  the  blood  and  solution  thoroughly, 
and  a  drop  of  the  mixture  placed  on  ra  and  covered  with  a  cover- 
glass.  The  volume  of  blood  above  each  of  the  squares  will  be  ffa^ 
cu.mm.  The  corpuscles  in  from  10  to  20  squares  are  counted,  and  by 
dividing  this  number  by  the  number  of  squares  taken,  the  average 
per  square  will  be  obtained.  This  multiplied  by  4000  X  100 
equals  the  number  of  corpuscles  in  a  cubic  millimeter  of  blood. 
For  the  depth  of  the  cell  being  -fa  mm.,  and  the  area  of  each 
square  being  j^-0-  sq.mm.,  the  volume  of  blood  on  each  square 
would  be  ffaq  cu.mm.  Inasmuch  as  the  blood  has  been  diluted 
100  times,  1  cu.mm.  of  blood  withdrawn  from  the  vessels 
would  contain  400,000  times  the  corpuscles  in  1  square. 

Hayem's  fluid  consists  cf  sulphate  of  sodium,  5  grams  ;  sodium 
chlorid,  1  gram  ;  corrosive  sublimate,  0.5  gram ;  dissolved  in  200 
c.c.  of  distilled  water. 

Oliver's  Hemacytometer  (Fig.  146). — This  apparatus  consists 
of  a  measuring  pipet,  a  ;  a  dropper,  b  ;  a  mixing  tube,  c.  A  small 
amount  of  blood  is  measured  in  the  measuring  pipet  and  mixed  in 
the  mixing  tube  with  Hayem's  fluid.  The  tube  is  then  held 
between  the  fingers,  and  the  light  of  a  wax  candle,  held  about  2^- 
meters  from  the  eye,  in  a  dark  room,  is  looked  at,  the  tube  being 
held  edgeways.  Enough  fluid  is  added  to  make  the  flame  appear 
as  a  bright  line  through  the  mixture.  If  the  red  corpuscles  are 
present  to  the  number  of  5,000,000  to  the  cubic  millimeter,  the 
surface  of  the  mixture  will  stand  at  100.  If  the  number  is  less, 
it  will  not  require  so  much  of  the  fluid  to  make  the  mixture  trans- 
parent ;  while  if  the  number  is  in  excess  of  normal  it  will  require 
more.  The  graduations  on  the  tube  are  percentages  of  the  normal 
standard;  thus  if  100  represents  5,000,000  corpuscles,  80  would 
represent  4,000,000. 

Many  observations  have  shown  that  the  number  of  red  corpus- 
cles is  subject  to  considerable  variation  even  in  the  same  individual. 
Muscular  exercise,  and  even  massage,  which  is  passive  exercise, 
increase  the  number ;  while  food  diminishes  it. 

The  blood  of  persons  living  in  high  altitudes  has  shown  the 

18 


274 


THE  BLOOD. 


presence  of  red  corpuscles  to  the  number  of  8,000,000  per 
cu.mm.  It  does  not  necessarily  follow,  however,  that  this  is  an 
absolute  increase,  for  it  may  be  due  to  loss  of  the  water  of  the  blood, 
caused  by  increased  evaporation  from  the  body,  and  to  increased 


FIG.  146.— Oliver's  hemacy tometer :  a,  measuring  pipet:  6,  dropper  to  contain 
Hayem's  fluid;  c,  mixing  tube  graduated  in  percentages;  d,  mode  of  making  the 
observation  (this  must  be  done  in  a  dark  room) ;  a,  b,  and  c  are  natural  size. 

arterial  tension,  by  which  the  amount  of  lymph  is  increased.  In 
conditions  of  apparent  health  so  small  a  number  as  1,600,000  has 
been  found.  In  newborn  children,  5,000,000  per  cu.mm.  have 
been  estimated. 

Color   of   the   Red    Corpuscles. — A    single   corpuscle    is  of  a 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  275 

yellowish  or  amber  color,  and  the  red  color  of  the  blood  appears 
only  when  the  corpuscles  are  in  thick  layers  or  in  masses. 

^Structure  of  Red  Corpuscles. — There  is  a  difference  of  opinion 
among  histologists  as  to  the  minute  structure  of  these  bodies. 
Schafer  describes  it  as  follows :  "  Each  red  corpuscle  is  formed 
of  two  parts,  a  colored  and  a  colorless,  the  former  being  a  solution 
of  hemoglobin ;  the  latter,  the  so-called  stroma,  which  is  by  far 
the  smaller  quantity,  being  composed  of  various  substances,  chief 
among  these  being  lecithin  and  cholesterin,  together  with  a  small 
amount  of  cell-globulin."  According  to  this  view,  the  colorless 
stroma  serves  as  an  envelope  to  contain  the  hemoglobin  in  solution. 

By  other  authorities,  of  whom  Rollett  may  be  regarded  as  an 
exponent,  the  entire  corpuscle  is  made  up  of  an  elastic  structure, 
the  stroma,  the  outer  portion  of  which  is  denser  than  the  inner, 
and  having  in  its  interstices  the  coloring- matter  together  with 
lecithin,  cholesterin,  and  globulin. 

In  discussing  this  subject,  Gamgee,  in  Schafer's  Text-Book  of 
Physiology,  says :  "  Without  attempting  to  speculate  beyond  the 
facts  which  we  possess,  it  may,  however,  be  assumed  that  hemo- 
globin exists  in  the  blood-corpuscles  in  the  form  of  a  compound 
with  a  yet  unknown  constituent  of  the  corpuscle.  This  compound, 
the  existence  of  which  we  are  forced  to  assume,  is  characterized  by 
remarkable  instability,  for  it  is  decomposed,  setting  free  the  hemo- 
globin, which  then  passes  into  solution  (1)  when  the  blood-plasma 
or  serum,  in  which  the  corpuscles  are  suspended,  is  diluted;  (2) 
when  certain  substances  act  upon  the  corpuscles  (ether,  chloro- 
form, salts  of  the  bile-acids,  certain  products  of  putrefaction) ; 
(3)  by  the  action  of  heat,  by  alternate  freezing  and  thawing,  by 
induction  shocks,  etc." 

The  red  corpuscles  are  exceedingly  flexible,  as  may  readily  be 
seen  by  watching  them  in  the  circulation  of  the  web  of  a  frog's 
foot.  At  times  they  will  be  so  stretched  out  as  to  pass  through  a 
vessel  whose  diameter  is -smaller  than  is  theirs  when  in  a  circular 
shape ;  or  sometimes  they  may  be  seen  bent  over  the  projection 
made  by  the  junction  of  two  vessels,  one  portion  being  within 
each,  until,  one  current  being  the  stronger,  they  are  carried  for- 
ward by  it,  resuming  their  circular  shape  as  soon  as  the  size  of 
the  vessel  permits. 

The  human  red  corpuscles  possess  in  adult  life  no  nuclei.  This 
is  true  of  all  mammals.  Up  to  the  fourth  month  of  fetal  life  the 
blood  of  the  human  embryo  contains  nucleated  red  corpuscles.  It 
is  uncertain,  however,  whether  these  develop  into  the  non-nucleated 
forms.  In  other  vertebrates  the  corpuscles  are  nucleated. 

Chemical  Composition  of  Red  Corpuscles. — An  analysis  of  the 
red  corpuscles  of  human  blood  shows  the  presence  of  both  organic 
and  inorganic  compounds.  The  percentage  of  organic  ingredients 
in  dried  human  corpuscles  in  one  analysis  was  as  follows  :  Proteids 


276  THE  BLOOD. 

and  nuclein,  12.24  ;  hemoglobin,  86.79  ;  lecithin,  0.72  ;  cholesterin, 
0.25.  The  nucleoproteid  is  called  by  some  writers  cell-globulin. 
The  inorganic  substances  are  potassium  and  sodium  salts ;  potas- 
sium constituting  40.89  per  cent,  of  the  total  ash,  while  of  sodium 
there  is  only  9.71  per  cent. 

Hemoglobin. — This  is  the  term  applied  to  the  highly  complex, 
iron-containing,  crystalline  coloring-matter,  which  forms  the  most 
important  constituent  of  the  colored  corpuscles  of  the  blood,  and 
by  virtue  of  which  they  perform  their  function  as  the  oxygen- 
carriers  of  the  organism  (Gamgee).  It  constitutes  95  per  cent,  of 
the  solid  matter  of  the  red  corpuscles,  and  in  the  adult  male  there 
are  about  14  grams  for  each  100  grams  of  blood,  or  in  all  about 
750  grams.  When  united  with  a  molecule  of  oxygen  it  forms 
oxyhemoglobin  ;  when  it  exists  by  itself,  without  this  molecule,  it 
bears  the  name  of  hemoglobin  or  reduced  hemoglobin.  Because  of 
its  property  of  serving  as  an  oxygen-carrier  it  is  spoken  of  as  a 
respiratory  pigment.  The  hemoglobin  in  the  blood  of  different 
animals  varies  both  physically  and  chemically,  so  that  some  writers 
speak  of  the  hemoglobins;  but  Gamgee  thinks  this  is  unnecessary 
and  misleading,  inasmuch  as  the  proportion  in  which  iron,  the 
characteristic  element  in  the  blood  coloring-matter,  occurs,  is 
absolutely  the  same  in  many  animals ;  and,  besides,  there  is  abun- 
dant evidence  in  favor  of  the  view  that  the  optical  and  physiologic 
properties  of  hemoglobin  depend  upon  the  identical  "  typical 
nucleus"  in  all  animals. 

When  hemoglobin  is  decomposed  in  the  presence  of  oxygen, 
it  breaks  up  into  a  proteid,  globulin,  which  constitutes  96  per 
cent,  of  it,  and  hematin,  of  which  there  is  4  per  cent.  If  this 
decomposition  takes  place  without  oxygen,  instead  of  hematin, 
hemochromogen  re  produced.  It  is  to  this  latter  substance  that 
hemoglobin  owes  its  characteristic  property  of  taking  up  oxygen. 

The  exact  percentage-composition  of  the  hemoglobin  of  human 
blood  has  not  been  determined ;  that  of  the  dog,  as  analyzed  by 
Jaquet,  is  as  follows :  C,  53.91  ;  H,  6.62 ;  N,  15.98;  8,0.542; 
FeO,  0.333  ;  O,  22.62.  The  molecular  formula  is  C758H1203N195- 
833,  FeO218,  making  the  molecular  weight  16.669.  Gamgee  has 
calculated  for  the  hemoglobin  of  the  ox  the  following :  C759H1208- 
N2loS2FeO204.  Bunge  says,  in  reference  to  the  molecular  weight 
of  hemoglobin  :  "  The  enormous  size  of  the  hemoglobin-molecule 
finds  a  teleological  explanation,  if  we  consider  that  iron  is  eight 
times  as  heavy  as  water.  A  compound  of  iron  which  would  float 
easily  along  with  the  blood-current  through  the  vessels  could  only 
be  secured  by  the  iron  being  taken  up  by  so  large  an  organic 
molecule."  Hemoglobin  forms  crystals  in  the  absence  of  oxygen. 

Hemoglobinometers. — There  have  been  various  methods  devised 
to  determine  the  amount  of  hemoglobin  in  the  blood.  Those  which 
are  commonly  used  are  sufficiently  exact  for  clinical  purposes, 


MICROSCOPIC  STRUCTURE  OF  THE  -BLOOD. 


277 


though  undoubtedly  the  determination  of  the  amount  of  iron 
would  give  more  precise  results;  the  ordinary  methods  depend 
upon  the  color. 


1 


a* 

FIG.  147. — Oliver's  hemoglobinometer :  e,  glass  cell  for  receiving  the  blood  from 
the  pipet  (the  dilution  is  effected  within  the  cell  itself) ;  a,  standard  graduations 
made  of  tinted  glass.  To  avoid  multiplying  these  unduly,  they  are  furnished  in 
tens  per  cent.,  the  intermediate  divisions  of  the  scale  being  obtained  by  superposing 
tinted  glass  riders  in  a  graduated  series  from  1  to  9.  (These  riders  are  not  repre- 
sented in  the  figure.)  The  apparatus  is  shown  of  the  natural  size. 

Oliver's  Hemoglobinometer  (Fig.  147). — Some  of  the  blood,  the 
amount  of  whose  hemoglobin  is  to  be  determined,  is  diluted 
and  placed  in  the  glass  cell  e ;  the  color  of  this  diluted  blood  is 
then  compared  with  the  series  of  tinted  glasses,  the  color  of  each 


278 


THE  BLOOD. 


of  which  corresponds  to  a  known  percentage  of  hemoglobin. 
The  one  that  corresponds  to  the  color  of  the  sample  of  blood 
determines  the  percentage  of  hemoglobin  in  the  blood  under  ex- 
amination. 

Goners'  Hemoglobinometer  (Fig.  148).— This  apparatus  consists 
of  two  glass  tubes  having  the  same  diameter,  d  contains  glycerin- 
jelly  colored  with  carmine,  so  that  the  color  represents  that  of 
blood  diluted  one  hundred  times  with  water.  The  finger  is  pricked 
with  the  needle/,  and  the  blood  is  sucked  up  into  the  pipet  b  to 
the  20  cu.mm.  mark,  and  then  blown  out  into  the  tube  c,  distilled 
water  being  added  in  drops  from  a  until  the  color  of  the  diluted 
blood  corresponds  with  the  color  in  d.  The  tube  c  is  so  graduated 
that  when  filled  to  100  with  diluted  blood  its  color  corresponds  to 


FIG.  148. — Gowers'  hemoglobinometer :  a,  pipet  bottle  for  distilled  water;  b, 
capillary  pipet ;  c,  graduated  tube ;  d,  tube  with  standard  dilution ;  /,  lancet  for 
pricking  the  finger. 

that  of  d,  which  would  consequently  represent  the  color  of  normal 
blood.  If,  therefore,  in  order  to  produce  a  color  corresponding  to 
that  in  d,  water  must  be  added  to  fill  the  tube  to  a  higher  level 
than  100,  the  hemoglobin  is  above  normal ;  while  if,  on  the  other 
hand,  the  color  is  produced  below  100,  then  the  graduation  at 
that  point  represents  the  percentage  of  the  normal.  Thus  if  at 
75  the  corresponding  color  is  reached,  only  75  per  cent,  of  the 
normal  amount  is  present. 

Von  FleischVs  Hemometer  (Fig.  149). — This  consists  of  a  stand 
carrying  a  white  reflecting  surface,  e,  and  having  a  platform  below 
upon  which  slides  a  glass  wedge  colored  red,  6.  On  the  platform 
is  a  compartment,  J,  divided  into  two  by  a  vertical  partition.  The 
one  which  is  directly  above  the  colored  wedge  is  filled  with  distilled 
water.  Into  the  other,  a  small  amount  of  distilled  water  is  placed. 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD. 


279 


The  finger  is  pricked  and  the  blood  which  is  to  be  examined  is 
drawn  up  into  a  tube  provided  for  that  purpose.  The  blood  is 
then  put  into  the  second  compartment,  which  is  afterward  filled 
with  distilled  water.  The  milled  head /is  then  turned,  and  this 
carries  along  with  it  the  wedge  of  glass.  Wnen  tne  colors,  as 
seen  by  transmitted  artificial  light,  in  the  contents  of  both  com- 
partments correspond,  the  percentage  of  hemoglobin  in  the  blood 


FIG.  149. — Von  Fleischl's  hemometer:  a,  stand;.  6,  narrow  wedge-shaped  piece 
of  colored  glass  fitted  into  a  frame  (c),  which  passes  under  the  chamber  ;  d,  hollow 
metal  cylinder,  divided  into  two  compartments,  which  hold  the  blood  and  water ; 
e,  white  plate  from  which  the  light  is  reflected  through  the  chamber;  /,  screw 
by  which  the  frame  containing  the  colored  glass  is  moved  ;  g,  capillary  tube  to 
collect  the  blood ;  h,  pipet  for  adding  the  water ;  i,  opening  through  which  may 
be  seen  the  scale  indicating  percentage  of  hemoglobin. 

may  be  ascertained  by  reading  the  scale  at  i.     This  instrument 
should  be  used  in  a  dark  room. 

Oxy hemoglobin. — It  is«  this  substance  which  gives  to  arterial 
blood  the  scarlet  color  which  is  so  characteristic  of  it ;  here,  how- 
ever, it  occurs,  not  by  itself,  but  together  with  hemoglobin  (re- 
duced hemoglobin)  and  in  excess  of  the  latter.  In  venous  blood 
the  two  also  coexist,  but  the  hemoglobin  is  in  excess,  while  in 
the  blood  of  asphyxia  the  coloring-matter  is  almost  entirely 
hemoglobin. 


280 


THE  BLOOD. 


The  hemoglobin  of  some  animals,  as  the  guinea-pig,  cat,  and 
dog,  crystallizes  very  readily,  while  that  of  man,  and  the  mammal? 
generally,  forms  crystals  with  more  difficulty.  To  obtain  crystals  of 
oxyhemoglobin,  the  blood  should  be  mixed  in  a  test-tube  with  one- 
sixteenth  its  volume  of  ether  and  the  tube  shaken  with  consid- 
erable force.  The  coloring-matter  passes  into  the  plasma,  and  the 
blood  becomes  lakey.  If  the  tube  is  then  placed  on  ice,  in  a  short 
time  the  crystals  will  form  and  can  be  examined  under  the  micro- 
scope. The  form  of  the  crys- 
tals varies  in  different  animals 
(Fig.  1 50).  In  the  guinea-pig, 
the  blood  of  which  is  easily 
obtained,  and  whose  oxyhe- 
moglobin crystallizes  readily, 
they  are  rhombic  tetrahedra. 
Derivatives  of  Hemoglobin. 
— Besides  oxyhemoglobin,  the 
properties  of  which  have  al- 

w    1    ^     %  ready  been  given,  there  are 

jP        \jfyl  -  0y      various  derivatives  of  hemo- 

MJi/       A^^^^  *      globin  ;  among  them  are  the 
^^^|  ^Br^      ^^^1^^       following : 

T^E^^c  Carbon-monoxid  Hemoglo- 

^^^-^^  bin. — As    one    molecule    of 

^5^  A  hemoglobin    combined    with 

/j^  one  of  oxygen  forms  oxyhem- 

f  oglobin,  so  one  molecule  of 

hemoglobin  united  with  one 
of  carbon  monoxid  forms 
Carbon-monoxid  hemoglobin. 
There  is,  however,  one  strik- 
ing difference  in  the  two  com- 
binations. In  the  former  the 
oxygen  is  readily  displaceable, 
while  in  the  latter  the  com- 
pound is  a  very  stable  one, 
although  Gamgee  has  shown 
that  by  the  long-continued  passage  of  neutral  gases  through  solu- 
tions of  CO-hemoglobin  the  CO  is  gradually  driven  out,  and  reduced 
hemoglobin  is  obtained.  Carbon  monoxid  is  the  gas  formed  when 
combustion  is  incomplete,  such  as  is  produced  by  the  charcoal  fur- 
nace used  in  France  for  suicidal  purposes  ;  the  charcoal  fumes  when 
inhaled  in  sufficient  quantity  produce  fatal  results.  It  is  also  a  con- 
stituent of  illuminating-gas,  where  it  exists  in  proportions  ranging 
from  7.9  to  28.25  per  cent.,  and  is  not  infrequently  the  cause  of 
death.  The  gas  displaces  the  oxygen  and  unites  so  firmly  with  the 
hemoglobin  that  even  with  artificial  respiration  it  cannot  be  dis- 


FIG.  150.— Crystallized  hemoglobin:  a,  b, 
crystals  from  venous  blood  of  man ;  c,  from 
the  blood  of  a  cat ;  rf,  from  the  blood  of  a 
guinea-pig  ;  e,  from  the  blood  of  a  hamster ; 
/,  from  the  blood  of  a  squirrel  (after  Frey). 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  281 

placed.  The  color  of  carbon-monoxid  hemoglobin  is  a  cherry  red, 
and  the  blood  in  persons  poisoned  with  it  has  this  color. 

Nitric-oxid  Hemoglobin. — Nitric  oxid  will  also  displace  the 
oxygen  from  oxyhemoglobin,  and  the  nitric-oxid  hemoglobin  which 
results  is  a  more  stable  compound  than  carbon-monoxid  hemo- 
globin. It  consists  of  one  molecule  of  hemoglobin  and  one  of 
nitric  oxid. 

Carbo-hemoglobin. — Hemoglobin  will  also  unite  with  carbon 
dioxid,  and  it  has  been  demonstrated  that  each  gas  acts  with  refer- 
ence to  hemoglobin  independently  of  the  others — i.  e.,  that  even 
when  a  solution  of  hemoglobin  is  nearly  saturated  with  oxygen,  it 
can  still  take  up  as  much  carbon  dioxid  as  when  no  oxygen  is 
present.  It  has  been  suggested  that  the  explanation  of  this  is  that 
the  oxygen  unites  with  the  portion  which  gives  the  color,  hemochro- 
mogen,  and  the  CO2  with  the  proteid  portion. 

Methemoglobin. — This  is  regarded  as  being  chemically  the  same 
as  oxyhemoglobin,  except  that  the  union  of  the  hemoglobin  and 
oxygen  is  more  stable.  Oxyhemoglobin  may  be  converted  into 
methemoglobin  by  the  action  of  many  substances,  among  which 
may  be  mentioned  potassium  ferricyanid,  nitrites,  potassium 
permanganate,  etc.  It  has  been  demonstrated  that  when  this  con- 
version takes  place  the  whole  of  its  oxygen  passes  into  such  inti- 
mate relationship  with  the  hemoglobin  that  it  cannot  be  displaced 
by  carbon  monoxid.  Methemoglobin  also  crystallizes,  the  form  of 
the  crystals  being  the  same  as  that  of  oxyhemoglobin.  Methemo- 
globin is  the  form  in  which  the  blood-coloring  matter  exists  when 
blood  has  been  for  a  considerable  time  exposed  to  the  air.  Jt  is 
also  known  as  reduced  hematin. 

Hematin. — Various  formulae  have  been  given  to  represent  this 
substance.  That  of  Hoppe-Seyler  is  C^H^^FeOg.  When  oxy- 
hemoglobin is  decomposed  by  acids  or  alkalies  in  the  presence  of 
oxygen  hematin  results. 

Hemin. — This  is  chemically  hematin  hydrochlorid,  C34H^5N4- 
FeO5HCl.  If  to  a  drop  of  blood  on  a  glass  microscopic  slide  is 
added  a  drop  or  two  of  glacial  acetic  acid  and  the  mixture  is  boiled, 
after  evaporation  there  will  be  found,  if  examined  by  the  micro- 
scope, brownish  prismatic  crystals  of  hemin.  These  were  discovered 
'by  Teichmann,  and  are  also  known  by  his  name  (Fig.  151).  These 
crystals  are  so  characteristic  that  this  method  of  producing  them 
is  very  much  used  to  determine  whether  colored  spots  or  stains 
are  blood  or  not.  The  explanation  of  the  changes  which  take 
place  is  as  follows :  The  hemoglobin  is  decomposed  by  the  action 
of  the  acetic  acid  into  hematin  and  a  proteid  ;  and  at  the  same 
time  the  sodium  chlorid  is  decomposed,  and  the  hydrochloric  acid 
which  is  set  free  unites  with  the  hematin.  If  this  test  is  used  in 
the  case  of  old  blood-stains,  from  which  the  sodium  chlorid  may 


282  THE  BLOOD. 

have  been  washed  out,  it  is  necessary  to  add  a  small  crystal  of  the 
salt  to  the  acid  before  boiling. 

Hemochromoyen. — This  is  also  called  reduced  hematin,  and  re- 
sults when  hemoglobin  is  decomposed  by  alkalies,  or  acids,  in  the 
absence  of  all  oxygen.  Its  crystallizability  has  not  been  demon- 
strated. Gamgee  questions  whether  hemochromogen  exists  pre- 
formed in  hemoglobin  and  its  compounds. 

Hematoporphyrin. — If  to  hematin  strong  sulphuric  acid  is 
added,  the  iron  is  dissolved  out,  making  ferrous  sulphate,  and 
hematoporphyrin  or  iron-free  hematin  re- 
mains. It  is  regarded  by  some  as  iso- 
meric  with  bilirubin.  The  formula  as 
given  by  Hoppe-Seyler  is  C34H3gN4O6.  It 
has  in  acidulated  alcoholic  solutions  a  pur- 
ple color,  assuming  a  bluish-violet  tint  when 
made  strongly  acid;  but  alkaline  solutions 

\are  red.     Solutions  of  this  substance  "  ex- 
^g^gg-J8*8*'  hibit  a  magnificent  fluorescence  "  (Gamgee). 

It  is  found  in  small  amount  in  normal  urine, 
FIG.  151.  —  Hemiu,    or     and  in  large  quantity  in  chronic  poisoning 

Teichmann's  crystals,  from      from  t]ie  uge  Qf  gulphonal. 

blood-stains     on    a    cloth  TT         .    .  -,.          TIT       iij  i 

(Huber).  Hematoiain. — In     blood-clots,   such    a^ 

form  in  apoplexy,  where  a  blood-vessel 

of  the  brain  ruptures,  a  crystalline  substance  is  found,  to  which 
Virchow  gave  the  n|ime  hematoidin.  It  is  beyond  question  a  deriv- 
ative of  hemoglobin.  Its  formula  is  given  as  C16H18N2O3,  and  it 
is  identical  with  bilirubin. 

Histohematins. — In  the  muscles  and  other  tissues  of  the  body 
coloring-matters  are  found  which  are  called  histohematins,  which 
may  be  related  to  hemoglobin,  but  the  relationship  has  not  as  yet 
been  established. 

Spectra  of  Hemoglobin  and  its  Derivatives. — Before  discussing 
the  spectra  of  hemoglobin  and  its  derivatives,  it  will  not  be  inap- 
propriate to  describe  the  spectroscope  and  its  application  to  the 
differentiation  of  the  coloring-matters  of  the  blood  in  the  varied 
forms  in  which  we  have  found  them  to  occur.  For  a  more  de- 
tailed description  of  spectrum  analysis  our  readers  are  referred  to 
the  many  excellent  treatises  on  physics.  The  wonderful  adapta-* 
bility  of  spectrum  analysis  to  the  solution  of  many  physiologic 
problems  may  be  illustrated  by  the  statement  that  by  its  means 
31700000  °f  a  milligram  of  sodium  can  be  detected,  and  a  corre- 
sponding delicacy  of  analysis  is  true  of  other  substances  ;  thus  the 
rapid  absorption  and  diffusion  of  certain  substances  have  been  de- 
termined by  the  spectroscope.  Roscoe,  in  his  Spectrum  Analysis, 
states  that  twenty-four  minutes  after  injecting  3  grains  of  lithium 
salt  under  the  skin  of  a  guinea-pig  the  lithium  is  found  to  be 
present  in  the  crystalline  lens  and  every  part  of  the  body,  it  only 


B   C 


1.  Solar  spectrum  with  Fraunlibfer  lines.  2.  Absorption  spectrum  of  a  concentrated  solution  of  oxyhemo- 
globin ;  all  the  light  is  absorbed  except  in  the  red  and  orange.  3.  Absorption  spectrum  of  a  less  concentrated 
solution  of  oxyhemoglobin.  4.  Absorption  spectrum  of  a  dilute  solution  of  oxyhemoglobin,  showing  the  two 
characteristic'bands.  5.  Absorption  spectrum  of  a  very  dilute  solution  of  oxyhemoglobin,  showing  only  the 
a-band.  6.  Absorption  spectrum  of  a  dilute  solution  of  reduced  hemoglobin,  showing  the  characteristic  single 
band  (to  be  compared  with  spectrum  4).  7.  Absorption  spectrum  of  a  dilute  solution  of  carbon-monoxid- 
hemoglobin  (to  be  compared  with  spectrum  4).  8.  Absorption  spectrum  of.methemoglobin.  9.  Absorption 
spectrum  of  acid  hematin  (alcoholic  solution).  10.  Absorption  spectrum  of  alkaline  hematin  (alcoholic  solu- 
tion) (modified  from  MacMunn,  The  Spectroscope  in  Medicine). 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD. 


283 


being  necessary  to  burn  a  portion  of  the  animal  tissue  in  a 
colorless  flame  in  order  to  see  the  bright-red  line  of  lithium : 
ten  minutes  after  the  injection  it  is  found  in  small  quantities  in 
the  lens,  but  plentifully  elsewhere ;  while  four  minutes  after  the 
injection  lithium  is  not  found  in  the  lens,  but  plentifully  in  the 
aqueous  humor  of  the  eye,  and  in  the  bile.  The  same  rapid 
diffusion  occurs  in  the  human  body.  The  crystalline  lenses  of  per- 
sons who  have  been  operated  upon  for  cataract  have  been  examined, 
these  persons  having  previously  to  the  removal  of  the  lens  been 
given  by  the  stomach  20  grains  of  carbonate  of  lithium  ;  in  three 
and  a  half  hours  it  was  detected  in  each  particle  of  the  lens. 

When  a  sunbeam  passes  through  a  glass  prism,  the  differently 


FIG.  152. — Spectroscope  :  P,  the  glass  prism  ;  A,  the  collimator  tube,  showing  the 
slit  (s)  through  which  the  light  is  admitted ;  B,  the  telescope  for  observing  the 
spectrum. 

colored  rays  which  compose  it  are  separated,  and  if,  after  emerging 
from  the  prism,  the  beam  falls  upon  a  screen,  it  will  appear  as  a 
band  of  different  colors,  beginning  with  red  and  ending  with 
violet;  this  band  is  the  solar  spectrum  (Plate  1,  Fig.  1).  A 
spectroscope  is  an  instrument  for  producing  and  observing  spectra 
(Fig.  152).  The  beam  of  light  which  is  to  be  studied,  from  what- 
ever source  it  may  come,  passes  into  the  collimator  tube  A,  through 
the  slit  s,  and  its  rays,  being  made  parallel  by  a  lens  in  this  tube, 
are  separated  or  dispersed  by  the  prism  p ;  the  spectrum  which 
results  may  then  be  examined  by  an  observer  through  the  telescope 
B.  If  the  source  of  the  light  is  an  incandescent  body,  the  spec- 
trum will  be  a  continuous  one — i.  e.,  there  will  be  nothing  but 
a  band  of  colors,  in  which  the  red  passes  on  to  violet  through 


284 


THE  BLOOD. 


orange,  yellow,  green,  blue,  and  indigo ;  but  if  it  is  the  sun  which 
is  the  source  of  light,  though  this  is  an  incandescent  body,  still  its 
light  passes  through  an  atmosphere  which  absorbs  certain  portions 
of  the  light,  and  the  spectrum  is,  therefore,  crossed  by  dark  lines, 
Fraunhofer  lines.  These  lines  are  fixed,  and  the  more  distinct 
ones  are  designated  by  letters  of  the  alphabet;  thus  in  the  red  are 
A,  B,  and  C ;  in  the  yellow  D,  etc.  As  the  atmosphere  of  the 
sun  absorbs  certain  parts  of  the  light  which  is  transmitted  through 
it,  so  do  many  transparent  substances,  and  the  spectra  of  such 
substances  are  known  as  absorbent  spectra,  in  contradistinction  to 
continuous  spectra,  in  which  no  lines  or  bands  appear.  If,  there- 
fore, the  light  of  the  sun  or  that  from  any  other  source  of  illumi- 


FIG.  153.— The  hematinometer. 


FIG.  154.— The  hematoscope. 


nation  is  passed  through  a  solution  of  one  of  these  substances,  in 
its  spectrum  dark  bands  will  be  seen  at  definite  places  and  in 
definite  numbers,  and  the  identity  of  such  substances  can  thus  be 
determined.  The  positions  occupied  by  these  bands  may  be 
designated  either  by  stating  their  relation  to  the  Fraunhofer  lines, 
or  the  wave-length  of  the  portions  of  the  spectrum  between  which 
absorption  takes  place,  this  being  determined  by  a  scale  which  is 
provided  for  this  purpose. 

For  the  description  of  the  spectra  of  hemoglobin  and  its 
derivatives,  and  the  use  of  the  spectroscope  in  their  differentiation, 
we  are  especially  indebted  to  the  section  on  "  Hemoglobin,"  by 
Gamgee,  in  Schiifer's  Physiology. 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD. 


285 


For  studying  the  visible  spectrum  of  hemoglobin,  Gamgee 
recommends  a  spectroscope  of  the  ordinary  Bunsen  type,  provided 
with  a  single  good  flint-gfass  prism,  or  direct  vision  spectroscopes 
of  the  Browning  or  Hofmann  patterns.  If  minute  quantities  of 
coloring-matter  are  to  be 'investigated,  microspectroscopes  may  be 
used — i.  e.,  direct  vision  spectroscopes  adapted  to  the  eye-piece  of 
a  compound  microscope.  As  the  source  of  light,  he  recommends 
a  gas  lamp,  furnished  with  the  Auer  incandescent  burner. 

It  is  convenient  to  have  the  solutions,  whose  absorption-spectra 
are  to  be  examined,  in  cells  with  perfectly  parallel  sides,  and  a  defi- 
nite width  apart ;  such  an  apparatus  is  the  hematinometer  (Fig.  153). 

The  hematoscope  or  hemoscope  of  Hermann  (Fig.  154)  is  also 
used  for  this  purpose.  In  this  apparatus  the  thickness  of  a  layer 
of  fluid  can  be  regulated  by  sliding  c  toward  F,  and  measured  by 
a  scale  on  c.  F  and  c  are  glass  plates  through  which  and  the 
intervening  fluid  light  is  transmitted  for  spectroscopic  examina- 
tion. 

Spectrum  of   Oxyhemoglobin  (Fig.    155). — Dilute  solutions  of 


70      65 


6O 


55 


50 


4-5 


I 

1 

1 

1 

ll 

1 

BCD                       E    b                 F                                                G 

FIG.  155. — Diagrammatic  representation  of  the  absorption -spectrum  of  oxyhemo- 
globin.  The  numerals  give  the  wave-lengths  in  hundred-thousandths  of  a  milli- 
meter; the  letters  show  the  positions  of  the  more  prominent  Fraunhofer  lines  of  the 
solar  spectrum.  The  red  end  of  the  spectrum  is  to  the  left.  The  a-band  is  to  the 
right  of  D,  the  /3-band  to  the  left  of  K  (after  Eollett). 

oxyhemoglobin  give  two  absorption-bands  between  D  and  E.  The 
band  nearer  D — i.  e.,  the  red  end  of  the  spectrum — is  known  as  the 
"  a-band  ";  the  one  near  E  is  the  "  /3-band,"  and  is  broader,  lighter, 
and  less  clearly  defined  than  the  a-band.  The  center  of  the 
a-band  corresponds  to  a  wave-length  of  579  millionths  of  a  milli- 
meter (/I  579)  ;  while  the  center  of  the  /3-band  corresponds  to 
A  553.8. 

Spectrum  of  Hemoglobin  (Reduced  Hemoglobin)  (Fig.  156).— 
Oxyhemoglobin  may  be  reduced  to  hemoglobin  by  adding  to  its 
solutions  Stokes'  reagent,  which  is  made  by  dissolving  2  parts  by 
weight  of  ferrous  sulphate,  adding  3  parts  of  tartaric  acid,  and 
then  adding  ammonia  until  the  reaction  is  distinctly  alkaline. 
When  thus  reduced  the  a-  and  /9-bands  disappear,  and  the  "  /-band  ' 
appears  ;  this  is  a  single  band  between  D  and  E,  its  darkest  part 
being  nearer  D  than  E,  and  corresponding  to  about  I  550.  If  the 
solution  is  shaken  with  air,  the  appearance  of  the  «-  and  /9-bands 
shows  that  oxyhemoglobin  has  been  formed. 


286 


THE  BLOOD. 


Carbon-monoxid  Hemoglobin. — This  derivative  of  hemoglobin 
presents  two  bands  resembling  those  of  oxyhemoglobin,  except 
that  they  are  nearer  the  violet  end  of  the  spectrum. 

Methemoglobin  and  hematin  have  each  a  characteristic  spec- 
trum. 

Development  of  Red  Corpuscles. — This  is  described  by  Schafer 
as  taking  place  in  the  following  manner :  In  the  developing 
embryo  some  cells  of  the  mesoblast  become  united,  forming  a 
protoplasmic  network.  These  cells  are  nucleated,  and  their  nuclei 
multiply,  colored  protoplasm  forming  an  aggregation  around 
them.  The  protoplasm  of  this  network  is  hollowed  out  by  an 
accumulation  of  fluid ;  in  this  manner  the  capillary  blood-vessels 
are  formed.  The  nuclei  with  their  colored  protoplasm  are  set  free, 
becoming  embryonic  blood-corpuscles.  The  blood-corpuscles  are 
at  this  period,  therefore,  nucleated  cells.  The  corpuscles  at  this 
time  have  a  diameter  of  from  10  /jt  to  16  /JL,  and  are  spherical. 
They  possess  the  power  of  ameboid  movement,  and  thus  resemble 


70     65 


60 


55 


E     b 


FIG.  156. — Diagrammatic  representation  of  the  absorption-spectrum  of  hemo- 
globin (reduced  hemoglobin).  The  numerals  give  the  wave-lengths  in  hundred- 
thousandths  of  a  millimeter;  the  letters  show  the  positions  of  the  more  prominent 
Fraunhofer  lines  of  the  solar  spectrum.  The  red  end  of  the  spectrum  is  to  the  left. 
The  single  diffuse  absorption-band  lies  between  D  and  E  (after  Rollett). 

the  white  corpuscles.  It  has  been  suggested  that  these  should  be 
called  blood-cells  rather  than  blood-corpuscles. 

The  liver  begins  to  be  formed  about  the  third  week  of  em- 
bryonic life,  and  about  the  third  month  occupies  most  of  the 
abdominal  cavity.  This  organ,  together  with  the  spleen,  thymus, 
and  lymphatic  glands,  also  produces  blood-cells  which  are  nucle- 
ated, are  at  first  colorless,  and  afterward  acquire  the  characteristic 
color. 

At  a  later  period  of  embryonic  life,  about  the  second  month, 
non-nucleated  disk-shaped  corpuscles  make  their  appearance. 
These  originate  to  some  extent  in  connective-tissue  cells,  a  portion 
of  the  cell  becoming  colored,  and  separate  into  globular  particles, 
which  subsequently  become  the  discoid  corpuscles.  The  connec- 
tive-tissue cells  afterward  become  hollowed  out,  and,  joining  with 
other  cells  which  have  gone  through  the  same  process,  blood- 
vessels are  formed.  This  later  embryonic  formation  of  blood- 
corpuscles  does  not  involve 'the  cell-nuclei,  as  does  that  of  the 
earlier  period.  The  nucleated  cells  are  replaced  by  the  non- 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  287 

nucleated  about  the  end  of  the  fourth  month,  but  it  is  still  a  moot 
question  whether  any  of  the  nucleated  cells  are  actually  concerned 
in  the  formation  of  the  non-nucleated. 

Non-nucleated  blood-corpuscles  are  also  formed  in  the  medulla 
or  marrow  of  bones,  and  in  the  spleen.  In  the  red  marrow  of 
bones  are  found  nucleated  cells  possessing  the  power  of  ameboid 
movement,  the  true  "marrow-cells"  of  Kolliker.  In  the  proto- 
plasm of  these  cells  hemoglobin  is  formed,  and  this  portion  of  the 
protoplasm  becomes  converted  into  the  non-nucleated  corpuscle. 
There  are,  besides  these  marrow-cells,  others  of  smaller  size, 
erythroblasts,  likewise  ameboid,  nucleated,  and  colorless,  which 
later  undergo  karyokinesis  ;  the  daughter-cells  become  colored,  lose 
their  nuclei,  and  are  converted  into  the  mature  non-nucleated  red 
blood-corpuscles.  It  is  to  the  red  marrow  that  is  to  be  principally 
attributed  the  formation  of  the  red  corpuscles  in  adult  life.  This 
process  is  called  hematopoiesis,  and  is  a  constant  process,  new 
corpuscles  taking  the  place  of  the  old  which  have  outlived  their 
usefulness.  It  occurs  to  a  much  greater  extent  than  usual  after 
hemorrhages. 

In  the  spleen  are  to  be  found  cells  somewhat  resembling  the 
erythroblasts  just  described,  and  it  is  the  opinion  of  some  authori- 
ties that  these  are  also  sources  of  the  red  blood-corpuscles. 

Destruction  of  Red  Corpuscles. — The  duration  of  a  red  blood- 
corpuscle  is  undetermined,  but  it  is  doubtless  limited.  Some 
authorities  place  its  life  at  from  three  to  four  weeks.  Old  corpus- 
cles constantly  undergo  disintegration  and  new  ones  appear.  The 
fact  that  fewer  corpuscles  are  found  in  the  blood  of  the  hepatic  than 
in  that  of  the  portal  vein,  and  the  additional  fact  that  biliary 
pigment  is  formed  from  the  coloring-matter  of  the  blood,  indicate 
that  in  the  liver  a  part,  at  least,  of  these  destructive  changes  takes 
place. 

The  spleen  is  also  regarded  by  some  authorities  as  being  an 
organ  in  which  red  corpuscles  are  destroyed.  The  argument 
advanced  in  favor  of  this  theory  is  that  some  of  the  susten- 
tacular  or  supporting  cells  of  the  splenic  pulp  contain  colored 
granules  which  resemble  the  hematin  of  the  blood ;  in  others  red 
corpuscles  are  found  in  various  stages  of  disintegration.  The 
explanation  is  that  these  large  cells  are  engaged  in  the  process  of 
destroying  used-up  corpuscles.  Opposed  to  this  theory  is  the  fact 
that  the  blood  coming  from  the  spleen  contains  no  hemoglobin  in 
solution,  which  it  certainly  would  do  if  red  corpuscles  were 
destroyed  in  that  organ ;  besides,  after  removal  of  the  spleen  the 
destruction  of  corpuscles  apparently  goes  on  much  the  same  as 
before. 

There  seems  to  have  been  an  idea  in  the  minds  of  some  that 
it  wras  essential  that  some  organ  or  organs  should  be  charged  with 
the  duty  of  destroying  the  red  corpuscles.  This  does  not,  how- 


288  THE  BLOOD. 

ever,  follow.  There  is  no  reason  why  many  of  the  corpuscles 
may  not  undergo,  disintegration  in  any  part  of  the  circulatory 
system,  wherever  they  happen  to  be  at  the  time  the  change  takes 
place.  The  large  extent  of  blood-vessels  in  the  liver  would 
account  for  the  destruction  that  takes  place  there,  without  regard 
to  any  special  function  of  this  organ  connected  with  such  destruc- 
tion. If,  as  there  is  reason  to  believe,  the  pigment  of  the  bile  and 
the  urine  are  formed  from  that  of  the  blood,  the  number  of  corpus- 
cles daily  destroyed  must  be  very  great. 

Function  of  Red  Corpuscles. — The  red  corpuscles  are  the 
carriers  of  oxygen  from  the  lungs,  where  it  is  received,  to  the 
tissues,  which  appropriate  it.  This  function  is  due  to  the  hemo- 
globin, which  has  a  great  affinity  for  oxygen. 

Diapedesis. — In  inflammatory  conditions  the  red  corpuscles 
pass  through  the  walls  of  the  capillaries,  constituting  diapedesis 
(p.  290).  This  is  not  an  active  process,  as  in  the  case  of  the 
leukocytes,  but  a  passive  one ;  for  while  the  latter  can  make 
their  way  through  uninjured  walls,  it  is  only  after  these  have  thus 
migrated  that  through  the  same  opening  the  red  corpuscles  can 
pass. 

Colorless  Blood-corpuscles. — These  are  also  called  white  cor- 
puscles and  leukocytes.  They  consist  of  granular  protoplasm,  and 
contain  one  nucleus  or  more.  When  in  a  condition  of  rest  they 
are  spheroidal  in  shape,  with  a  diameter  of  about  10  /^,  and  possess 
the  power  of  ameboid  movement ;  their  shape  is  constantly 
changing. 

The  number  of  leukocytes  in  the  blood  is  commonly  said  to  be, 
compared  with  the  red  corpuscles,  as  1  to  350  or  1  to  750,  or,  as 
others  state  it,  about  10,000  in  a  cubic  millimeter  of  blood  ; 
but  these  figures  are  of  very  little  value,  so  greatly  do  the  propor- 
tions vary  under  different  conditions.  Thus  Hirst  found  before 
breakfast,  1  to  1800;  one  hour  after,  1  to  700;  before  dinner,  1 
to  1500;  after  dinner  (1  o'clock),  1  to  400  ;  two  hours  later,  1  to 
1475;  after  supper  (8  o'clock),  1  to  550;  12  p.  M.,  1  to  1200. 
After  eating  the  number  is  much  increased.  This  increase  also 
occurs  after  the  loss  of  blood,  during  suppurative  processes,  and 
after  the  use  of  bitter  tonics  ;  while  in  a  state  of  hunger  or  defi- 
cient nourishment  the  number  is  diminished.  The  proportion  also 
varies  in  different  parts  of  the  circulatory  system  ;  thus  in  the 
splenic  vein  it  has  been  found  to  be  as  1  to  60  ;  in  the  splenic 
artery,  1  to  2260 ;  hepatic  vein,  1  to  170 ;  and  portal  vein,  1 
to  740. 

Leukocytosis  is  defined  as  a  temporary  increase  in  the  number 
of  leukocytes  in  the  blood.  It  occurs  normally  during  digestion 
and  in  pregnancy,  and  is  seen  as  a  pathologic  condition  in  inflam- 
mation, traumatic  anemia,  various  fevers,  etc.  Leukocythemia  or 
leukemia,  on  the  other  hand,  is  a  fatal  disease  with  marked 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  289 

increase  in  the  number  of  leukocytes  in  the  blood,  together  with 
enlargement  and  proliferation  of  the  lymphoid  tissue  of  the 
spleen,  lymphatic  glands,  and  bone-marrow.  The  disease  is 
distinguished  as  lymphatic,  splenic,  lymphaticosplenic,  medullary  or 
myelogenic,  and  lienomyelogenous,  according  as  the  disease  involves 
the  lymphatics,  the  spleen,  both  the  spleen  and  the  lymphatics, 
the  bone-marrow,  or  both  the  spleen  and  bone-marrow.  It  may 
be  due  to  disorder  of  the  intestines  (intestinal  leukemia},  of  the 
liver  (hepatic  leukemia),  or  to  disease  of  the  tonsils  (amygdaline 
leukemia) — Dorland's  Medical  Dictionary. 

If  peptones  or  leech  extract  are  injected  into  the  blood-vessels, 
there  is  at  first  a  diminution  in  the  number  of  the  leukocytes, 
especially  the  poly  nuclear  variety  ;  this  is  termed  the  leukocyto- 
penic  phase ;  afterward  the  number  is  increased,  constituting  the 
leukocytotic  phase. 

Acute  local  inflammation  causes  similar  changes  as  do  these 
injections,  but  the  diminution  in  the  number  of  leukocytes  in  this 
case  largely  affects  the  coarsely  granular  variety,  while  the  after- 
increase  is  found  mainly  in  the  finely  granular  corpuscles  (Schafer). 
It  has  been  observed  that  the  blood  clots  more  readily  when  the 
coarsely  granular  cells  are  relatively  few  in  number,  and  Schafer 
thinks  this  may  explain  the  more  ready  clotting  of  blood  in  in- 
flammatory conditions. 

Varieties  of  Colorless  Corpuscles. — Ehrlich  classifies  the  color- 
less cells  according  to  the  kind  of  anilin  stain  which  the  majority 
of  the  contained  granules  take ;  thus  cells  whose  granules  are 
stained  by  basic  dyes,  as  methylene-blue,  he  terms  basophil ; 
while  those  whose  granules  are  stained  by  acid  dyes,  such  as  eosin, 
he  calls  oxyphil  or  eosinophil.  These  terms  are  also  written 
basophile,  oxyphile,  and  eosinophile. 

Still  another  classification  divides  the  colorless  corpuscles  into 

(1)  lymphocytes,  which  are  characterized  by  being  small,  having  a 
round  vesicular  nucleus,  and  named  from  their  resemblance  to  the 
leukocytes  of  lymph-glands,  but  not  possessing  ameboid  movement; 

(2)  mononuclear  leukocytes,  cells   with   a   single   nucleus ;  and  (3) 
polymorphous  or  polynucleated  leukocytes,  characterized  by  having 
more   than   one   nucleus  or  else  a  divided  nucleus,  the  divisions 
being  connected   by  protoplasm.     Nos.  2  and   3  possess  ameboid 
movement.     It  is  believed  by  some  authorities  (Howell)  that  these 
varieties  are  simply  different  stages  in  the  development  of  a  single 
type  of  cell,  the  lymphocytes  being  the  youngest  and  the  polynu- 
cleated leukocytes  the  oldest.     The  granules  of  the   mononuclear 
variety  are  coarser  and  stain  more  deeply  with  eosin  than  do  those 
of  the  polynuclear,  but  constitute   only  about  5  per  cent,  of  the 
total  colorless  corpuscles  ;  while   the  basophil  cells  are  not  often 
found.     Still   another  variety,  called   hyalin,  is  described  ;  these 
have  no  granules.     It  should  be  borne  in  mind  that  it  is  the  kind 

19 


290 


THE  BLOOD. 


of  dye  which  the  protoplasm  takes  which  determines  the  variety 
of  the  corpuscles ;  the  nuclei  of  all  the  leukocytes  is  basophil. 

Composition   of    Leukocytes. — The    chemical    composition   of 
leukocytes  is  given  (Lilienfeld)  as  follows : 

Water .    .   I    . 88.51 

Solids 11-49 


The  solids  are  : 

Proteid 1.76 

Nuclein 68.78 

Histon  (i.  e.,  proteid  part  of  the 
nucleoproteid )      8.67 


100.00 


Lecithin 7  51 

Fat 4.02 

Cholesterin 4.40 

Glycogen  . 0.80 


This  analysis  of  the  cells  is  of  those  from  the  thymus,  but  we 
are  justified  in  concluding  that  the  colorless  corpuscles  of  the 
blood  which  originate  from  lymphoid  structures  have  a  similar 
composition.  It  is,  however,  impossible  to  investigate  the  color- 
less blood-corpuscles  by  macrochemical  methods.  Micro-chem- 
ically  they  can  be  shown  to  contain  fat  and  glycogen  (Halli- 
burton). 

Functions  of  the  Colorless  Corpuscles. — The  movements  which 
occur  in  protoplasm,  known  as  ameboid  movements,  have  been 
already  described  (p.  24).  This  power  is  possessed  by  the  leuko- 
cytes, by  virtue  of  which  they  pass  through  the  walls  of  the  capil- 
lary blood-vessels,  this  power  being  diapedesis  or  migration. 
There  is  no  doubt  that  this  occurs  normally  to  a  certain  extent, 
but  to  a  much  greater  extent  under  abnormal  conditions,  as  in  in- 
flammations. When  these  migrated  leukocytes  accumulate  out- 
side the  blood-vessels,  and  have  lost  their  vitality,  they  consti- 
tute pus. 

Phagocytosis. — Metschnikoff  has  advanced  the  theory  that 
one  of  the  important  functions  of  the  leukocytes  is  to  ingest  and 
digest  bacteria  ;  this  constitutes  phagocytosis.  In  this  process  the 
polynucleated  cells  are  the  most  active.  There  is  no  doubt  that 
by  virtue  of  their  ameboid  movement  the  leukocytes  do  surround 
and  take  into  their  protoplasm  foreign  matter,  and  if  bacteria  are 
present  they  are  likewise  ingested,  but  whether  they  are  thus 
taken  in  while  in  a  living  state  and  destroyed,  or  only  after  their 
vitality  has  left  them,  is  a  question.  Those  who  favor  the  theory 
look  upon  the  leukocytes  as  the  protectors  of  the  human  race 
against  the  incursions  of  infectious  diseases,  if  their  vitality  is 
sufficient  to  overcome  and  destroy  the  bacteria  of  these  diseases ; 
whereas  if  the  bacteria  are  the  more  powerful,  then  the  disease 
obtains  a  foothold.  A  person  is  said  to  be  immune  when  on  ex- 
posure to  a  communicable  disease,  such  as  scarlet  fever,  measles, 
etc.,  he  does  not  contract  it,  and  the  explanations  which  have  been 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  291 

given  to  account  for  this  immunity  are  many  and  various.  One 
of  these  is  the  "  phagocytosis  theory  of  Metschnikoff  "  :  That 
"  immunity  against  infection  is  essentially  a  matter  between  the 
invading  bacteria  on  the  one  hand  and  the  leukocytes  of  the  tissues 
on  the  other ;  that  during  the  first  attack  of  the  disease  the  white 
blood-corpuscles  gain  a  tolerance  to  the  poisons  of  the  bacteria, 
and  so  are  able  to  resist  the  next  incursion  of  the  enemy."  At  the 
present  time,  however,  the  theory  of  immunity  which  is  most  gen- 
erally accepted  is  that  known  as  "  the  lateral-chain  theory  "  of 
Ehrlich,  for  the  explanation  of  which  the  reader  is  referred  to  text- 
books on  Pathology.  The  phagocytotic  power  of  the  leukocytes  is 
also  manifested  in  their  destruction  of  the  products  of  inflammation. 

It  is  believed  that  the  colorless  corpuscles  are  concerned  in  the 
process  of  coagulation  of  the  blood  (p.  294). 

For  the  consideration  of  other  properties  of  the  leukocytes,  the 
reader  is  referred  to  pages  24,  25,  293,  and  300. 

Development  of  Colorless  Corpuscles. — The  first  leukocytes  are 
formed  from  the  embryonic  cells  of  the  mesoblast,  and  afterward 
from  lymphatic  glands  and  lymphatic  tissues  generally.  They 
pass  into  the  lymphatics  and  thence  into  the  blood-vessels. 

Plaques. — These  are  also  known  as  blood-plates,  blood-platelet^^ 
and  hematoblasts.  They  are  circular  or  elliptical  in  shape,  and 
smaller  than  the  red  corpuscles,  but  vary  very  much  in  size,  from 
0.5  p.  to  5.5  fly  and  are  colorless.  Their  number  is  said  to  vary 
from  180,000  to  more  than  600,000. 

Various  theories  have  been  propounded  to  explain  their  occur- 
rence in  blood.  One  of  these  is  that  they  are  not  formed  struct- 
ures, but  simply  precipitates  of  nucleoproteid  from  the  plasma. 
This  theory  is,  we  think,  no  longer  held.  There  is  little  doubt 
that  they  are  formed  elements  existing  normally  in  the  blood, 
although  the  theory  of  Hayem,  who  discovered  them,  that  red 
corpuscles  are  formed  from  them,  is  no  longer  maintained. 

Lilienfeld  has  obtained  from  them  a  nucleo-albumin,  called  by 
him  nucleohiston,  which  is  also  found  in  the  nuclei  of  the  leuko- 
cytes, and  it  is  believed  by  many  that  the  blood-plates  are  nothing 
more  than  the  nuclei  of  the  polynucleated  colorless  corpuscles, 
which  are  set  free  when  these  corpuscles  disintegrate,  and  that 
these  plates  also  disintegrate,  and  are  dissolved  in  the  plasma. 
Their  possible  relation  to  the  coagulation  of  the  blood  is  discussed 
in  connection  with  that  subject  (p.  294). 

Blood-plasma. — The  plasma  or  liquor  sanguinis  is  yellowish  in 
color  and  alkaline  in  reaction,  having  a  specific  gravity  of  1027 
to  1031.  It  contains  the  following  ingredients  :  Water,  inorganic 
salts,  extractives,  enzymes,  proteids,  and  gases. 

Water  and  Inorganic  Salts. — Water  exists  in  plasma  to  the 
approximate  amount  of  90  per  cent.,  so  that  10  per  cent,  consists 
of  solids.  Of  these  solids,  about  0.85  per  cent,  are  inorganic 


292  THE  BLOOD 

salts ;  and  of  these,  sodium  chlorid  is  the  most  abundant,  being 
present  to  the  amount  of  0.55  per  cent.  Sodium  carbonate  is 
present  to  the  amount  of  0.15  per  cent. ;  and  this  salt  is  the 
principal  cause  of  the  alkalinity  of  the  plasma,  and  gives  it  its 
power  to  absorb  carbon  dioxid.  The  salts  of  the  plasma  have  not 
been  exactly  determined,  but,  according  to  Schmidt,  the  following 
table  gives  those  that  probably  occur,  with  their  percentages : 

Potassium  sulphate 0.0281 

Potassium  chlorid 0.0359 

Sodium  chlorid 0.5546 

Sodium  phosphate 0.0271 

Sodium  carbonate 0.1532 

Calcium  phosphate       0  0298 

Magnesium  phosphate 0.0218 

Calcium  chlorid  is  probably  also  present,  and  traces  of  a 
fluorid  have  likewise  been  found. 

Extractives. — These  include  carbohydrates,  of  which  there  are 
three :  Glyc6gen,  probably  derived  from  the  leukocytes ;  an 
animal  gum;  and  dextrose.  This  last,  we  have  seen,  is  always 
present  in  human  blood  to  the  amount  of  about  0.12  per  cent., 
being  much  more  abundant  in  portal  blood  during  the  digestion 
of  carbohydrates.  Fat  is  also  a  constituent  of  the  plasma,  the 
amount  being  increased  by  its  absorption  after  a  meal  containing 
it.  Lecithin,  cholesterin,  lipochrome  (which  gives  the  plasma  its 
yellow  color),  urea,  uric  acid,  kreatin,  kreatinin,  and  occasionally 
hippuric  acid  are  also  present. 

Enzymes. — Plasma  contains  at  least  five  enzymes  :  (1)  An  amyl- 
olytic,  which  is,  according  to  some  authorities,  produced  by  the  red 
cells,  while  others  attribute  it  to  the  leukocytes ;  (2)  a  glycolytic, 
causing  a  destruction  of  some  of  the  dextrose  in  the  blood.  Al- 
though the  existence  of  this  enzyme  is  denied,  there  is  strong  evi- 
dence in  favor  of  its  existence.  According  to  Spitzer,  it  exists  in 
both  red  and  white  blood-cells  and,  indeed,  in  all  tissue-cells.  It 
acts  only  in  the  presence  of  oxygen  ;  (3)  a  lipolytic,  called  lipase; 
(4)  a  coagulating  thrombin  or  prothrombin,  which  causes  coagula- 
tion of  the  blood  under  some  circumstances  (p.  293)  ;  (5)  a  proteolytic. 
The  destruction  of  the  exudate  of  pneumonia  is  attributed  to  this 
enzyme. 

Proteids. — These  are  :  (1)  Serum-albumins,  a,  ft,  and  y  (p.  108)  ; 
(2)  serum-globulin  or  paraglobulin  (p.  110);  (3)  fibrinogen  (p. 
110);  (4)  nucleoproteid. 

The  total  proteids  in  human  plasma  are  7.62  per  cent.,  of 
which  3.10  per  cent,  are  globulins,  and  4.52  per  cent,  albumins. 

The  proteids  of  the  plasma  have  been  already  discussed  in 
dealing  with  this  class  of  physiologic  ingredients  (p.  126),  but 
one  of  them,  fibrinogen,  deserves  special  notice  at  this  time  because 
of  its  relation  to  the  process  of  blood-coagulation. 


MICROSCOPIC  STRUCTURE  OF  THE  BLOOD.  293 

Fibrinogen. — Although  it  is  customary  to  speak  of  fibrinogen 
as  if  it  was  a  simple  substance,  yet  the  fact  that  when  it  is  dis- 
solved in  salt  solution  and  heated  to  a  temperature  between  52° 
C.  and  55°  C.  only  a  part  of  the  proteid  is  coagulated,  and  that 
when  the  temperature  reaches  65°  C.  another  portion  is  thrown 
down,  has  led  Hammarsten  to  regard  it  as  made  up  of  fibrinogen 
proper,  which  coagulates  at  the  lower  temperature,  and  a  globulin, 
fibrin-globulin,  which  is  coagulated  at  the  higher  temperature. 
It  is  believed  that  a  nucleoproteid  is  also  combined  with  these  two 
proteids  to  make  up  what  is  commonly  termed  fibrinogen. 

Origin  of  Fibrinogen. — Matthews,  after  a  very  elaborate  study 
of  the  subject,  reported  in  the  American  Journal  of  Physiology, 
concludes  that  the  decomposing  leukocytes  of  the  blood,  and 
chiefly  those  of  the  intestinal  area,  are  the  sources  of  the  blood 
fibrinogen,  and  supports  this  opinion  :  u(l)  By  the  increase  in  the 
per  cent,  of  fibrinogen  in  all  cases  of  prolonged  leukocytosis 
accompanying  suppuration ;  (2)  by  the  increase  in  fibrinogen 
during  leukocythemia ;  (3)  by  the  increase  in  fibrinogen  in  pneu- 
monia, erysipelas,  acute  rheumatism,  peritonitis,  and  similar  in- 
flammatory conditions;  (4)  by  the  fact  that  fibriuogen  is  not 
simply  transformed  proteid  of  the  food,  as  indicated  by  its  con- 
tinued formation  during  fasting,  and  its  failure  to  increase  during 
proteid  digestion ;  (5)  by  the  observation  that  neither  the  spleen, 
muscles,  kidneys,  pancreas,  nor  brain  appears  to  be  essential  to  its 
formation  ;  (6)  by  the  well-known  fact  that  there  is  present  in 
the  cell-body  of  the  leukocyte  a  substance  which,  by  the  action 
of  a  substance  coming  from  the  nucleus  or  arising  in  its  neighbor- 
hood, is  thrown  into  a  fibrillar  form  closely  resembling  fibrin- 
fibrils,  and  like  them  contractile ;  (7)  by  the  fact  that  the  leuko- 
cytes are  constantly  going  to  pieces  in  the  body,  hence  must  be 
adding  constantly  to  the  proteid  constituents  of  the  blood  ;  (8)  by 
the  close  correspondence  existing  between  the  fibrinogen-content 
of  the  blood  and  the  excretion  of  uric  acid  ;  and  (9)  by  the  fact 
that  the  intestine,  which  is  rich  in  leukocytes,  appears  to  be  the 
chief  source  of  the  fibrinogen  of  the  body." 

In  this  article  Matthews  makes  the  following  statement,  which 
is,  to  say  the  least,  suggestive,  although,  of  course,  as  yet  not 
demonstrated  :  "  If  fibrinogen  is  derived  from  the  leukocytes,  as  the 
preceding  considerations  indicate,  and  if  Schmidt's  and  Morner's 
observations  on  paraglobulin  indicating  its  origin  in  the  leukocyte 
prove  well  founded,  the  conclusion  would  seem  obvious  that  the 
proteids  of  the  blood  are  derived  from  the  leukocytes.  This 
would  strongly  confirm  Hoifrneister's  view  that  the  leukocytes  are 
pre-eminently  active  in  proteid  absorption  and  assimilation.  It 
would  lead  to  the  interesting  conclusion  that  the  organism  lives  on 
its  leukocytes  much  as  the  egg-cells  of  some  forms  live  on  their 
follicle-cells.  If  this  were  so,  it  would  explain  (1)  the  true 


294  THE  BLOOD. 

function  of  the  leukocytes  and  the  elaborate  arrangements  for 
their  production  in  the  body ;  (2)  their  congregation  and  great 
reproduction  in  the  intestinal  area  during  a  proteid  meal ;  (3)  the 
positive  chemotaxis  they  exhibit  toward  the  proteids,  albumoses, 
and  other  products  of  digestion  ;  (4)  the  maintenance  of  the  pro- 
teid constituents  of  the  blood  during  fasting ;  (5)  the  fate  of  the 
bodies  of  the  leukocytes  w.hen  they  disintegrate  ;  (6)  the  fact  that 
no  products  of  digested  proteids  are  found  in  the  blood  during 
proteid  digestion.  It  would  make  the  leukocyte,  in  fact,  a  store- 
house of  the  surplus  proteid  food  of  the  body,  just  as  the  liver- 
cell  is  a  storehouse  of  surplus  carbohydrate  food.'7 

Nucleoproteid. — In  regard  to  this  constituent  of  plasma,  Schafer 
says  that  it  is  doubtful  if  it  exists  in  the  plasma  of  circulating 
blood,  and  that  beyond^  the  fact  of  its  appearing  to  be  one  of  the 
essential  factors  in  the  formation  of  fibrin,  very  little  is  known 
about  it.  It  is  regarded  as  being  derived  from  the  leukocytes  and 
plaques  at  the  time  the  blood  is  withdrawn  from  the  vessels.  A 
small  amount  comes  from  the  red  corpuscles.  The  reasons  for 
this  belief  as  given  by  Schiifer  are : 

1.  White  blood-corpuscles  and  similar  cells  (lymph-cells,  thy- 
mus-cells,  etc.)  always  contain  a  considerable  amount  of  nucleo- 
proteid. 

2.  In  plasma  obtained  by  subsidence  of  the  corpuscles  there  is 
most  nucleoproteid  in  the  lower  layers,  which  contain  most  leuko- 
cytes ;  and  least  in  the  upper,  which  contain  very  few. 

3.  Fluids  which  collect   in    the   serous  cavities   of  the  body 
(pericardial  fluid,  hydrocele  fluid,  ascitic  fluid)  frequently  contain 
no  leukocytes.     When   this  is  the  case  they  are  also  devoid  of 
nucleoproteid  and  of  the  property  of  spontaneous  coagulability, 
although  they  contain  fibriuogen.    Solutions  of  this  nucleoproteid 
are  coagulated  at  65°  C.,  and  at  60°C.,  if  free  alkali  is  present,  it 
is  split  into  nucleiu  and  a  proteid.     If  soluble  salts  of  lime  are 
present,  the  nucleoproteid  unites  with  the  lime,  and  the  product 
has   the    property    of  converting   fibrinogen    into   fibrin,    and    is 
identical  with  fibrin-ferment  or  thrombi  n  ;   inasmuch  as  the  nucleo- 
proteid precedes  and  becomes  changed  into  thrombin,  it  is  termed 
prothrombin. 

Gases. — The  plasma  contains  oxygen  and  nitrogen  in  solution, 
and  carbon  anhydrid  both  in  solution  and  also  in  combination  as 
sodium  carbonate  and  bicarbonate.  The  amount  of  oxygen  in 
the  plasma  is  very  small  :  in  the  dog,  0.25  per  cent. 

Coagulation  of  Blood. — When  blood  is  withdrawn  from 
the  circulation  it  undergoes  coagulation,  consisting  in  the  produc- 
tion of  a  clot  from  which  is  subsequently  expressed  a  fluid — the 
serum.  The  length  of  time  required  for  coagulation  varies  in  the 
blood  of  different  animals.  In  human  blood  the  change  manifests 
itself  in  about  two  or  three  minutes.  When  the  blood  is  withdrawn 


COAGULATION  OF  BLOOD.  295 

from  the  vessel  it  is  fluid,  but  at  the  end  of  two  or  three  minutes  its 
fluidity  is  so  much  diminished  that  it  will  not  flow  ;  this  consis- 
tency increases  until  at  the  end  of  eight  or  ten  minutes  the  entire 
quantity  of  blood  becomes  a  mass  resembling  currant-jelly  in  color 
and  consistency.  This  jelly-like  mass  becomes  more  and  more 
consistent,  squeezing  out  upon  its  surface  a  few  drops  of  a  straw- 
colored  fluid — the  serum.  As  the  shrinking  of  this  gelatinous 
mass — the  dot — continues,  it  separates  from  the  sides  of  the  vessel 
in  which  the  blood  was  received,  and  the  serum  is  squeezed  out  on 
all  sides,  until  at  length  there  is  a  more  or  less  solid  clot  floating 
in  a  considerable  quantity  of  serum.  The  entire  process  requires 
from  ten  to  forty-eight  hours.  When  examined,  the  clot  is  found 
to  be  made  up  of  fibrin  and  corpuscles,  the  red  corpuscles  giving 
to  it  the  red  color.  The  white  corpuscles  may  at  first  be  entangled 
in  the  meshes  of  the  fibrin,  but  by  virtue  of  their  ameboid  move- 
ment they  soon  escape  into  the  serum.  The  serum  has  the  same 
composition  as  the  plasma  minus  the  fibrinogen. 

Although  the  corpuscles  are  denser  than  the  plasma,  still  the 
difference  is  so  slight  and  the  process  of  coagulation  so  rapid  that 
before  they  can  settle  they  are  entangled  in  the  meshes  of  the 
fibrin  as  it  forms,  and  thus  become  a  part  of  the  clot.  If  any- 
thing occurs  to  delay  coagulation,  the  corpuscles  settle,  and  the  clot 
is  then  less  red  and  more  yellowish.  This  delay  may  be  brought 
about  by  the  addition  of  a  27  per  cent,  solution  of  magnesium 
sulphate  or  other  neutral  salt,  the  plasma  being  then  termed 
salted  plasma  ;  it  occurs  also  in  inflammatory  processes,  and  hence 
in  the  olden  time,  when  venesection  or  '"bleeding"  was  commonly 
practised,  this  crusta  phlogistica,  or  "  bufly  coat,"  was  always  looked 
for  by  the  physician,  and  when  it  formed  was  considered  as  evidence 
that  the  bleeding  was  justifiable.  That  the  physicians  of  that  period 
were  not  always  right  in  this  judgment  is  now  known,  for  a  bufly 
coat  will  form  in  blood  which  is  hydremic,  a  condition  in  which 
bleeding  is  contraindicated.  In  horses'  blood,  which  normally 
coagulates  very  slowly,  this  "  bufly  coat "  always  forms.  It  is 
simply  the  fibrin  without  the  corpuscles,  or  at  least  without  enough 
of  them  to  give  the  red  color  which  the  clot  usually  possesses. 

Influences  which  Retard  Coagulation. — Coagulation  is  retarded 
by  cold,  by  solutions  of  sodium  or  magnesium  sulphate,  by  a 
diminished  amount  of  oxygen,  by  an  increased  amount  of  carbon 
dioxid,  by  acids  or  alkalies,  by  egg-albumin,  by  oil,  by  a  solution 
of  albumose,  and  by  extract  of  the  head  of  the  leech.  It  is  well 
known  that  the  blood  drawn  from  the  vessels  by  this  animal  does 
not  coagulate  within  its  body.  It  is  supposed  that  its  saliva  contains 
an  albumose  which  prevents  clotting  of  the  blood.  Solutions 
of  potassium  or  sodium  oxalate  also  prevent  coagulation.  The 
explanation  of  this  action  is  that  the  calcium  which  is  required  for 
the  process  is  precipitated  as  calcium  oxalate.  Venous  blood 


296  THE  BLOOD. 

coagulates  more  slowly  than  arterial,  because  of  the  lessened 
amount  of  oxygen  and  the  increased  amount  of  carbon  dioxid. 
It  is  said  that  blood  from  the  capillaries  does  not  coagulate  at  all. 

It  is  the  prevalent  opinion  that  menstrual  blood  does  not  clot ; 
this,  strictly  speaking,  is  not  true.  If  the  blood  was  collected  as 
it  comes  from  the  uterine  vessels,  it  would  doubtless  coagulate  as 
does  other  blood ;  but  when  it  is  mixed  with  the  acid  vaginal 
mucus  its  coagulation  is  then  impeded.  Then,  too,  during  the 
menstrual  period  some  of  the  blood  undergoes  clotting  within  the 
uterine  cavity  or  in  the  vagina :  that  which  escapes  and  which  is 
regarded  as  menstrual  blood  is  for  the  most  part  only  serum, 
which,  of  course,  does  not  coagulate. 

Influences  which  Hasten  Coagulation. — Heat  hastens  coagulation, 
as  does  agitation  of  the  blood,  as  in  whipping  it  with  twigs  or  rods. 
In  general,  anything  which  tends  to  break  down  the  leukocytes  or 
plaques  from  which  the  nucleoproteid  prothrombin  is  derived  will 
cause  the  latter  to  be  set  free  and  favor  coagulation. 

Causes  of  Coagulation. — Perhaps  no  physiologic  question  has 
excited  more  controversy  than  that  which  deals  with  the  cause  of 
blood-coagulation.  Normally,  blood  remains  fluid  within  the 
blood-vessels,  but  within  a  few  minutes  after  withdrawal  it  begins 
to  undergo  coagulation.  What  is  the  explanation  ? 

It  has  been  suggested  that  blood-coagulation  is  due  to  exposure 
to  the  air.  It  is  true  that  contact  with  the  air  hastens  coagula- 
tion, but  that  this  is  unnecessary  to  the  process  is  shown  by  the 
fact  that  coagulation  will  take  place  under  mercury  when  all  air  is 
excluded.  Nor  can  it  be  due  to  the  cooling  the  blood  undergoes 
when  it  is  exposed  to  the  air,  for,  as  already  noted,  cold  retards 
coagulation,  while  heat  aids  it.  It  has  also  been  suggested  that 
the  fluid  condition  of  the  blood  in  the  circulation  is  due  to  its 
motion,  and  that  it  clots  when  it  comes  to  a  state  of  rest.  But 
experiment  shows  that  motion,  such  as  the  beating  of  blood  with 
wires,  hastens  coagulation. 

Experiments  demonstrate  that  the  fluidity  of  the  blood  is  main- 
tained only  when  the  blood  is  in  contact  with  the  normal  lining 
membrane  of  the  blood-vessels  :  when  this  relation  is  interrupted, 
either  by  disease,  or  by  death  or  injury  of  the  membrane,  or  by 
withdrawal  of  the  blood  from  the  vessel,  the  fluidity  ceases  and 
the  blood  coagulates. 

The  property  of  coagulation  possessed  by  blood  is  of  great 
service  in  arresting  hemorrhage.  There  are  individuals  in  whom 
bleeding,  which  in  most  people  would  be  only  slight,  amounts  to 
a  dangerous  hemorrhage,  often  requiring  surgical  skill  for  its 
arrest,  and  in  some  instances  being  so  uncontrollable,  even  by  the 
most  skilful  treatment,  that  death  results.  Such  persons  are 
called  bleeders,  and  on  them  surgeons  hesitate  to  perform  any  opera- 
tion, however  trivial,  the  extraction  of  a  tooth  even  being  often 


COAGULATION  OF  BLOOD.  297 

followed  by  an  alarming  loss  of  blood.  This  condition  is  spoken 
of  as  hemophilia  or  hemorrhagic  diathesis.  It  is  probable  that  in 
such  cases  the  fibrinogen  is  very  deficient. 

Theories  of  Blood-coagulation. — From  the  many  theories  which 
have  from  time  to  time  been  advanced  to  explain  this  process,  we 
shall  select  a  few,  each  of  which,  although  perhaps  not  now  held 
in  its  entirety,  still  has  elements  in  it  which,  combined  with  those 
of  other  theories,  enter  into  the  opinions  held  by  the  best  authorities 
in  regard  to  this  as  yet  unsolved  problem. 

All  explanations  have  as  their  basis  the  production  of  insoluble 
fibrin  from  soluble  fibrinogen,  but  as  to  how  this  change  comes 
about,  or  the  agencies  which  cause  it,  there  is  great  disagreement. 

Theory  of  Schmidt. — The  proteid  now  known  as  paraglobulin 
Schmidt  termed  fibrinoplastin,  and  in  his  theory  this  substance, 
under  the  influence  of  fibrin-ferment,  which  he  later  called 
thrombin,  enters  into  combination  with  fibrinogen,  the  result 
being  fibrin.  This  ferment  was  obtained  by  adding  alcohol  to 
blood-serum,  and  extracting  it  from  the  precipitate  by  water;  it 
was  destroyed  by  a  temperature  of  65°  C.,  and  had  the  power  of 
coagulating  a  considerable  amount  of  fibrinogen  ;  it  resembled, 
therefore,  the  ferments  or  enzymes,  and  was  considered  by  Schmidt 
to  belong  to  that  class.  He  later  considered  that  fibrinogen  was 
derived  from  paraglobulin. 

Theory  of  Hammarsten. — This  experimenter  demonstrated  that 
paraglobulin  takes  no  part  in  the  process  of  coagulation,  so  that 
at  the  present  time  it  does  not  enter  as  a  factor  into  any  of  the 
theories  of  blood-coagulation.  In  Hammarsten's  theory  there  are 
but  two  factors :  fibrinogen  and  fibrin-ferment.  The  action  of 
the  ferment  splits  the  fibrinogen  into  fibrin,  which  is  insoluble, 
and  fibrin-globulin,  which  remains  in  solution. 

Schmidt,  Hammarsten,  Freund,  Page's,  and  others  have  shown 
that  salts  of  calcium  play  a  very  important  part  in  the  coagulation 
process. 

Theory  of  Pekelharing. — This  theory  supposes  that  the  fibrin- 
ferment  of  Schmidt  is  composed  of  nucleo-albumin  and  calcium, 
and  that  the  calcium  leaves  the  nucleoproteid  and  unites  with 
fibrinogen,  the  compound  of  the  two  being  fibrin.  The  nucleo- 
albumin  comes  from  the  leukocytes  and  plaques,  but  does  not 
exist  in  normal  blood.  As  soon,  however,  as  blood  is  shed,  these 
cells  disintegrate,  with  the  result  of  setting  free  the  nucleoproteid. 
As  has  already  been  stated,  analyses  show  the  same  amount 
of  lime  in  fibrinogen  as  in  fibrin,  so  that  this  theory  cannot  be 
sustained. 

Theory  of  Lilienfeld. — The  originator  of  this  theory  attributes 
to  the  nucleoproteid  the  power  of  splitting  the  fibrinogen  into  a 
globulin  and  thrombosin,  which  latter  unites  with  lime  to  form 
fibrin.  He  regards  this  power  as  due  to  the  nucleic  acid,  and 


298  THE  BLOOD. 

states  that  acetic  or  any  other  weak  acid  will  effect  the  same 
change  in  fibrinogen.  This  theory  has  also  its  weak  points,  and 
there  is  great  doubt  whether  the  clot  is  fibrin  in  any  true  sense  of 
the  term.  Perhaps  we  can  in  no  better  way  present  to  our  readers 
the  present  status  of  this  subject,  which  is  at  best  unsatisfactory, 
than  by  giving  the  views  of  Schafer  in  his  Text-book  of  Physi- 
ology. The  evidence  seems  fairly  conclusive  that  three  factors  are 
essential  to  bring  about  coagulation  of  the  blood.  These  are 
fibrinogen,  the  nucleoproteid  prothrombin,  and  soluble  lime  salts, 
the  two  latter  acting  in  combination,  and  forming  Schmidt's  fibrin- 
ferment  or  thrombin.  In  the  normal  blood-vessels  the  prothrom- 
bin and  lime  have  not  entered  into  the  necessary  combination  or 
interaction  which  enables  them  to  act  as  a  ferment  upon  the 
fibrinogen.  This  nucleoproteid  prothrombin  cannot  by  itself  act  as 
a  ferment,  but  must  be  exposed  to  the  acting  soluble  lime  salts  ; 
it  does  not  follow,  however,  that  the  thrombin  is  a  compound  of 
the  nucleoproteid  and  lime ;  nor  is  there  any  certainty  as  to  just 
what  the  interaction  is.  The  prothrombin  doubtless  comes  from 
the  leukocytes  and  plaques ;  but  it  is  not  necessary  to  suppose 
that  they  always  undergo  disintegration  to  produce  it.  It  is  also 
probable  that  the  red  corpuscles  may  contribute  to  this  production 
of  nucleoproteids,  for  they  contain  them,  and  the  same  is  also 
true  of  the  epithelial  cells  of  the  blood-vessels,  which  are  doubt- 
less composed  of  living  protoplasm.  Schafer,  in  his  text-book, 
sums  up  the  evidence  as  to  coagulation  as  follows : 

1.  That  the  coagulation  of  blood — i.  e.,  the  transformation  of 
fibrinogen  into  fibrin — requires  for  its  consummation  the  inter- 
action of  a  nucleoproteid  (prothrombin)  and  soluble  lime  salts, 
and  the  consequent  production  of  a  ferment  (thrombin). 

2.  That  either  nucleoproteid  is  not  present  in  appreciable 
amount  in  the  plasma  of  circulating  blood,  or  that  the  interaction 
in  question  is  prevented  from  occurring  within  the  blood-vessels 
by  some  means  at  present  not  understood. 

3.  That  the  nucleoproteid  (prothrombin)  appears  and  the  inter- 
action occurs  as  soon  as  the  blood  is  drawn  and  is  allowed  to  come 
into  contact  with  a  foreign  surface,  the  source  of  the  nucleoproteid 
being  in  all  probability  mainly  the  leukocytes  (and  blood-platelets). 

4.  That  under  certain  circumstances  and  conditions  either  the 
nucleoproteid  does  not  appear  in  the  plasma  of  drawn  blood  or  it 
appears,  but  the  interaction  between  it  and  lime  salts  is  prevented 
or  delayed. 

5.  That  the  nucleoproteid  (prothrombin)  appears  in  the  plasma 
of  circulating  blood  under  certain  conditions,  being  in  all  probabil- 
ity shed  out  from  the  white  corpuscles  and  blood-platelets,  or  in 
some  cases  even  from  the  red  corpuscles ;  and  that  when  shed  out 
under  these  conditions  from  the  corpuscles,  or  when  artificially 
injected  into  the  vessels,,  it  tends  at  once  to  interact  with  the  lime 


REGENERATION  OF  BLOOD.  299 

salts  of  the  plasma  and  to  form  fibrin-ferment  (thrombin),  intra- 
vascular  coagulation  being  the  result. 

6.  That    under  other  conditions  either   the  shedding  out  of 
nucleoproteid  from  the  corpuscles  or  its  interaction  with  the  lime 
salts  of  the  plasma  may  be  altogether  prevented  and  the  blood 
rendered   incoagulable,  unless  nucleoproteid  is  artificially  added, 
or  unless  a  modification  of  the  conditions  is  introduced  which  will 
permit  of  the  interaction  of  the  nucleoproteid  with  lime  to  form 
ferment. 

7.  That  the  nucleoproteid  (prothrombin)  is  incompetent,  in  the 
entire  absence  of  lime  salts,  to  promote  the  transformation  of 
fibrinogen  into  fibrin  ;  but,  as  a  result  of  its  interaction  with  lime 
salts,  it  becomes  transformed  into  a  ferment  (thrombin),  which, 
under  suitable  conditions  of  temperature,  and  the  like,  produces 
fibrin. 

8.  That  either  the  place  of  nucleoproteid  in  coagulation  may 
be  taken  by  certain  albumoses,  such  as  those  found  in  snake-venom, 
and  by  certain  colloidal  substances,  such  as  those  prepared  by 
Grimaux  ;  or  that  such  substances  may  act  by  setting  free  nucleo- 
proteid from  the  leukocytes  and  other  elements  in  the  blood,  or 
from  the  cells  of  blood-vessels,  and  thus  indirectly  promote  coagu- 
lation. 

The  colloidal  substances  referred  to  in  paragraph  8  were  three  in 
number,  and  were  artificially  prepared  by  Grimaux,  and  presented 
many  of  the  characteristics  of  proteids.  They  all  gave  the  xantho- 
proteic  reaction  and  in  other  ways  resembled  the  proteid  class. 
Thus  when  injected  into  the  veins  of  animals,  as  the  dog,  cat,  or 
guinea-pig,  they  caused  intravascular  coagulation,  resembling  in 
this  respect  nucleoproteid.  It  is  suggested  by  Schafer  that  they 
produce  this  effect  not  directly,  but  by  setting  free  the  nucleo- 
proteid from  the  leukocytes,  inasmuch  as  there  is  no  disintegration 
of  the  red  or  white  corpuscles,  nor  any  apparent  change  in  the 
epithelium  of  the  vessels. 

Regeneration  of  Blood. — One  of  the  striking  peculiarities 
of  the  blood  is  the  rapidity  with  which  it  is  renewed  after  hemor- 
rhages. The  blood  constitutes  about  7.7  per  cent,  of  the  weight 
of  an  adult ;  and  it  is  estimated  that  a  hemorrhage  in  which  no 
more  than  3  per  cent,  of  the  weight  is  lost  will  not  be  fatal,  and 
that  the  plasma  will  be  renewed  in  such  cases  within  forty-eight 
hours,  although  it  may  require  weeks  for  a  renewal  of  the  red 
corpuscles.  In  the  treatment  of  severe  hemorrhages  it  is  now  the 
practice  to  inject  into  the  veins  physiologic  salt  solution  (p.  81). 
The  rationale  of  this  is  stated  by  Howell  to  be  that  in  normal 
blood  the  number  of  red  corpuscles  is  greater  than  that  necessary 
for  a  barely  sufficient  supply  of  oxygen,  and  that  if  after  a  hemor- 
rhage the  quantity  of  fluid  in  the  vessels  is  increased,  the  circula- 
tion is  made  more  rapid,  and  the  remaining  corpuscles  are  made 


300  THE  BLOOD. 

more  effective  as  oxygen-carriers ;  this  office  is  made  still  more 
effective  by  keeping  the  corpuscles  from  becoming  stagnant  in  the 
capillary  areas. 

In  proportion  as  intravenous  transfusion  of  salt  solution  has 
come  into  favor  for  the  treatment  of  hemorrhages,  in  a  similar 
proportion  has  transfusion  of  blood  been  abandoned.  From  what 
has  been  said,  it  will  readily  be  understood  that  in  the  withdrawal 
of  blood  from  the  vessels  of  a  lower  animal  or  man  the  conditions 
are  most  favorable  for  bringing  about  the  destruction  of  leuko- 
cytes, and  the  consequent  setting  free  of  the  nucleoproteid  pro- 
thrombin.  To  throw  this  material  into  the  circulation  of  a  living 
animal  is  to  invite  coagulation  within  the  vessels,  a  condition 
which  is  dangerous  in  the  extreme,  inasmuch  as  clots  would  be 
inevitably  carried  into  the  smaller  arteries  of  the  brain,  causing 
embolism.,  and  producing  a  fatal  result. 

It  has  also  been  demonstrated  that  the  injection  of  the  serum 
of  the  blood  of  some  animals  into  the  circulation  of  others,  as 
that  of  man  into  the  vascular  system  of  a  rabbit,  destroys  the  red 
corpuscles.  This  is  the  globuliddal  action  of  serum.  Such  a  result 
might  follow  in  the  case  of  blood-transfusion,  unless  special  care 
was  taken  to  select  an  animal  whose  blood  did  not  possess  this 
action  upon  the  blood  of  the  animal  on  which  the  operation  was 
to  be  performed. 

Hemolysis  and  Bacteriolysis. — The  fresh  normal  serum  of 
the  blood  of  a  goat,  an  ox,  a  dog,  etc.,  has  the  power  to  dissolve 
the  red  blood-cells  of  a  rabbit  or  guinea-pig.  This  is.  described  as 
the  normal  globuliddal  property  of  serum.  Such  serum  has  also 
the  power  of  dissolving  many  species  of  bacteria ;  this  is  its  bacte- 
ricidal property.  Buchner  attributed  both  of  these  to  a  substance 
existing  in  all  normal  serum,  to  which  he  gave  the  name  alexin. 
In  transfusing  blood,  therefore,  in  the  treatment  of  hemorrhage, 
the  danger  of  destroying  the  red  blood-cells  exists,  in  addition  to 
the  danger  already  mentioned.  It  should  be  said  that  Buchner's 
idea  of  alexin  has  been  much  modified  by  recent  researches ;  it  has 
been  shown  that  the  action  of  two  substances  is  necessary  to  bring 
about  hemolysis :  an  inter-body  and  a  complement,  the  latter  corre- 
sponding to  Buchner's  alexin.  This  was  shown  by  Ehrlich  and 
Morgenroth,  who  treated  the  blood  of  a  guinea-pig  with  the  serum 
of  a  dog,  the  complement  existing  in  the  guinea-pig  and  the  inter- 
body  in  the  dog. 

These  authorities  carried  their  observations  still  further  and 
found  that  normal  goat  serum  would  dissolve  the  red  cells  of  both 
guinea-pigs  and  rabbits,  and  that  in  this  serum  there  were  two 
inter-bodies,  one  for  the  red  cells  of  the  rabbit  and  the  other  for 
those  of  the  dog,  and  that  there  were  also  two  complements.  Ehr- 
lich believes  that  there  are  many  substances  of  similar  character 
existing  in  the  normal  serum  which  have  a  hemolytic  action. 


HEMOLYSIS  AND  BACTERIOLYSIS.  301 

Metchnikoff  and  Buchner  regard  the  leukocytes  as  being  the 
source  of  the  complements  or  alexins,  the  former  considering  them 
as  due  to  the  breaking  down  of  the  corpuscles,  the  latter  as  true 
secretory  products.  Other  authorities  regard  the  connection  between 
these  complements  apd  the  leukocytes  as  not  established.  Wasser- 
man  believes  the  leukocytes  to  be  one  source,  but  not  the  only  one, 
while  Ehrlich  and  Morgenroth  claim  that  the  production  of  the 
complements  is  one  of  the  functions  of  the  liver. 

Hemagglutinins  and  Bacterial  Agglutinins. — The  normal  serum 
of  the  goat  possesses  also  the  power  of  agglutinating  the  red  cells 
of  the  human  being,  the  pigeon,  and  the  rabbit — i.  e.,  causing  them 
to  adhere,  forming  clumps.  The  normal  serum  of  a  rabbit  will 
agglutinate  the  bacilli  of  typhoid  fever.  This  property  is  due  to 
substances  in  the  serum  called  agglutinins  ;  those  which  agglutin- 
ate the  red  cells  being  distinguished  as  hemagglutinins.  It  is 
believed  that  there  is  a  separate  agglutinin  for  each  species  of 
blood-cells.  The  hemolysins  and  the  agglutinins  are  not  identical 
substances,  for  a  serum  can  retain  its  agglutinating  power  after  its 
hemolytic  power  is  lost. 

Cytotoxins. — If  an  animal  is  injected  with  white  blood-cells, 
spermatozoa,  etc.,  substances  are  produced  in  its  serum  which  bring 
about  a  dissolving  action  in  the  cells  used  for  the  injection.  These 
substances  are  termed  cytotoxins.  Thus,  if  the  leukocytes  of  a  rab- 
bit are  injected  into  a  guinea-pig,  the  serum  of  the  guinea-pig  will 
dissolve  the  leukocytes  of  a  rabbit ;  in  this  instance  the  cytotoxin 
is  called  leukotoxim.  The  action  of  such  serum  is  believed  to  be 
due  to  interacting  substances,  as  in  the  case  of  hemolysis.  If  sper- 
matozoa are  injected,  a  cytotoxin  is  produced,  called  spermatoxin. 

Precipitins. — If,  instead  of  injecting  cells,  the  dissolved  albu- 
minous bodies  of  one  species  of  animal  are  injected  into  another, 
there  is  a  precipitation  of  albumin.  Thus,  if  a  rabbit  is  injected 
with  the  serum  of  a  horse,  and  subsequently  the  rabbit  serum  is 
mixed  with  that  of  a  horse,  the  mixture  becomes  cloudy,  owing  to 
the  precipitation  of  the  horse's  albumin.  The  substances  which 
produce  this  precipitation  are  termed  precipitins. 

A  practical  application  has  been  made  of  the  knowledge 
obtained  by  this  research  into  the  nature  of  precipitins  in  the 
identification  of  blood-stains.  For  the  details  of  the  method  the 
reader  is  referred  to  text-books  treating  of  the  subject.  Ewing 
states  that  the  reaction  does  not  fail  with  very  old  specimens  of 
blood,  although  it  becomes  less  distinct  the  older  the  specimen. 
Ziemke  obtained  a  cloudiness  in  three  hours  from  a  blood-stain 
twenty-five  years  old ;  from  blood  mixed  with  earth  three  years 
old  ;  from  decomposed  blood  ;  and  from  human  blood  highly  diluted 
with  six  other  kinds  of  blood.  A  solution  of  iron  rust  gave  no 
reaction.  Uhlenmuth  secured  positive  results  with  blood  of  a  three 
months7  decomposed  cadaver.  Stern  obtained  the  characteristic 
reaction  in  solutions  of  1  of  serum  to  50,000  of  blood.  Ewing 


302 


LYMPH. 


concludes  his  discussion  of  the  subject,  in  his  Clinical  Pathology  of 
the  Blood,  as  follows  :  "  From  the  foregoing  discussion  it  is  evident 
that  full  medicolegal  requirements  for  the  positive  identification 
of  blood-stains  may  be  met,  under  some  conditions,  by  the  biologic 
test.  These  conditions  are  the  positive  proof  by  the  hemin  test 
that  the  material  is  blood,  and  the  occurrence  of  a  flocculent  pre- 
cipitate appearing  within  one  to  three  hours  in  the  suspected  speci- 
men and  in  no  other  of  the  controls  when  a  potent  serum  is  added 
in  proportion  of  1 : 50  of  blood. 

"  While  these  conditions  can  usually  be  secured  when  dealing 
with  fresh  blood  in  considerable  quantities,  in  the  writer's  opinion 
and  experience  the  material  submitted  for  medicolegal  examination 
is  more  apt  to  be  old,  scanty,  and  impure,  and  the  difficulty  of 
securing  a  fully  satisfactory  test  by  this  method  is  thereby  greatly 
increased.  With  such  material  one  has  often  to  be  content  with 
faint  turbidities  instead  of  flocculent  precipitates,  and  in  such  cases 
it  would  appear,  as  Stoenesco  maintains,  that  a  guarded  opinion  be 
given  and  the  claim  made  only  that  the  specimen  is  probably  human 
blood.  It  should  be  added  that  an  absolutely  faultless  technic  is 
required,  and  that  this  can  be  obtained  only  after  considerable 
experience." 

LYMPH. 

Lymph  is  an  alkaline  fluid  which  is  derived  from  the  blood, 
and  while,  generally  speaking,  its  constituents  are  the  same  as 
those  of  the  plasma,  still  these  differ  in  amount  to  a  considerable 
degree  ;  nor  is  the  lymph  obtained  from  all  parts  of  the  body 
uniform  in  composition. 

Chemical  Composition  of  I/ymph. — The  following  anal- 
ysis is  of  lymph  obtained  from  a  case  of  fistula  of  the  thoracic 
duct  in  man,  and  is  reported  by  Munk  and  Rosenstein.  In  100 
parts  of  lymph  there  are  : 

Total  solids 3.7      to  5.5 

Proteids 3.4      "4.1 

Substances  soluble  in  ether 0.046"  0.13 

Sugar  (dextrose) 0.1 

Salts 0.8       "0.9 

In  another  specimen  the  inorganic  constituents  were  found  by 
Hensler  and  Danhardt  to  be  : 


Nad 0.614 

Na2O 0.057 

K2O 0.049 

CaO  0.013 


MgO 
Fe203 

So 


.  traces 
0.033 


From  lymph  only  0.1  per  cent,  of  fibrinogen  can  be  obtained, 
while  from  plasma  the  amount  obtainable  is  0.4  per  cent.  Besides 
fibrinogen,  paraglobulin  and  serum-albumin  are  also  present. 


ORIGIN  OF  LYMPH.  303 

Lymph  coagulates  more  slowly  than  the  blood,  and  the  clot  is  less 
firm.  Urea  is  present  to  a  greater  amount  than  in  plasma. 

Histologic  Composition  of  I/ymph. — Examined  under 
the  microscope  lymph  is  found  to  contain  colorless  cells,  lympho- 
cytes, which  pass  into  the  blood  with  the  lymph  and  there  become 
leukocytes  (p.  291).  Fat-globules  are  also  found,  especially  after 
a  meal,  and  in  the  lymph  from  the  thoracic  duct. 

Origin  of  I/ymph. — While  there  is  no  doubt  that  the  source 
of  the  lymph  is  the  blood,  still  there  is  a  difference  of  opinion  as 
to  the  manner  in  which  it  escapes  from  the  blood-vessels. 

Theory  of  Ludwig. — Ludwig  believed  that  the  pressure  of  the 
blood  in  the  capillaries  was  sufficient  to  cause  the  plasma  to  filter 
through  their  walls,  thus  forming  the  lymph.  He  also  believed 
that  diffusion  played  a  part  in  lymph-formation.  He  expressed 
his  views  as  follows  :  "  The  blood  which  is  contained  in  the  vessels 
must  always  tend  to  equalize  its  pressure  and  its  chemical  con- 
stitution with  those  of  the  extravascular  fluids,  which  are  only 
separated  from  it  by  the  porous  blood-vessel  walls.  If,  for  ex- 
ample, the  quantity  of  blood  in  the  vessels  has  increased,  the  mean 
blood-press.ure  is  also  increased,  and  at  once  a  portion  of  the  blood 
is  driven  out  into  the  tissues  by  a  mere  process  of  filtration.  The 
same  result  is  brought  about  when  the  constitution  of  the  blood  is 
altered  by  the  absorption  of  food  or  by  increased  excretion  by  the 
kidneys,  blood,  or  skin,  or  when  the  composition  of  the  tissue- 
fluids  is  altered  in  consequence  of  increased  metabolic  changes 
taking  place  in  the  tissues.  In  the  latter  case  the  changes 
brought  about  in  the  lymph  are  effected  by  processes  of  diffusion." 
This  theory  of  Ludwig  may,  therefore,  be  termed  that  of  filtration 
and  diffusion. 

Theory  of  Heidenhain. — This  experimenter  studied  the  subject 
of  lymph-formation  by  examining  the  flow  from  the  thoracic 
duct.  He  found  that  if  the  thoracic  aorta  was  obstructed,  there 
would  follow  a  fall  of  arterial  blood-pressure  below  the  obstruc- 
tion, and  yet  there  was  no  diminution  in  the  flow  of  lymph  in  the 
thoracic  duct,  and  in  some  cases  it  was  increased.  If  lymph  was 
formed  by  filtration  from  the  blood,  a  diminution  of  blood-pressure 
should  have  been  followed  by  a  corresponding  lessening  of  lymph- 
production.  Other  experiments  demonstrated  that  the  flow  of 
lymph  might  be  increased  without  correspondingly  increasing  the 
blood-pressure.  He  also  found  that  if  commercial  peptone  and 
some  other  substances  were  injected  into  the  blood-circulation,  the 
amount  and  concentration  of  the  lymph  would  be  increased,  al- 
though blood -pressure  might  be  reduced  ;  also  that  if  concentrated 
solutions  of  sodium  chlorid  or  sugar  were  injected,  the  flow  of 
lymph  would  be  increased  and  its  concentration  diminished.  If 
blood-pressure  was  increased,  it  was  so  but  slightly.  Heidenhain 
terms  substances  having  the  power  of  increasing  the  flow  of  lymph 
lymphagogues.  These  experiments  demonstrated  that  the  lymph 


304  LYMPH. 

may  contain  more  of  injected  substances  than  the  blood-plasma, 
while  at  the  same  time  there  is  no  increase  in  blood-pressure. 
From  these  experiments  Heidenhain  formed  the  opinion  that 
filtration  and  diffusion  cannot  explain  all  the  facts  connected  with 
the  formation  of  lymph,  but  that  it  is  to  be  attributed  to  a  selective 
power  of  the  endothelial  cells  of  the  walls  of  the  capillaries,  and 
that  lymphagogues  act  by  stimulating  these  cells. 

This  subject  has  been  investigated  by  Starling,  who  finds  many 
reasons  for  upholding  the  theory  of  Ludwig  as  against  that  of 
Heidenhain.  For  a  full  discussion  of  the  subject  we  must  refer 
our  readers  to  Schafer's  Physiology,  but  it  will  not  be  out  of  place 
to  quote  Starling's  conclusions.  He  says  : 

"  Thus  a  renewed  investigation  of  the  facts  discussed  by  Heiden- 
hain has  shown  that  they  are  not  irreconcilable  with  the  filtration 
hypothesis,  but  rather  serve  to  support  it.  At  the  same  time  they 
prove  the  extreme  importance  of  the  factor  upon  which  so  much 
stress  was  laid  by  Cohnheim,  namely,  the  nature  of  the  filtering- 
membrane.  In  fact,  we  may  say  that  the  formation  of  lymph  and 
its  composition,  apart  from  the  changes  brought  about  by  diffusion 
and  osmosis  between  it  and  the  tissues  it  bathes,  depend  entirely 
upon  two  factors  :  1.  The  permeability  of  the  vessel- wall.  2.  The 
intracapillary  blood-pressure. 

"  So  far  as  our  experimental  data  go,  we  have  no  sufficient 
evidence  to  conclude  that  the  endothelial  cells  of  the  capillary 
walls  take  any  active  part  in  the  formation  of  lymph.  It  seems 
rather  that  the  vital  activities  of  these  cells  are  devoted  entirely 
to  maintaining  their  integrity  as  a  filtering-membrane,  differing  in 
permeability  according  to  the  region  of  the  body  in  which  they 
may  be  situated.  Any  injury,  whether  from  within  or  without, 
leads  to  a  failure  of  this  their  one  function,  and  therefore  to  an 
increased  permeability,  with  the  production  of  an  increased  flow 
of  a  more  concentrated  lymph. 

"We  have  no  evidence  that  the  nervous  system  has  any  in- 
fluence on  the  production  of  lymph  in  any  part,  except  an  indirect 
one  by  altering  the  capillary  pressures  in  the  part  through  the 
intermediation  of  vasoconstrictor  or  dilator  fibers.  This  action  is 
better  marked  in  situations  where  the  capillaries  are  normally 
very  permeable  or  where  the  permeability  has  been  increased  by 
local  injury  to  the  vessels,  or  by  the  circulation  of  poisons  in  the 
blood -stream." 

The  lymph-corpuscles  enter  the  lymph  as  it  passes  through  the 
lymphatic  glands  or  other  lymphoid  tissue,  such  as  the  tonsils  and 
the  thymus  gland,  and  become  constituents  of  the  lymph. 

Office  of  the  Lymph. — The  lymph  after  it  passes  out  from 
the  blood-vessels  bathes  the  tissues,  and  is  one  of  their  sources  of 
nutrition,  but  not  the  only  one,  for  there  is  abundant  evidence  that 
tissues  may  receive  their  nutritive  supply  directly  from  the  blood 
and  pass  into  that  fluid  their  waste-products.  This  muscles  will 


PLATE  n. 


A,  aorta,  with  left  vagus  and  phrenic  nerves  crossing  its  transverse  arch  ; 
B,  root  of  pulmonary  artery ;'  C,  right  ventricle  ;  D,  right  auricle ;  E,  vena  cava 
superior,  with  right  phrenic  nerve  on  its  outer  border;  F,' F,  right  and  left  lungs 
collapsed,  and  turned  outward  to  show  the  heart's  outline;  G,  inferior  vena  cava ; 
H,  celiac  axis,  dividing  into  the  gastric,  splenic,  and  hepatic  arteries  (Maclise). 


THE  HEART.  305 

do,  while  at  the  time  no  lymph  is  flowing  in  the  lymphatic  vessels 
of  the  part.  When  lymph  accumulates,  whether  in  a  serous 
cavity  or  in  the  cellular  tissue  beneath  the  skin,  it  constitutes 
dropsy  or  edema. 

The  lymph  is  collected  by  the  lymphatic  vessels  and  ultimately 
reaches  the  blood-circulation  again  (p.  330). 

CHYLE. 

The  term  chyle  is  applied  to  that  portion  of  the  lymph  which 
comes  from  the  small  intestine  during  the  period  of  digestion. 
The  tissues  of  this  portion  of  the  body  are,  like  all  others,  bathed 
in  lymph ;  but  during  digestion  such  products  as  enter  the  lacteals 
change  its  composition  to  a  considerable  extent,  and  the  fat  gives 
to  it  a  milky  appearance.  The  following  is  an  analysis  of  chyle 
taken  from  a  fistula  of  the  thoracic  duct  in  man  (Paton) : 

Water 95.34- 

Proteids 1.37 

Fats 2.40 

Cholesterin , 0.06 

Lecithin     .    .    . , 0.03 

Inorganic  constituents 0.56 

CIRCULATORY  SYSTEM. 

The  blood  in  carrying  nutrition  to,  and  in  carrying  waste 
products  from,  the  tissues  passes  through  the  entire  circulatory 
system,  and  this  constitutes  the  circulation  of  the  blood.  Before 
studying  this  process  in  detail  it  is  essential  to  have  a  knowledge 
of  the  organs  concerned  in  carrying  it  on-^i.  e.,  the  circulatory 
organs.  These  are  (1)  the  heart,  (2)  the  arteries,  (3)  the  capillaries, 
and  (4)  the  veins. 

THE  HEART. 

The  heart,  together  with  the  great  blood-vessels  at  its  base,  is 
enclosed  in  the  pericardium,  a  fibroserous  membrane  having  an 
external  fibrous  and  an  internal  serous  layer.  The  serous  layer 
not  only  lines  the  inner  surface  of  the  sac,  forming  the  parietal 
portion,  but  it  also  covers  the  heart  itself;  this  portion  is  the 
visceral  portion  or  epicarditim ;  its  structure  is  similar  to  that 
of  other  serous  membranes,  being  composed  of  connective  tissue 
and  elastic  fibers,  beneath  which  are  the  blood-vessels,  nerves,  and 
lymphatics  of  the  heart. 

The  myocardium,  or  muscular  structure  of  the  heart,  is 
composed  of  transversely  striated  muscular  fiber-cells,  each'  con- 
taining a  single  nucleus.  They  differ  from  voluntary  muscle  in 
possessing  no  sarcolemma,  in  branching  and  uniting  with  adjoining 
cells,  and  in  having  their  striae  less  pronounced  (p.  61). 

The  endocardium,  which  lines  the  heart  and  takes  part  in 
the  formation  of  the  valves,  resembles  the  epicardium  in  struct- 
ure, and  is  covered  by  endothelium. 


306 


CIRCULATORY  SYSTEM. 


The  heart  (Figs.  157,  158)  is  a  hollow  muscular  organ  whose 
functions  consist  in  acting  as  a  reservoir  and  also  as  a  pump,  the 
auricles  being  the  reservoir  and  the  ventricles  being  the  pump 
(Plate  2).  It  is  about  12.5  cm.  long,  8  cm.  wide  in  its  widest 
part,  and  6.3  cm.  thick  at  its  thickest  part ;  its  weight  is  about 
300  grams  in  the  adult.  It  has  a  conical  form,  its  base  being 
above  and  to  the  right,  and  its  apex  below  and  to  the  left.  It  is 

divided  longitudinally  by  a 
partition  or  septum  into  a 
right  and  a  left  half,  which 
are  sometimes  denominated 
the  right  heart  and  the  left 
heart.  Each  half  is  com- 
posed of  an  auricle  and  a 
ventricle ;  thus  there  are 
four  cavities — the  right  au- 
ricle, the  right  ventricle,  the 
left  auricle,  and  the  left  ven- 
tricle. 

The  right  auricle  (Fig. 
157)  is  somewhat  larger  than 
the  left,  and  has  the  thinnest 
walls  of  the  four  cavities, 
measuring  about  2  mm.  in 
thickness.  Discharging  into 
this  cavity  are  the  superior 
and  inferior  venae  cavae,  at  the 
mouths  of  which  there  are  no 
valves.  Within  the  cavity  is 
the  Eustachian  valve,  which 
will  further  be  described 
when  discussing  the  fetal  cir- 
culation, This  valve  is  sit- 
uated between  the  opening 
of  the  inferior  vena  cava  and 
the  auriculoventricular  orifice. 
The  right  ventricle  (Fig. 


FIG.  157. — Interior  of  right  auricle  and 
ventricle,  exposed  by  the  removal  of  a  part 
of  their  walls :  1,  superior  vena  cava ;  2,  in- 
ferior vena  cava ;  2',  hepatic  veins  ;  3, 3',  3". 
inner  wall  of  right  auricle  ;  4,  4,  cavity  of 
right  ventricle ;  4',  papillary  muscle  ;  5, 5',  5", 
flaps  of  tricuspid  valve;  6,  pulmonary  ar- 
tery, in  the  wall  of  which  a  window  has 
been  cut ;  7,  on  aorta  near  the  ductus  arte- 
riosus ;  8,  9,  aorta  and  its  branches ;  10,  11, 
left  auricle  and  ventricle  (Allen  Thomson). 


1 57)  has  walls  whose  thickness 

is  greater  than  that  of  either  auricle,  but  less  than  that  of  the  left 
ventricle.  The  cavity  of  the  right  ventricle  communicates  with 
that  of  the  right  auricle  by  the  right  auriculoventricular  orifice, 
at  which  is  situated  the  tricuspid  valve.  It  ordinarily  contains, 
when  filled,  87  grams  of  blood  (p.  314).  Connected  with  this 
ventricle  is  the  pulmonary  artery,  at  whose  point  of  junction  with 
the  ventricle  is  the  pulmonary  orifice,  at  which  is  situated  the  pul- 
monary valve. 

The  left  auricle  (Fig.  158)  is  not  so  large  as  the  right,  but  its 
walls  are  thicker.     Discharging  into  it  are  the  two  right  and  the 


THE  HEART. 


307 


two  left  pulmonary  veins,  the  former  coming  from  the  right  and 
the  latter  from  the  left  lung.  The  left  veins  sometimes  join,  and 
have  but  a  single  opening,  in  which  case  there  would,  of  course, 
be  but  three  openings  instead  of  four.  At  these  openings  there 
are  no  valves. 

The  left  ventricle  (Fig.  158)  is  by  far  the  most  powerful  of  the 
four  subdivisions  of  the  heart.  Its  walls  are  three  times  as  thick 
as  those  of  the  right  ventricle.  The 
capacity  of  its  cavity  is  the  same  as 
that  of  the  right.  The  left  auricle  and 
ventricle  communicate  by  the  left 
auriculoventricular  orifice,  at  which  is 
situated  the  mitral  valve.  Connected 
with  this  ventricle  is  the  aorta,  the 
opening  of  communication  being  the 
aortic  orifice,  at  which  is  situated  the 
aortic  valve. 

On  the  inner  surface  of  the  ventri- 
cles the  muscular  tissue  projects,  and 
forms  the  eolunmce  camece,  or  fleshy 
columns ;  some  of  these  are  ridges 
only,  while  others  are  attached  at  both 
ends,  but  are  unattached  in  the  middle, 
while  still  others  project  into  the 
cavity  and  are  attached  at  one  ex- 
tremity only ;  the  latter  are  the  mus- 
culi  papillares,  or  papillary  muscles. 

Cardiac  Valves. — There  are  four 
sets  of  valves  in  the  heart :  (1)  The 
tricuspid  ;  (2)  the  pulmonary  ;  (3)  the 
mitral ;  and  (4)  the  aortic.  The  pulmo- 
nary and  aortic  valves  are  sometimes 
spoken  of  as  the  semilunar  valves. 

The  tricuspid  valve  (Fig.  159)  is 
situatrd  at  the  right  auriculoventric- 
ular orifice,  and,  as  its  name  implies, 
consists  of  three  cusps  or  segments. 
The  bases  of  these  cusps  are  attached  to 
the  opening,  while  the  other  edges  are 
free,  and  to  them  are  attached  the  chordae  tendinece,  or  tendinous  cords, 
the  other  ends  being  connected  with  the  free  extremities  of  the 
musculi  papillares  to  which  reference  has  been  made.  This  valve, 
when  shut,  closes  the  right  auriculoventricular  orifice ;  when 
open  the  segments  are  in  the  cavity  of  the  right  ventricle.  The 
tendinous  cords  prevent  these  segments  from  passing  into  the  cav- 
ity of  the  auricle  at  the  time  of  the  valve's  closure,  while  the  papil- 
lary muscles  by  their  shortening  keep  the  cords  taut  at  the  time  of 
the  ventricle's  contraction,  as  will  be  seen  later. 


FIG.  15S. — Left  auricle  and  ven- 
tricle, opened  and  part  of  their 
walls  removed  to  show  their  cavi- 
ties ;  1,  right  pulmonary  vein  cut 
short;  1',  cavity  of  left  auricle; 

3,  3",  thick  wall  of  left  ventricle  ; 

4,  portion  of  the  same  with  papil- 
lary muscle  attached  ;  5,  the  other 
papillary  muscles;  6,  6',  the  seg- 
ments of  the  mitral  valve ;  7,  the 
figure  in  aorta  is  placed  over  the 
semilunar  valves;    8,  pulmonary 
artery ;  10,  aorta  and  its  branches 
(Allen  Thomson). 


308 


CIRCULATORY  SYSTEM. 


The  pulmonary  valve  is  sometimes  spoken  of  as  the  pulmonary 
semilunar  valve  or  valves.  It  is  composed  of  three,  occasionally 
two,  segments,  and  is  situated  at  the  beginning  of  the  pulmonary 

artery.  These  segments  are  at- 
tached at  their  bases  to  the  wall  of 
the  artery,  and  on  the  free  edge  of 
each  is  a  projection,  the  corpus 
Arantii.  When  the  valve  is  open 
the  segments  lie  against  the  walls 
of  the  artery ;  when  it  is  shut  they 
are  in  contact,  and  thus  close  the 
orifice  of  the  pulmonary  artery. 

The  mitral  valve  is  sometimes 
described  as  the  bicuspid,  because 
it   consists    of    two    cusps.     The 
attachments  of  the  segments,  the 
FIG.  159.-0rifice  of  the  heart,  seen    pregence  of  chordse,  and  the  other 


points    referred    to    in 


from  above,  both  the  auricles  and  the 

great  vessels  being  removed :  PA,  pul-  anatomic 

monary    artery      and     its    semilunar  speaking    of    the    tricuspid    Valve 

valves;     AO,    aorta    and    its    valves;  "            &               .                   *  .            .  . 

RA V,  tricuspid,  and  LAV,  bicuspid   are  to  be  seen  in  connection  with 

valves;  MV,  segments  of  mitral  valve  ;    t^e  mitral.      It   closes   the  auricu- 
LV,     segments     of     tricuspid     valve    ,  ,    .      ,  .« 

(Huxley).  loventncular  orifice. 

The  aortic  valve  resembles  in 

all  essential  particulars  the  pulmonary ;  it  likewise  is  sometimes 
called  the  semilunar  valve,  and  closes  the  aortic  orifice. 

The  ventricular  septum  is  the  partition  between  the  right 
and  left  ventricles.  It  is  closed  at  all  periods  of  life.  The 
auricular  septum,  between  the  auricles,  is  closed  from  the  tenth 
day  after  birth ;  prior  to  this  time  and  during  fetal  life  it  has  an 
opening,  the  foramen  ovale,  which  serves  as  a  means  of  communi- 
cation between  the  right  and  the  left  auricles. 

Structure  of  the  Valves. — The  valves  consist  of  reduplications 
of  endocardium,  between  which  is  fibrous  tissue. 

THE  ARTERIES, 

Arteries  are  composed  of  three  coats  :  (1)  An  internal,  tunica 
intima;  (2)  a  middle,  tunica  media;  and  (3)  an  external,  tunica 
adventitia. 

The  tunica  intima  consists  of  a  layer  of  pavement-epithelium 
(Fig.  160),  the  cells  being  polygonal,  oval,  or  fusiform,  termed 
endothelium,  and  of  a  network  of  elastic  fibers  or  a  fenestrated 
membrane  (Fig.  161).  Between  these  two  layers  is  a  subepithelial 
layer  consisting  of  connective  tissue. 

The  tunica  media  has  a  special  physiologic  interest.  In  the 
large  arteries — that  is,  those  larger  than  the  carotids — this  coat  is 
principally  yellow  elastic  tissue,  only  about  one-fourth  being  mus- 
cular tissue.  Vessels  of  this  size  are  therefore  characterized  by 


THE  ARTERIES. 


309 


their  elasticity.  In  the  arteries  of  medium  size — that  is,  those 
between  the  carotids  and  those  having  a  diameter  of  about  2  mm. 
— the  amount  of  muscular  tissue  is  very  much  increased,  while  the 


Endothelium  of  the 

intima. 
"  Intima. 

Media. 


Adventitia  with 
non-striated  mug- 
cle-fibers  in  cross- 
section. 


FIG.  160. — Section  through  human  artery,  one  of  the  smaller  of  the  medium-sized ; 
X  640  (Bohm  and  Davidoff ). 

elastic  tissue  is  also  well  represented.  Such  arteries  possess,  there- 
fore, both  contractility  and  elasticity.  In  the  small  arteries — that 
is,  those  less  than  2  mm.  in  diameter — the  external  coat  gradually 

Intima. 
—  Elastica  in- 
v         terna. 

Endothelium  of 
the  intima. 


m.  >     Media. 


Fenestrated 

?§?•• — | —     elastic    mem- 
brane. 

Elastica  ex- 

terna. 

Inner  layer  of 
adventitia. 


Outer  layer  of 
adventitia. 


~- —  —  Vasa  vasorum. 


FiG.  161. — Cross-section  of  the  human  carotid  artery  ;  X  150  (Bohm  and  Davidoff). 

disappears  until  in  the  arterioles  there  remains  only  muscular 
tissue,  representing  the  middle  coat  and  the  internal  coat.  These 
vessels  are  endowed  with  the  property  of  contractility. 


310  CIRCULATORY  SYSTEM. 

The  tunica  adventitia  consists  of  bundles  of  white  connective 
tissue  and  elastic  fibers,  and  gives  to  the  artery  its  strength.  This 
coat  merges  with  the  sheath  of  the  artery,  which  is  composed  of 
fibro-areolar  tissue,  and  in  this  are  the  blood-vessels  which  supply 
the  arteries,  the  vasa  vasorum. 

THE  CAPILLARIES, 

The  capillaries  are  minute  vessels,  having  in  general  a  diameter 
of  12  f2j  though  this  differs  very  considerably  in  the  different 
organs  of  the  body.  They  are  smallest  in  the  brain  and  intestinal 
mucous  membrane,  and  largest  in  the  skin  and  bone-marrow, 
where  they  have  a  diameter  of  about  20  //. 

Their  arrangement  is  also  subject  to  great  variation  ;  thus  in  the 
lungs  and  mucous  membranes  they  form  rounded  meshes,  while  in 
muscles  and  nerves  the  form  of  the  mesh  is  elongated.  In  some 
organs  they  are  very  close  together,  as  in  the  lungs,  while  else- 
where they  are  separated  to  a  considerable  extent,  as,  for  instance, 
in  the  external  coats  of  arteries.  In  general,  where  an  organ  is 
active,  as  is  the  kidney,  there  the  number  of  capillaries  is  the 


FIG.  162. — Endothelial  cells  of  capillary  (a)  and  precapillary  (b)  from  the  mesentery 
of  a  rabbit;  stained  in  silver  nitrate  (Huber). 

greatest ;  and  where  it  is  inactive,  as  is  the  case  with  bone,  the 
capillaries  are  correspondingly  lacking. 

The  walls  of  the  capillaries  consist  of  endothelial  cells  joined 
edge  to  edge  by  a  cement-material. 

From  a  physiologic  standpoint  this  portion  of  the  circulatory 
apparatus  is  the  most  important,  as  all  the  changes  between  the 
blood  and  the  tissues  take  place  while  the  blood  is  passing  through 
the  capillaries. 

THE  VEINS. 

The  structure  of  the  veins  is  in  many  respects  similar  to  that 
of  the  arteries.  They  are  likewise  composed  of  three  coats,  but 


CIRCULATION  OF  THE  BLOOD.  311 

the  middle  coat  is  the  thinnest — so  much  so,  indeed,  that,  while 
the  arteries  when  cut  remain  patulous,  the  veins  collapse.  This 
coat  contains  both  elastic  and  fibrous  tissue :  the  former  gives 
the  vessels  some  elasticity,  while  to  the  latter  is  attributable  the 
greater  strength  of  the  veins  as  compared  with  the  arteries.  The 
greater  thickness  of  the  arterial  wall  would  seem  calculated  to 
make  these  vessels  the  stronger,  but,  although  possessed  of  thin 
walls,  still  the  white  fibrous  tissue  which  aids  in  their  formation 
gives  the  veins  greater  resisting  power.  Valves  are  to  be  found 
in  most  of  the  veins,  but  are  absent  in  those  whose  diameter  is 
less  than  2  mm. ;  also  from  the  vena  cava,  hepatic,  portal,  renal, 
uterine,  ovarian,  cerebral,  spinal,  pulmonary,  and  umbilical  veins. 
The  valves  are  so  arranged  that  they  permit  the  blood  to  flow  in 
the  direction  of  the  heart,  but  prevent  its  flow  in  the  opposite 
direction.  They  consist  of  a  reduplication  of  the  internal  coat, 
together  with  connective  and  elastic  tissue  to  give  them  strength. 
Like  the  arteries,  they  are  supplied  with  vasa  vasorum  to  nourish 
their  walls. 

CIRCULATION  OF  THE  BLOOD. 

The  course  of  the  blood,  starting  from  any  point,  may  be 
traced  through  the  circulatory  apparatus.  The  circulation  from 
the  right  ventricle  through  the  lungs  and  back  to  the  left  side  of 
the  heart  is  the  lesser  or  pulmonary  circulation  ;  that  from  the  left 
ventricle  through  the  rest  of  the  body  other  than  the  lungs  and 
back  to  the  right  side  of  the  heart  is  the  greater  or  systemic  circu- 
lation. Beginning  with  the  right  auricle,  the  blood  flows  into  this 
cavity  from  the  venae  cavse  (inferior  and  superior) ;  thence  through 
the  right  auriculoventricular  orifice  into  the  right  ventricle ;  thence 
into  and  through  the  pulmonary  artery  to  the  lungs ;  thence  by  the 
pulmonary  veins  into  the  left  auricle ;  thence  through  the  left  auric- 
uloventricular orifice  into  the  left  ventricle ;  thence  into  and 
through  the  aorta  and  the  arterial  system  to  the  capillaries; 
through  these  vessels  to  the  vein^,  by  which,  through  the  venae 
cava3,  it  returns  to  the  right  auricle,  the  place  of  beginning. 

Cardiac  Movements. — If  the  heart  is  exposed  in  a  living 
animal — a  dog,  for  example — it  will  be  seen  that  the  ventricles 
are  at  one  time  in  motion  and  at  another  time  at  rest.  Each 
period  of  motion  and  rest  constitutes  a  pulsation  or  a  cardiac  cycle, 
and  these  pulsations  recur  very  rapidly,  so  much  so  that  the  inter- 
vals are  recognized  with  difficulty.  These  different  states  of  the 
heart  are  better  detected  by  the  sense  of  touch  than  by  that  of 
sight.  If  the  ventricles  are  grasped  by  the  hand,  it  will  be  found 
that,  corresponding  with  the  resting  stage,  the  muscular  tissue 
composing  them  is  soft  and  flaccid,  while  during  the  active  stage 
it  is  hard  and  resisting.  If  these  movements  are  studied  still  more 
carefully  and  analyzed,  it  will  be  found  that  the  beginning  of  the 


312  CIRCULATORY  SYSTEM. 

cardiac  movement,  which  immediately  follows  the  stage  of  rest, 
occurs  in  the  auricles,  in  the  region  of  the  openings  of  the  vense 
cavae  on  the  right  side,  and  of  the  pulmonary  veins  on  the  left ; 
that  this  movement  is  propagated  along  the  auricles  in  the  direc- 
tion of  the  ventricles ;  and  that  by  the  time  it  has  reached  the 
auriculo ventricular  orifices  it  has  ceased  at  the  orifices  of  the 
veins,  and  the  muscular  tissue  in  this  region  has  begun  to  relax. 
It  is  to  be  noted  that  the  auricles  act  synchronously,  so  that 
whatever  is  the  condition  of  one  auricle  as  to  relaxation  or  con- 
traction of  its  muscular  tissue,  the  same  condition  exists  in  the 
other.  This  contraction  of  the  auricles  is  spoken  of  as  the 
auricular  systole,  and  has  something  of  a  peristaltic  character, 
which  has  already  been  studied  in  connection  with  the  stomach 
and  small  intestine,  although  differing  materially  in  that  it  is  much 
more  rapid. 

Up  to  this  time  the  ventricles  are  relaxed,  or  in  a  condition 
of  diastole;  but  as  soon  as  the  auricular  contraction  reaches 
the  ventricles  these  organs  take  it  up,  although  in  a  different 
manner.  For,  while  in  the  auricles  one  portion  is  contracting 
while  another  is  relaxing,  in  the  ventricles  the  whole  mass  of 
muscle  contracts  at  once  with  a  degree  of  suddenness  and  vigor 
which  might  be  expected  of  so  large  a  mass  of  striped  muscular 
tissue.  This  contraction  is  the  ventricular  systole,  and  while  it  is 
taking  place  the  auricles  are  relaxing  throughout ;  this  relaxation 
constitutes  the  auricular  diastole.  Thus  the  auricular  systole  and 
ventricular  diastole,  and  the  auricular  diastole  and  ventricular 
systole,  are  respectively  synchronous.  Immediately  after  the 
systole  of  the  ventricles  these  structures  relax,  and  for  a  brief 
period  the  whole  heart,  both  auricles  and  both  ventricles,  is  in  a 
state  of  relaxation ;  this  is  the  pause  of  the  heart.  The  work 
performed  by  the  ventricles  is  so  much  more  important  than  that 
of  the  auricles  that  when  the  terms  systole  and  diastole  are  used, 
reference  is  always  had  to  these  states  of  the  ventricles,  the 
auricles  being  practically  ignored.  To  designate  the  corresponding 
states  of  the  auricles  it  is  always  necessary  to  speak  of  the  auricular 
systole  and  diastole. 

Cardiograph. — The  cardiograph  is  an  instrument  for  recording 
the  movements  of  the  heart,  the  record  itself  being  a  cardiogram. 
The  form  most  used  is  that  of  Marey.  It  consists  of  a  metal 
box,  over  the  mouth  of  which  an  elastic  membrane  is  stretched, 
to  which  a  knob  is  attached  (Fig.  163).  This  knob,  in  another 
form  of  this  instrument,  is  attached  to  a  spring  (Fig.  164).  This 
box  or  tympanum  is  in  connection  with  another  box,  the  recording 
tambour,  by  means  of  a  tube,  and  upon  the  elastic  membrane  of 
this  rests  a  lever.  The  first  tambour  is  so  fixed  in  place  against 
the  chest  wall  as  to  bring  the  knob  over  the  point  where  the 
cardiac  impulse  is  felt,  and  the  movement  of  the  knob  is  com- 


CIRCULATION  OF  THE  BLOOD. 


313 


municated  to  the  membrane,  sending  a  wave  of  air  through  the 
tube  and  causing  the  lever  to  move  at  every  impulse ;  the  point  of 
the  lever  makes  its  record  on  a  revolving  drum  or  kymograph, 
covered  with  smoked  paper  (Fig.  1 66).  This  may  be  varnished 
with  shellac  for  preservation.  Fig.  164  shows  a  cardiogram  taken 
in  this  way. 

The  same  instrument  in  a  modified  form  is  used  to  obtain  a 
record  of  the  endocardiac  pressure.  In  this  case  India-rubber 
bags  communicating  with  the  recording  tambours  are  introduced 
through  the  jugular  vein  into  the  cavities  of  the  right  auricle 
and  ventricle.  This  method  is  of  service  only  in  an  animal  with 
large  vessels,  such  as  the  horse. 

Movements  of  Blood  during  Systole  and  Diastole. — Before  con- 
sidering other  movements  of  the  heart  it  will  be  well  to  study  the 
course  of  the  blood  while  contraction  and  relaxation  of  the  mus- 
cular tissue  of  this  organ  are  taking  place. 

The  venous  blood,  returning  from  the  head  and  upper  extrem- 
ities by  the  superior  or  descending  vena  cava,  and  from  the  portion 
of  the  body  below  the  heart  by  the  inferior  or  ascending  vena 


FIG.  163.— Diagram  of  Marey's 
cardiograph :  A,  knob  attached  to 
flexible  membrane  tied  over  end 
of  metal  box  ;  the  knob  is  placed 
over  the  apex-beat ;  c,  folded  edge 
of  membrane;  Bis  the  tube  commu- 
nicating with  a  recording  tambour. 


FIG.  164.— Cardiogram  taken  with 
Marey's  cardiograph :  a,  auricular 
systole ;  v,  ventricular  systole ;  d, 
diastole.  The  arrow  shows  the  di- 
rection in  which  the  tracing  is  to 
be  read  (Stewart). 


cava,  flows  into  and  through  the  right  auricle,  passing  into  the 
right  ventricle  through  the  right  auriculoventricular  orifice.  The 
tricuspid  valve  at  this  time  is  open,  and  offers  no  obstacle  to  the 
passage  of  the  blood.  Blood  is  also  at  the  same  time  flowing  into 
the  left  auricle  and  ventricle  from  the  lungs.  More  blood  enters 
the  auricles  than  can  at  once  pass  out  into  the  ventricles ;  conse- 
quently some  blood  accumulates  in,  and  gradually  fills,  the  auricles, 
although  at  the  same  time  as  much  blood  is  flowing  into  the  ven- 
tricles as  the  auriculoventricular  orifices  will  permit  to  pass,  nearly 
filling  these  cavities,  and  floating  up  the  segments  of  the  mitral 
and  tricuspid  valves  until  they  are  nearly  closed.  This  is  the 
condition  at  the  end  of  the  pause.  At  this  moment  begins  the 
auricular  systole.  Near  the  ends  of  the  veins  which  discharge 


314  CIRCULATORY  SYSTEM. 

into  the  auricles — that  is,  the  venae  cavae  and  pulmonary  veins — 
are  muscular  fibers ;  these  fibers  contract,  diminishing  the  size  of 
the  orifices  of  the  veins,  thus  taking  the  place  of  valves,  and  par- 
tially preventing  a  back-flow  of  blood  into  these  vessels.  Then 
the  muscular  fibers  of  the  auricles  in  contiguity  with  these  fibers 
contract,  the  movement  spreading  to  the  adjoining  fibers  until  the 
wave  of  contraction  has  reached  the  ventricles.  This  auricular 
contraction  forces  more  blood  into  the  ventricles,  and  as  the  fibers 
relax  the  blood  enters  the  auricles  again  from  the  veins.  It  will 
thus  be  seen  that  the  interval  of  time  during  which  the  venous 
flow  is  arrested  is  the  briefest  possible.  The  principal  office  of  the 
auricles  is  to  serve  as  reservoirs  to  supply  the  ventricles;  the 
work  they  do  in  completing  the  filling  of  these  cavities  is  com- 
paratively unimportant. 

The  auricular  systole  is  followed  by  the  systole  of  the  ventri- 
cles. These  cavities  are  at  this  time  filled  with  blood,  and  the 
auriculoventricular  valves  are  nearly  closed,  the  segments  having 
been  raised  up  by  the  blood  from  the  auricles.  The  ventricles,  as 
has  been  stated,  contract  en  masse,  and  the  blood  which  they  con- 
tain is  compressed  with  great  force.  Under  the  pressure  it  tends 
to  escape  from  the  ventricles  through  all  outlets — on  the  right  side 
through  the  right  auriculoventricular  orifice  back  into  the  right 
auricle,  and  through  the  pulmonary  orifice  into  the  pulmonary 
artery ;  on  the  left  side  through  the  left  auriculoventricular  orifice 
into  the  left  auricle,  and  through  the  aortic  orifice  into  the  aorta. 
The  pressure  of  the  blood  instantly  closes  the  tricuspid  valve,  and 
thus  prevents  the  blood  from  going  back  into  the  right  auricle. 
The  same  force  closes  the  mitral  valve,  and  regurgitation  of 
blood  into  the  left  auricle  is  made  impossible.  The  pulmonary 
and  aortic  valves,  as  has  been  stated,  open  from  the  ventricles  into 
the  arteries.  At  the  beginning  of  the  ventricular  systole  these  valves 
are  closed,  but  when  systole  occurs  the  pressure  of  the  blood  forces 
them  open,  and  the  contents  of  the  ventricles,  70  c.c.  for  each,  are 
propelled  into  the  pulmonary  artery  and  the  aorta  respectively. 
Authorities  differ  as  to  the  amount  of  blood  which  is  expelled  from 
the  ventricle  at  each  pulsation,  and  which  is  termed  the  pulse 
volume  ;  some  place  it  as  low  as  50  c.c.,  and  others  as  high  as  190 
c.c.  Stewart  gives  it  as  his  opinion  that  the  average  amount  of 
blood  thrown  out  by  each  ventricle  at  each  beat  is  not  more  than 
70  c.c.  or  80  c.c.  (87  grams).  This  agrees  closely  with  Tiger- 
stedt's  calculation,  which  places  the  amount  at  69  c.c.  If  the 
average  amount  is  70  c.c.,  the  whole  blood  of  the  body  would  pass 
through  the  heart  in  about  a  minute.  In  accomplishing  this  the 
ventricles  have  to  overcome  the  pressure  which  the  blood  already 
in  the  arteries  is  exerting  on  the  other  side  of  the  valves  to  keep 
them  closed.  This  pressure  in  the  arteries  is  equal  to  a  column 
of  mercury,  approximately,  150  mm.  high,  and  in  the  pulmonary 


CIRCULATION  OF  THE  BLOOD.  315 

artery  is  one-third  as  much.  The  amount  of  work  done  by  the 
ventricles  daily  in  thus  forcing  blood  into  the  arteries  is  equal  to 
that  which  is  performed  by  an  individual  weighing  75  kilograms 
in  climbing  a  mountain  806  meters  in  height. 

As  soon  as  the  ventricles  cease  their  contraction  the  pressure 
of  the  blood  in  the  arteries  closes  the  pulmonary  and  aortic  valves, 
the  ventricles  begin  their  diastole,  and  the  pause  of  the  heart 
commences.  As  it  was  at  this  point  that  the  consideration  of  the 
changes  which  take  place  was  begun,  the  study  of  a  cardiac  cycle, 
cardiac  period,  or  heart-beat  is  now  completed.  If  the  time 
occupied  by  such  a  period  is  divided  into  one  hundred  parts,  it 
will  be  found  that  the  auricular  systole  lasts  during  nine  of  the 
parts,  the  ventricular  systole  during  thirty,  and  the  pause  during 
sixty-one ;  or,  in  other  words,  the  heart  is  at  rest  six-tenths  and 
at  work  four-tenths  of  the  time. 

Shortening  of  the  Heart. — At  the  time  of  the  systole  of  the 
heart  (ventricular  systole)  the  organ  becomes  shorter,  yet  the  apex 
does  not  change  its  place,  for  the  lengthening  of  the  aorta  which 
occurs  compensates  for  the  shortening,  so  that  while  the  apex  and 
base  approximate  the  whole  heart  is  lowered,  the  result  being  to 
keep  the  apex  in  its  original  position  with  reference  to  the  chest 
wall. 

Cardiac  Impulse. — The  situation  of  the  heart  in  the  thoracic 
cavity  is  such  that  its  apex  is  against  the  chest  wall  at  the  fifth 
intercostal  space,  the  space  between  the  fifth  and  sixth  ribs,  and 
about  3  cm.  below  and  1  cm.  within  the  left  nipple.  The  apex  of 
the  heart  is  the  extreme  point  of  the  left  ventricle.  If  the  finger 
is  placed  in  this  region  during  the  ventricular  systole,  there  will  be 
felt  a  tap  as  if  something  was  gently  striking  it.  This  tap  is 
known  as  the  apex-beat.  It  is  so  called  because  it  was  formerly 
supposed  that  during  the  systole  the  heart  was  raised  up  and  car- 
ried forward  so  as  to  cause  the  apex  to  strike  against  the  chest  wall 
and  thus  produce  the  sensation..  A  more  careful  study  of  the 
changes  which  the  heart  undergoes  during  systole  has,  however, 
demonstrated  that  the  apex  of  the  heart  is  always  in  contact  with 
the  chest  wall,  and  that  this  supposed  striking  does  not  take  place. 
Indeed,  the  tap  is  not  due  to  the  apex  at  all.  The  term  apex- 
beat  is  a  misnomer :  it  should  rather  be  called  cardiac  impulse, 
the  sensation  being  produced  by  the  anterior  surface  of  the  con- 
tracting ventricles  swelling  out  and  hardening.  The  location  at 
which  this  impulse  is  felt  most  pronouncedly  is  not  over  the  apex, 
but  higher  up.  If  a  long  needle  was  to  be  introduced  deeply 
here,  it  would  penetrate  the  left  ventricle  at  a  point  where 
the  middle  and  lower  thirds  unite.  The  cardiac  impulse  is  not 
always,  even  in  health,  detected  at  the  same  place  :  it  changes 
somewhat  with  respiration  and  also  with  changes  in  the  position 
of  the  body. 


316  CIRCULATORY  SYSTEM. 

Papillary  Muscles.— It  has  been  stated  that  during  the  ven- 
tricular systole  the  heart  shortens.  It  is  manifest  that  unless 
some  provision  was  made  this  change  in  the  shape  of  the  heart 
would  permit  of  regurgitation  of  the  blood  into  the  auricles, 
and  thus  would  result  a  damming  back  of  the  blood  in  the  venae 
cavse  and  pulmonary  veins ;  for  if  the  chordae  tendinese  were  of 
just  the  right  length  at  the  beginning  of  the  ventricular  systole 
to  keep  the  segments  of  the  mitral  and  tricuspid  valves  so  exactly 
in  place  as  not  to  permit  a  leakage,  then  when  the  ventricles 
shortened  these  cords  would  be  too  long,  and  would  permit  the 
segments  to  enter  the  cavity  of  the  auricles  and  there  separate, 
leaving  a  considerable  gap  through  which  the  blood  could  pass. 
That  this  does  not  occur  is  due  to  the  papillary  muscles.  As  the 
ventricles  shorten,  these  structures  contract  sufficiently  to  take  up 
the  slack  in  the  cords,  and  keep  them  just  long  enough  to  main- 
tain the  proper  approximation  of  the  segments  of  the  valves. 

Cardiac  Sounds. — When  the  ear  is  placed  against  the  chest 
wall  in  the  region  of  the  heart  two  sounds  are  heard  during  each 
cardiac  period.  The  first  of  these  sounds  is  heard  loudest — that 
is,  at  its  maximum  of  intensity — over  the  apex,  and  is  by  some 
writers  called  the  apex-sound.  For  the  reason  that  it  is  the  first 
sound  heard  after  the  pause  it  is  called  the  first  sound,  and  because 
it  occurs  at  the  beginning  of  the  systole  of  the  heart  (ventricular 
systole)  it  is  called  the  systolic  sound.  The  second  sound  is  heard 
loudest  over  the  base  of  the  heart,  and  is  therefore  sometimes  de- 
scribed as  the  basic  sound;  inasmuch  as  it  occurs  during  the 
diastole,  it  has  received  the  name  of  the  diastolic  sound.  More 
commonly,  however,  it  is  spoken  of  as  the  second  sound. 

Characteristics  of  the  Cardiac  Sounds. — The  first  sound,  as  com- 
pared with  the  second,  is  lower  in  pitch  and  longer  in  duration, 
and  has  been  likened  to  the  sound  of  the  word  liibb.  The  second 
sound  is  higher  in  pitch  and  shorter  in  duration  than  the  first,  and 
has  been  likened  to  the  sound  of  diip.  These  sounds  occur  suc- 
cessively, without  any  interval  between  them  ;  in  the  pause  which 
follows  no  sound  is  heard. 

Causes  of  the  Cardiac  Sounds. — The  cause  of  the  second  sound 
is  undoubtedly  the  closure  of  the  aortic  and  pulmonary  valves. 
This  has  been  demonstrated  by  hooking  back  the  segments  of  the 
valves,  when  the  sound  disappears,  to  reappear  when  the  seg- 
ments are  set  free.  The  causation  of  the  first  sound  is  not  so 
simple;  indeed,  authorities  are  not  at  one  on  this  point.  The 
closure  of  the  mitral  and  tricuspid  valves  contributes  something 
to  it,  but  the  closing  of  the  valves  is  not  the  sole  factor,  for  in  a 
heart  in  which  there  is  no  blood  the  sound  may  still  be  heard, 
although  modified,  and  in  such  a  heart  the  valves  would  not  close. 
The  contraction  of  the  muscular  tissue  of  the  heart  gives  forth  a 
sound,  as  does  indeed  the  contraction  of  other  muscles,  and  this 


CIRCULATION  OF  THE  BLOOD.  317 

is  also  an  element  in  producing  the  first  sound.  The  striking  of 
the  apex  against  the  chest-wall,  the  so-called  apex-beat,  formerly 
regarded  as  one  of  the  factors  of  the  first  sound,  can  take  no  part 
in  its  production,  because:,  as  has  been  pointed  out,  this  action  does 
not  take  place. 

Every  student  should  familiarize  himself  with  the  cardiac 
sounds,  not  simply  by  reading  about  them,  but  by  listening 
to  the  human  chest.  A  thorough  knowledge  of  their  character 
is  essential  to  a  comprehension  of  the  diseases  of  the  heart.  It  is 
important  to  remember  that  the  impulse  of  the  heart,  the  systole 
of  the  ventricles,  the  first  sound,  and  the  closure  of  the  mitral 
and  tricuspid  valves  are  synchronous,  and  that  when  the  second 
sound  is  heard  the  ventricles  are  beginning  their  diastole  and  the 
aortic  and  pulmonary  valves  have  just  closed. 

Cardiac  Innervation. — The  cause  of  the  beat  of  the  heart 
has  not  been  definitely  ascertained.  The  fact  that  it  beats  when 
removed  from  the  body  shows  that  this  action  is  dependent  upon 
some  power  within  itself.  The  length  of  time  that  a  heart  so  iso- 
lated will  continue  to  beat  varies  in  different  animals,  being  longer 
in  the  poikilothermal  than  in  the  homoiothermal ;  thus,  it  may  con- 
tinue for  days  in  the  former,  wrhile  in  the  latter  it  may  cease  after 
a  few  hours  or  even  minutes.  Landois  states  that  in  hearts  that 
have  been  excised  "  the  last  vestige  of  cardiac  action  has  been 
observed  in  the  rabbit  after  15J  hours,  in  the  mouse  after  46  J 
hours,  in  the  dog  after  96J  hours,  and  in  a  three-month s'-old 
human  embryo  after  4  hours." 

Two  theories  have  been  advanced  to  explain  the  beat  of  the 
heart:  (1)  That  it  is  due  to  stimuli  having  their  origin  in  nerve- 
ganglia  which  exist  in  the  heart ;  and  (2)  that  it  is  due  to  an  in- 
herent power  of  contraction  residing  in  the  cardiac  muscle-cells,  a 
power  independent  of  any  nervous  connection  whatsoever,  and  that 
this  is  due  to  the  action  upon  the  heart  muscle  of  chemical  sub- 
stances in  the  blood,  as  calcium,  sodium,  and  potassium  salts;  the 
first  being  apparently  essential  for  the  chemical  stimulation,  while  a 
certain  proportion  of  potassium  is  also  necessary  (Ho well).  The 
effect  of  the  sodium  chlorid  is  to  maintain  the  osmotic  equilibrium 
between  the  muscle-cells  and  the  surrounding  liquid. 

The  first  of  these  theories  is  supported  by  the  fact  that  there 
are  numerous  ganglion-cells  in  the  heart,  and  that  where  these  are 
most  abundant,  as  in  the  auricle,  there  the  power  of  contraction  is 
greater  than  in  the  part  (the  ventricle)  where  the  cells  are  fewer ; 
and,  further,  that  when  the  apex  of  the  heart — i.  e.,  the  point  of 
the  ventricle  in  which  there  are  no  cells — is  cut  away,  it  no  longer 
beats.  The  second  theory  derives  its  support  from  the  fact  that  a 
piece  of  the  apex  of  the  ventricle  of  a  tortoise,  in  which  there  are 
no  ganglion-cells,  when  suspended  in  a  moist  chamber,  will  beat 
for  hours.  The  apex  of  a  dog's  heart,  in  which  there  are  no  cells, 


318  CIRCULATORY  SYSTEM. 

will  beat  for  hours,  provided  it  is  supplied  with  defibrinated  blood 
through  its  nutrient  artery  (Porter).  This  second  theory  is  rapidly 
gaining  favor  among  physiologists. 

Cardiac  Nerves. — Whatever  may  be  the  cause  of  the  heart-beat, 
its  regulation  is  brought  about  by  the  central  nervous  system.  The 
cardiac  nerves  are  derived  from  two  sources,  the  vagus  and  the 
sympathetic,  through  the  cardiac  plexuses,  of  which  there  are  four  : 
1,  the  superficial,  situated  in  the  concavity  of  the  arch  of  the 
aorta ;  2,  the  deep,  or  great ;  3,  the  right  coronary,  and,  4,  the  left 
coronary  ;  the  last  two  being  derived  from  the  superficial  and  the 
deep.  The  impulses  which  reach  the  heart  through  the  vagus  are 
of  an  inhibitory  nature,  while  those  passing  through  the  sympa- 
thetic are  accelerating  or  augmenting  (pp.  487  and  523). 

Circulation  in  the  Arteries. — Each  time  that  the  ven- 
tricles contract  they  send  into  the  arteries  about  140  c.c.  of 
blood,  each  ventricle  expelling  70  c.c.  (p.  314).  The  arterial 
system  is  always  overdistended — that  is,  even  when  the  heart 
is  at  rest  the  amount  of  blood  in  the  arteries  is  sufficient  to  stretch 
their  walls  a  little.  When  an  additional  amount  of  blood  is  forced 
into  them  by  the  muscular  contraction  of  the  heart,  these  vessels 
are  distended  still  more,  for  the  blood  already  in  them  cannot  at 
once  flow  on  in  an  amount  equal  to  that  which  comes  from  the 
heart.  If  an  artery  at  this  time  should  be  felt  with  the  finger,  it 
would  beat  against  the  latter,  this  beat  being  called  the  pulse.  As 
soon  as  the  systole  ceases  the  elastic  coats  of  the  arteries  squeeze 
the  blood  that  is  within  them,  and  this  blood  tends  to  flow  away 
from  the  point  of  pressure  in  two  directions — back  toward  the  heart 
and  onward  toward  the  capillaries.  Its  backward  flow  at  once 
closes  the  pulmonary  and  aortic  valves,  and  in  this  direction, 
therefore,  its  progress  is  barred.  The  blood  then  can  go  only 
forward.  Before  the  onward  flow  of  the  blood  has  ceased  another 
systole  occurs,  and  again  the  ventricles  are  emptied  into  the 
arteries,  and  thus  this  action  continues  during  the  life  of  the 
individual.  If  a  cannula  is  inserted  into  the  cavity  of  the  ventri- 
cle, it  will  be  seen  that  at  each  systole  the  blood  spurts  out 
in  a  jet,  which  ceases  at  the  end  of  the  systole — that  is,  the 
flow  from  the  heart  is  intermittent.  If  the  cannula  is  inserted 
into  the  aorta,  the  blood  will  jet  out  at  each  systole  of  the  heart, 
but,  instead  of  ceasing  to  flow  during  diastole,  it  will  not 
entirely  cease,  but  will  continue  to  flow  a  little  under  the  influence 
of  the  elastic  force  of  the  aorta.  If  the  cannula  is  inserted  into 
successive  portions  of  the  arterial  system  farther  and  farther  from 
the  heart,  the  blood  will  come  out  in  jets  as  before  under  the  influ- 
ence of  the  heart's  contraction,  but  it  will  continue  to  flow  in  the 
intervals,  the  difference  between  the  jet  and  the  continuous  flow 
being  less  and  less  marked  the  greater  is  the  distance  of  the  inser- 
tion of  the  cannula  from  the  heart.  In  the  capillaries  the  flow  is 
regular  and  continuous,  unaffected  by  the  action  of  the  heart. 


EL  0  OD-PRESS  URE. 


319 


Internal  Friction. — If  the  blood  is  studied  as  it  is  flowing 
through  a  small  artery  in  the  web  of  a  frog's  foot,  it  will  be  seen 
that  in  the  center  of  the  current  it  is  flowing  much  faster  than  at 
the  sides ;  this  is  the  axial  stream,  and  in  it  will  be  observed  the 
red  corpuscles.  That  portion  of  the  current  which  is  between  the 
axial  stream  and  the  walls  of  the  vessel  moves  more  slowly, 
the  rate  diminishing  from  the  center  outward,  until  at  the  walls 
themselves  it  is  at  the  minimum.  This  outer  portion  is  known  as 
the  inert  layer.  It  should  be  stated  that  this  arrangement  of  the 
current  is  not  due  to  any  peculiarity  of  the  blood  or  of  the  vessels 
through  which  it  flows,  but  is  present  in  every  fluid  while  flowing 
through  a  tube.  Between  the  different  layers  of  fluid  there  is 
friction,  called  internal  friction.  The  smaller  the  tubes  the  greater 
the  internal  friction,  so  that  the  amount  of  friction  in  the  sub- 
divisions of  the  aorta  and  its  numerous  ramifications  is  very 
great,  and  this  friction  acts  as  an  obstacle  to  the  outflow  of  the 
blood,  constituting  peripheral  resistance. 


BLOOD-PRESSURE. 

The  systemic  circulation  of  the  blood — i.  e.,  its  flow  from  the 
left  ventricle  through  the  arteries  and  capillaries ;  and  back  by  the 
veins  to  the  right  ventricle  again — is  a  movement  from  a  point  of 
high  pressure,  the  left  ventricle,  to  one  of  low  pressure,  the  right 


FIG.  165. — Height  of  blood-pressure   (b.p.)  in  left  ventricle  (l.v.) :  a,  arteries;  c, 
capillaries  ;  r,  veins  ;  r.a.,  right  auricle ;  o  0,  line  of  no  pressure  (after  Starling). 

auricle.  This  is  shown  in  Fig.  165,  where  the  pressure  is  greatest 
at  the  left  ventricle,  gradually  diminishing  in  the  large  arteries, 
until  at  the  end  of  the  arterial  system  the  fall  is  abrupt ;  it  falls 
gradually  throughout  the  capillaries  and  veins  until  the  large  veins 
in  proximity  to  the  heart  are  reached,  where  it  is  negative  (p.  323). 
The  fact  that  the  blood  within  the  vessels  is  under  varying 
degrees  of  pressure  may  be  demonstrated  by  repeating  the  classic 
experiment  performed  by  Stephen  Hales,  an  English  Episcopal 
clergyman,  and  described  by  him  in  u  Statical  Essays,  Containing 
Hsemostaticks."  This  was  published  in  London  in  1733.  He  in- 


320 


CIRCULATORY  SYSTEM. 


FIG.  166. — Diagram  of  the  recording  mercurial  manometer  and  the  kymo- 
graph ;  the  mercury  is  indicated  in  deep  black :  M,  the  manometer,  connected  by 
the  leaden  pipe  L  with  a  glass  cannula  tied  into  the  proximal  stump  of  the  left 
common  carotid  artery  of  a  dog;  A,  the  aorta  ;  C,  the  stop-cock,  by  opening  which 
the  manometer  may  be  made  to  communicate  through  ET,  the  rubber  tube,  with  a 
pressure-bottle  of  solution  of  sodium  carbonate ;  F,  the  float  of  ivory  and  hard 
rubber;  R,  the  light  steel  rod,  kept  perpendicular  by  B,  the  steel  bearing;  P,  the 
glass  capillary  pen  charged  with  quickly  drying  ink  ;  T,  a  thread  which  is  caused, 
by  the  weight  of  a  light  ring  of  metal  suspended  from  it,  to  press  the  pen  obliquely 
and  gently  against  the  paper  with  which  is  covered  D,  the  brass  "drum"  of  the 
kymograph,  which  drum  revolves  in  the  direction  of  the  arrow.  The  supports  of 
the  manometer  and  the  body  and  clock-work  of  the  kymograph  are  omitted  for  the 
sake  of  simplicity.  The  aorta  and  its  branches  are  drawn  disproportionately  large 
for  the  sake  of  clearness  (Curtis). 

troduced  into  the  femoral  artery  of  a  horse  a  brass-pipe  whose 
bore  was  one-sixth  of  an  inch  in  diameter,  to  that,  by  means  of 


BLOOD-PRESSURE.  321 

another  brass-pipe  which  was  fitly  adapted  to  it,  "  was  attached  a 
glass  tube  of  nearly  the  same  diameter,  which  was  nine  feet  in 
length";  the  blood  rose  to  a  height  of  2.44  meters,  and  at  each  in- 
spiration of  the  animal  the  column  rose  and  at  each  expiration  it  fell ; 
besides  this  movement  due  to  respiration,  there  was  a  smaller 
rise  at  each  systole  and  a  corresponding  fall  at  each  diastole. 
This  pressure  under  which  the  blood  is  in  the  artery  which  causes 
it  to  rise  so  high  in  the  tube  is  arterial  pressure,  or  the  blood- 
pressure  in  the  arteries.  Such  an  instrument  for  measuring 
pressure  is  a  manometer.  It  is  manifest  that  a  glass  tube  2^ 
meters  in  height  is  not  a  very  convenient  instrument  to  manipu- 
late, and  besides  the  blood  soon  clots.  To  obviate  both  of  these 
difficulties  the  mercurial  manometer  was  devised,  together  with  the 
use  of  a  solution  of  sodium  carbonate ;  the  latter  preventing  the 
coagulation  of  the  blood.  Later  a  drum  or  kymograph  was  added 
to  the  apparatus,  on  which  a  record  could  be  made  for  study  and 
preservation  (Fig.  166).  The  legend  beneath  the  illustration  is 
sufficiently  descriptive  of  the  complete  apparatus.  The  curve 


P 

BL 


FIG.  167. — The  trace  of  arterial  blood -pressure  from  a  dog  anesthetized  with 
morphia  and  ether.  The  cannula  was  in  the  proximal  stump  of  the  common  carot- 
id artery.  The  curve  is  to  be  read  from  left  to  right:  P,  the  pressure-trace  written 
by  the  recording  mercurial  manometer ;  B  L,  the  base-line  or  abscissa,  representing 
the  pressure  of  the  atmosphere.  The  distance  between  the  base-line  and  the  press- 
ure-curve varies,  in  the  original  trace,  between  62  and  77  millimeters,  therefore  the 
pressure  varies  between  124  and  154  millimeters  of  mercury,  less  a  small  correction 
for  the  weight  of  the  sodium-carbonate  solution  ;  T,  the  time-trace,  made  up  of 
intervals  of  two  seconds  each,  aud  written  by  an  electro-magnetic  chronograph 
(Curtis). 

made  by  the  pen  is  shown  in  Fig.  167.  The  longer  waves  are 
due  to  respiration,  the  smaller  ones  to  the  heart-beat.  By  the 
term  mean  pressure  is  meant  the  average  pressure  throughout  the 
observation.  The  mean  arterial  pressure  in  man  is  approximately 
150  mm.,  an  increase  of  5  mm.  occurring  at  the  time  of  systole. 

The  figures  here  given  for  the  mean  aortic  pressure  may  be  too 
high ;  it  has,  of  course,  never  been  measured  in  man.  The 
following  table  (Starling)  gives  the  approximate  heights  in  differ- 
ent portions  of  the  vascular  system,  calculated  largely  from  obser- 
vations in  lower  animals  : 
21 


322 


CIRCULATORY  SYSTEM. 


Large  arteries  (e.g.,  carotid) -f  140  mm.  of  mercury. 

Medium  arteries  (e.  g.,  radial) +110 

Capillaries -f  15  to  -f  20 

Small  veins  of  arm +9 

Portal  vein -f  10 

Inferior  vena  cava -j-  3 

Large  veins  of  neck from  0  to  —  8 

The  Sphygmometer  (Fig.  168). — The  sphygmometer  is  an 
instrument  for  ascertaining  the  blood-pressure  in  the  human 
subject.  It  consists  of  a  rubber  bag,  containing  a  colored  fluid, 
connected  with  a  graduated  glass  tube,  the  top  of  which  is 
expanded  into  a  bulb  and  closed  with  a  stopcock.  The  instru- 
ment is  so  attached  to  the  body  that  the  rubber  bag  is  on  the 
artery  whose  blood-pressure .  is  to  be  ascertained.  The  bag  being 
pressed  down  upon  the  artery,  the  fluid  rises  in  the  tube,  and  the 
air  in  the  bulb,  being  compressed,  acts  as  an  elastic  spring.  The 
top  of  the  fluid  is  watched  carefully,  and  when  its  pulsation  is 
greatest,  which  is  known  as  the  maximal  pulsation,  its  height  is 
read  off  on  the  scale ;  this  is  so  graduated  as  to  correspond  to 
millimeters  of  mercury  pressure,  and  represents  the  arterial  press- 
ure. By  this  instrument  the  radial  pressure  of  an  adult  has 


FIG.  168. — Hill  and  Barnard's  sphygmometer. 

been  found  to  be  from  110  to  120  mm.  of  mercury.     The  instru- 
ment can  also  be  used  to  obtain  venous  pressure. 

Stewart  states  that  the  blood-pressure  in  the  radial  artery  of  a 
healthy  man  may  average  150  mm.  of  mercury.  In  the  anterior 
tibial  artery  of  a  boy  whose  leg  was  to  be  amputated,  it  was  found 
to  vary  from  100  mm.  to  160  mm.  according  to  the  position  of 
the  body  and  other  circumstances.  The  pressure  in  the  pulmo- 
nary artery  is  about  one-third  that  in  the  aorta.  The  mean  press- 


RATE  OF  BLOOD-FLOW  IN  THE   VESSELS. 


323 


ure  in  the  veins  is  perhaps  5  mm.  and  in  the  great  veins  near  the 
heart  negative,  so  that  a  cannula  introduced  into  this  part  of  the 
circulatory  system  would  show  a  depression  of  the  mercury  in  the 
distal  limb  of  the  manometer,  indicating  that  there  was  a  suction 
from  \vithin  the  vein  ;  this  constitutes  negative  pressure.  It  is  the 
pressure  under  which  the  blood  is  in  the  arteries  that  causes  it  to 
spurt  or  jet  when  the  vessel  is  cut,  while  the  flow  from  a  wounded 
vein  or  capillary  is  continuous. 

Pick's  spring  myograph  is  another  form  of  this  instrument, 
in  which  the  movements  of  a  hollow  spring  are  communicated 
to  a  writing  lever. 


RATE  OF  BLOOD-FLOW  IN  THE  VESSELS. 

The  caliber  of  the  blood-vessels  is  constantly  changing,  and 
the  rate  of  the  flow  of  blood  through  them  is  subject  to  great 
variations,  so  that  any  estimate  of  the  velocity  of  the  flow  can 
at  best  be  but  approximate.  There  are  two  factors  which  enter 
into  the  problem  :  (1 )  the  caliber  of  the  vessel  at  the  point  where 
the  velocity  is  to  be  ascertained,  and  (2)  the  amount  of  blood 
passing  that  point  in  a  given  time, 
for  the  velocity  is  inversely  pro- 
portional to  the  sectional  area. 

Rate  of  Flow  in  the  Arte- 
ries.— It  is  in  these  vessels  that 
the  velocity  is  the  greatest,  begin- 
ning at  the  heart  and  gradually 
diminishing  along  the  course  of 
the  arterial  system.  Its  maximum 
is  at  the  time  of  the  systole. 

The  Stromuhr.—  One  of  the  in- 
struments used  to  determine  the 
rate  of  speed  is  the  stromuhr  of 
Ludwig  (Fig.  169).  This  consists 
of  a  U-shaped  tube,  glass  above 
and  metal  below,  expanded  into 
two  bulbs,  A  and  B,  which  can 
be  filled  from  the  top.  The  lower 
extremities  of  these  tubes  are  con- 
nected with  the  ends  of  a  divided 
artery,  so  that  the  channel  between 
the  two  is  continuous  through  the 
stromuhr.  The  instrument  is  so 
constructed  that  while  in  place  the  upper  portion,  including  the 
bulbs,  can  be  so  rotated  at  c  as  to  bring  A  in  connection  with  6, 
and  B  with  CT-,  and  this  process  repeated  as  often  as  desired,  the 
flow  through  the  instrument  not.  being  interrupted.  The  tubes 
and  the  bulb  B  are  filled  with  defibrinated  blood,  which  in  A 


a 


FIG.  169. — Diagram  of  longitudi- 
nal section  of  Ludwig's  "stromuhr." 
The  arrows  mark  the  direction  of  the 
blood-stream.  For  further  descrip- 
tion see  the  text  (Curtis). 


- . 


324 


CIRCULATORY  SYSTEM. 


reaches  only  up  to  the  mark  e;  and  the  bulb  A  is  filled  with  oil. 
The  clamps  which  close  the  ends  of  the  vessel  are  now  removed, 
the  time  being  noted,  and  the  blood  from  a  expels  the  oil  in  A 
into  B.  When  A  is  filled  with  blood  to  the  point  c?,  the  time  is 
again  noted,  and  the  capacity  of  A,  and  the  caliber  of  the  vessel 
being  known,  the  velocity  of  the  flow  may  be  calculated.  A 
single  measurement  would  not  be  sufficient  to  give  results  of 
much  value ;  but  if  at  the  moment  the  blood  reaches  d  the  instru- 
ment is  rotated,  the  bulb  B  into  which  the  oil  has  been  driven  by 
the  blood  will  be  brought  into  relation  with  a,  and  will  be  filled 
with  blood  from  the  vessel,  as  A  originally  was,  the  oil  being 
forced  into  A,  and  the  blood  contained  in  that  bulb  will  be  driven 
on  into  the  vessel  6,  thus  entering  the  circulation  again.  When 
the  oil  emerging  from  the  bulb  reaches  the  mark,  the  time  is  again 
noted,  and  the  bulb  again  rotated ;  thus  the  blood  which  is  meas- 
ured is  always  the  volume  be- 
tween e  and  d  in  A.  The  time 
between  the  rotations  is  the  time 
occupied  in  filling  the  bulb,  and 
this  may  be  recorded  on  a  kymo- 
graph. 

The  Dromograph  (Fig.  170). — 
This  consists  of  a  metal  tube, 
which  is  inserted  into  a  divided 
artery ;  in  the  side  of  the  tube 
is  an  opening,  closed  by  rubber, 
through  which  a  lever  passes, 
one  end  being  inside  the  vessel, 


FIG.  170. — Chauveau's  dromograph : 


the   other    outside,   and   so   ar- 


A,  tube  connected  with  blood-vessel  f  B,  ranged  that  its  movements  are 

metal  cylinder  in  communication  with  indicated   on  a  dial.      The   num- 

A.    The  upper  end  of  B  has  a  hole  in  i  r>          j      ,•  T 

the  center,  which  is  covered  by  a  mem-  ber  of  graduations  corresponding 

brane,   ro,    through   which  a  lever,    (7,  to  a  given  Velocity   is    known  by 

-  C_ has  a  small  disk,  j>,  at  its  lower  observing   the    deflection    of  the 


end,  which  projects  into  the  lumen  of  A, 
and  is  deflected  in  the  direction  of  the 
blood -stream 
is  registered 


lever  when  it  is  inserted  into  a 
tube 


communication   by  the  tube  E  with  a      flowing  at  a  known    rate  IS  pass- 


tambour  Z>,  the  flexible  membrane  of 
which  is  connected  with  the  lever  of 
the  pendulum  C. 


ing. 


Various  observations  have 
been  made  on  lower  animals  to 
determine  the  velocity  of  the  blood-flow  in  the  arteries.  In  the 
dog's  carotid  it  is  found  to  be  from  205  mm.  to  350  mm.  per 
second ;  in  the  same  vessel  of  a  horse,  306  mm.  ;  and  in  the 
metatarsal  artery  of  the  horse,  56  mm.  When  an  artery  divides, 
the  sectional  area  of  the  branches  is  more  than  that  of  the 
original  vessel,  and  this  consequently  results  in  a  gradually  in- 
creasing sectional  area,  and  a  .corresponding  diminution  in  the 
velocity  of  the  flow,  so  that  in  the  smaller  artery  the  speed  is 


RATE  OF  BLOOD-FLOW  IN  THE   VESSELS.  325 

greatly  reduced.  The  velocity  in  the  large  arteries  may  be  con- 
sidered as  approximately  3  dcm.  a  second. 

Rate  of  Flow  in  the  Capillaries. — The  sectional  area  of 
the  capillaries  is  700  times  greater  than  that  of  the  aorta,  where 
the  velocity  is,  perhaps,  500  mm.  per  second ;  when  this  portion 
of  the  circulatory  apparatus  is  reached  the  rate  of  flow  is  greatly 
reduced,  being  in  the  dog  from  0.5  mm.  to  0.75  mm.  per  second. 

The  rate  of  flow  through  the  capillaries  of  the  retina  has  been 
ascertained  by  Vierordt  in  his  own  eye  to  be  from  0.6  mm.  to  0.9 
mm.  per  second. 

The  length  of  any  given  capillary  through  which  a  specified 
portion  of  the  blood  passes  is  only  0.5  mm.,  so  that  the  length  of 
time  such  portion  would  remain  in  the  capillary  system  would  be 
less  than  a  second,  and  yet  during  this  brief  time  important 
interchanges  take  place  between  the  blood  and  the  tissues.  It  is 
here  that  the  tissues  receive  from  the  blood  the  materials  they 
require  for  their  nutrition,  and  in  the  case  of  glands  for  their 
secretion  ;  and  it  is  likewise  here  that  the  blood  receives  from  the 
tissues  their  waste  products.  The  thin  walls  of  the  capillaries  are 
admirably  adapted  for  this  interchange.  In  fact,  it  is  within 
bounds  to  say  that  the  heart,  the  arteries,  and  the  veins  are  simply 
subsidiary  to  the  capillaries,  the  arteries  carrying  to  these  vessels 
the  blood  which  the  heart  pumps  into  them,  while  the  veins  return 
the  blood  to  the  heart. 

Rate  of  Flow  in  the  Veins. — It  is  estimated  that  the 
sectional  area  of  the  veins  is  at  least  twice  as  great  as  that  of  the 
arteries,  and  therefore  the  velocity  would  be  twice  as  great  in  the 
arteries  as  in  the  veins.  Some  estimate  the  area  of  the  veins  as 
three  times  that  of  the  arteries.  Inasmuch  as  the  sectional  area 
of  the  veins  decreases  as  the  heart  is  approached,  the  rate  of  flow 
in  these  vessels  gradually  increases. 

The  Circulation-time. — The  length  of  time  which  the 
blood  takes  to  make  the  entire  round  of  the  body  was  first  ascer- 
tained by  dividing  the  jugular  vein  and  injecting  a  solution  of 
potassium  ferrocyanid  into  the  end  nearest  the  heart ;  the  blood 
was  collected  from  the  vein  of  the  other  side  and  tested  by  adding 
a  solution  of  ferric  chlorid  to  the  serum ;  as  soon  as  the  Prussian- 
blue  reaction  appeared  it  was  demonstrated  that  the  blood  had 
completed  the  circulation  of  the  body.  These  observations  con- 
ducted on  different  animals  gave  the  following  results :  In  the 
horse,  31.5  seconds;  dog,  16.7  seconds;  cat,  6.69  seconds;  and 
goose,  10.89  seconds. 

It  was  also  found  that  this  represented  the  time  occupied  by 
27  heart-beats  in  each  animal.  If  72  times  a  minute  are  considered 
as  representing  the  average  number  of  beats  in  man,  it  will  be  seen 
that  the  blood  requires  22.5  seconds  to  complete  the  entire  circula- 
tion. 

Stewart  has  devised  a  method  for  ascertaining  the  circulation- 


326  CIRCULATORY  SYSTEM. 

time  by  injecting  into  the  vessels  methylene-blue,  the  color  of 
which  shows  through  the  blood-vessels.  By  this  means  he  has 
been  able  to  study  the  circulation-time  in  the  lungs,  kidney,  stom- 
ach, and  other  organs  of  lower  animals.  He  thinks  that  the 
pulmonary  circulation-time — i.  e.,  the  time  occupied  by  the  blood  in 
passing  through  the  pulmonary  circulation — is  not  usually  much 
less  than  12  seconds  nor  more  than  15  seconds  ;  the  circulation-time 
of  the  kidney,  spleen,  and  liver  is  relatively  long  and  much  more 
variable  than  that  of  the  lungs,  these  organs  being  easily  affected 
by  exposure  and  changes  of  temperature  (increased  by  cold, 
diminished  by  warmth),  and  that  of  the  retina  and  heart  is  the 
shortest  of  all.  The  total  circulation -time  in  man  he  thinks  is 
not  much  less  than  a  minute,  nor  more  than  a  minute  and  a  quarter. 

THE  PULSE. 

As  has  been  seen,  the  left  ventricle  expels  at  each  beat  about 
70  c.c.  of  blood,  pumping  it  into  the  elastic  arteries ;  these  being 
already  filled,  are  still  further  distended  by  this  additional  amount, 
and  the  elastic  coat  of  the  artery  recoils  upon  the  blood  within  the 
vessel,  driving  it  still  further  along.  If  a  finger  is  placed  upon 
an  artery,  this  distention  can  be  recognized,  and  constitutes  the 
pulse.  When  the  ventricle  ceases  its  systole  and  begins  its  diastole, 
although  blood  ceases  to  be  expelled  from  it,  still  the  current  in 
the  arteries  does  not  cease,  for  the  elastic  force  of  the  vessels  is 
sufficient  to  keep  up  a  continuous  movement  of  the  fluid,  which 
while  it  is  in  the  arterial  system  is  affected  by  the  pulsation  of  the 
heart,  but  which  in  the  capillary  and  venous  systems,  is  uniform  in 
rate.  If  it  was  possible  to  place  a  finger  upon  the  carotid,  another 
on  the  radial,  and  still  another  on  the  dorsal  artery  of  the  foot,  it 
would  be  found  that  the  pulse  would  first  be  felt  in  the  artery 
nearest  the  heart,  then  in  that  at  the  wrist,  and  finally  in  the  most 
distant  one.  Thus  the  pulse-wave  starting  at  the  left  ventricle  is 
felt  in  0.159  second  at  the  wrist,  and  in  0.193  second  at  the  foot. 
It  travels  at  the  rate  of  about  9  meters  per  second. 

The  number  of  pulsations  varies  in  different  conditions,  increas- 
ing in  activity  and  diminishing  during  rest ;  it  also  varies  at  dif- 
ferent ages  :  At  birth  it  is  140  to  the  minute ;  atone  year,  120; 
two  years,  110;  three  years,  90;  seven  years,  85;  puberty,  80; 
adult  age,  70 ;  old  age,  60.  These  figures  are  approximate  only. 

Any  artery  which  is  accessible  may  be  used  to  obtain  the  pulse, 
but  physicians  have  selected  the  radial  as  the  most  convenient  be- 
cause of  its  accessibility  and  also  because  it  lies  upon  an  unyield- 
ing bony  bed,  and  can  be  readily  compressed  by  the  finger  and  its 
character  studied.  The  heart  is  one  of  the  vital  organs  of  the 
body,  and  a  knowledge  as  to  how  it  is  performing  its  functions  is 
very  important  for  the  physician  to  possess.  Situated  as  it  is 
within  the  thorax,  he  cannot  examine  it  directly,  and  is  therefore 


THE  PUL8&. 


327 


compelled  to  resort  to  other  means  to  ascertain  its  condition.  One 
of  the  best  sources  of  information  is  the  pulse.  This  he  studies 
to  learn  :  (1)  The  frequency  of  the  heart-beats,  for  each  time  the 


FIG.  171. — Scheme  of  Marey's  sphygmograph :  a,  toothed  wheel  connected  with 
axle  h,  and  gearing  into  toothed  upright  6 ;  c,  ivory  pad  which  rests  over  blood- 
vessel and  is  pressed  on  it  by  moving  g,  a  screw  passing  through  the  spring  j ;  e, 
writing-lever  attached  to  axle  h,  and  moved  by  its  rotation ;  e  writes  on  d,  a  travel- 
ling surface  moved  by  clockwork  /. 

ventricle  contracts  there  is  a  corresponding  beat  of  the  pulse ;  (2) 
the  force  with  which  the  heart  is  acting,  for  the  strength  of  the 
pulse  is  an  indication  of  that  of  the  heart ;  (3)  its  regularity;  and 


FIG.  172. — Sphygmogram  from  a  normal  human  radial  pulse  beating  from  58  to  60 
times  a  minute.     To  be  read  from  left  to  right  (Burdon-Sanderson). 

(4)  its  tension — i.  e.,  whether  it  is  compressible  or  not,  whether  a 
slight  pressure  will  obliterate  it,  or  whether  it  requires  a  greater 
amount  of  pressure.  Low  tension  implies  low  arterial  pressure, 
and  high  pressure  denotes  high  blood-pressure. 


FIG.  173. — Pulse-tracings :  1,  primary  elevation  ;  2,  predicrotic  or  first  tidal  wave ; 
3,  dicrotic  wave.  The  depression  between  2  and  3  is  the  dicrotic  or  aortic  notch  ;  3 
is  better  marked  in  B  than  in  A.  C,  dicrotic  pulse  with  low  arterial  pressure.  D, 
pulse  with  high  arterial  pressure-summit  of  primary  elevation  in  the  form  of  an 
ascending  plateau.  E,  systolic  anacrotic  pulse ;  the  secondary  wavelet  a  occurs 
during  the  upstroke  corresponding  to  the  ventricular  systole.  F,  presystolic  ana- 
crotic pulse;  a  occurs  just  before  the  systole  of  the  ventricle.  In  this  rarer  form 
of  anacrotism  a  may  sometimes  be  due  to  the  auricular  systole  when  the  aortic 
valves  are  incompetent  (Stewart). 

The  Sphygmograph  (Fig.  171). — This  instrument  makes 
a  record,  sphygmogram  or  pulse-trace,  of  the  pressure  in  the 


328 


CIRCULATORY  SYSTEM. 


arteries.  It  is  attached  to  the  wrist,  and  the  point  of  the  lever 
makes  a  sphygrnogram  upon  the  card  previously  smoked.  It 
is  an  instrument  which  needs  great  care  in  its  use  in  order  to 
make  its  records  of  practical  value.  Fig.  172  shows  a  sphygmo- 
gram  of  the  radial  pulse.  It  represents  five  complete  pulsa- 
tions of  the  artery  and  the  beginning  of  a  sixth.  The  upstroke 
is  caused  by  the  expansion  of  the  artery  due  to  the  arrival  of  the 
pulse-wave,  while  the  downstroke  is  due  to  the  retraction  of  the 
vessel.  The  upstroke,  the  primary  or  percussion-wave,  is  abrupt, 
because  the  systole  of  the  left  ventricle  is  abrupt,  but  the  down- 


FIG.  174.— Plethysmograph  for  arm:  p,  float  attached  by  A  to  a  lever  which 
records  variations  of  level  of  the  water  in  B,  and  therefore  variations  in  the  vol- 
ume of  the  arm  in  the  glass  vessel  c.  Or  the  plethysmograph  may  be  connected 
to  a  recording  tambour.  The  tubulure  at  the  upper  part  of  C  is  closed  when  the 
tracing  is  being  taken  (Stewart). 

stroke  is  gradual,  because  of  the  fact  that  the  return  of  the 
artery  to  its  former  condition  is  gradual  by  virtue  of  its  elas- 
ticity. The  downstroke  is  seen  to  be  made  up  of  a  number 
of  waves:  First,  the  predicrotic  or  tidal  wave;  second,  the 
dicrotic  wave;  and  third,  the  post-dicrotic  wave.  These  sec- 


FIG.  175. — Plethysmograph  tracing  from  arm.  The  tracing  was  taken  by  means 
of  a  tambour  connected  with  the  plethysmograph ;  the  dicrotic  wave  is  distinctly 
marked  (Stewart). 

ondary  waves  of  the  downstroke  are  termed  katacrotic.  There  is 
sometimes  a  secondary  wave  in  the  upstroke,  called  anacrotic. 
The  predicrotic  and  post-dicrotic  waves  are  supposed  to  be  due 


CIRCULATION  IN  THE  VEINS.  329 

to  the  elastic  tension  of  the  arteries,  and  are  therefore  more 
marked  when  this  is  at  its  highest.  They  are  also  caused  to 
some  extent  by  oscillation  of  the  sphygmograph.  Their  causes 
are  not  thoroughly  understood. 

The  dicrotic  wave  is,  on  the  other  hand,  a  very  constant  and 
valuable  feature  of  the  sphygmogram.  It  is  probably  caused  by 
a  second  wave,  which  is  produced  by  the  closure  of  the  aortic 
valve,  although  on  this  point  opinions  are  at  variance.  The 
arteries  are  already  filled  when  the  left  ventricle  throws  in  its 
contents,  causing  the  expansion  of  the  aorta  and  putting  its  elastic 
coat  upon  the  stretch ;  when  the  systole  is  at  an  end  the  elastic 
recoil  upon  the  blood  drives  this  fluid  both  forward  and  backward  ; 
the  backward  flow  closes  the  aortic  valve,  and,  being  suddenly 
brought  to  a  standstill,  a  wave  of  blood  is  produced  which  is 
propagated  along  the  arterial  system  closely  following  the  pri- 
mary wave  and  causing,  the  dicrotic  wave.  This  is  sometimes  so 
marked  that  it  can  be  felt  by  the  finger,  constituting  the  dicrotic 
pulse;  thus  each  pulsation  of  the  heart  produces  2  pulse-beats. 
The  sphygmograph  shows  this  condition  much  better  than  the 
finger. 

The  Plethysmograph  (Fig.  174). — This  is  an  instrument 
for  recording  the  volume-pulse — i.  e.y  the  increase  in  the  volume  of 
an  artery  caused  by  the  pulse-wave.  It  consists  of  a  chamber  into 
which  the  organ  to  be  experimented  upon  is  inserted  and  filled 
with  fluid,  the  opening  being  closed  with  a  rubber  baud.  At  the 
other  end  is  a  rubber  tube  communicating  with  a  vessel,  in  which 
is  also  fluid,  and  on  its  surface  a  float  with  a  writing-point  attached, 
which  is  so  arranged  as  to  record  on  a  drum.  If  the  arm  is 
placed  in  the  chamber  in  the  manner  illustrated,  at  every  contrac- 
tion of  the  ventricle  the  volume  of  blood  in  the  arteries  will  be 
increased,  and  a  movement  be  set  up  in  the  fluid  which  will  cause 
the  float  to  rise ;  when  the  diastole  occurs  the  float  will  sink. 
The  record  made  is  called  a  plethysmogram  (Fig.  175). 

CIRCULATION  IN  THE  VEINS. 

The  forces  which  propel  the  blood  through  the  arteries  and 
capillaries — i.  e.,  the  contractile  force  of  the  ventricles  and  the 
elastic  force  of  the  arteries,  collectively  called  the  vis  a  tergo — are 
sufficient  to  carry  the  blood  back  to  the  heart  through  the  veins  ; 
for,  as  has  been  stated,  the  pressure  in  the  aorta  is  equal  to  a 
column  of  mercury  200  mm.  in  height,  while  in  the  veins  it  is  at 
most  only  5  mm.,  and  sometimes  actually  negative,  so  that  there 
is  a  difference  in  pressure  of  195  mm.  of  mercury.  This  visa  tergo 
is,  however,  aided  by  two  other  forces  :  (1)  compression  of  the 
veins  and  (2)  aspiration  of  the  thorax. 

Compression  of  the  Veins. — It  will  be  remembered  that 
in  the  veins  there  are,  at  different  points  along  their  course,  valves 


330  LYMPHATIC  SYSTEM. 

which  are  so  arranged  as  to  permit  the  blood  to  flow  in  but  one 
direction — that  is,  toward  the  heart.  Many  of  these  veins  are  so 
situated  with  reference  to  muscles  that  when  the  muscles  contract 
the  contiguous  veins  are  compressed.  This  compression  forces  the 
contained  blood  away  from  the  points  of  pressure,  and  as  the 
closure  of  the  valves  prevents  the  blood  from  flowing  backward, 
it  must  go  forward. 

Aspiration  of  the  Thorax. — At  each  inspiration  the  cavity 
of  the  chest  is  enlarged  and  the  pressure  on  its  contents  is  dimin- 
ished. One  of  the  results  of  this  inspiration  is  the  inflowing  of 
air.  Another  result  is  the  inflowing  of  blood  into  the  venae  cavse 
and  right  auricle,  for  while  the  intrathoracic  pressure  is  dimin- 
ished, that  upon  the  blood-vessels  outside  remains  the  same.  A 
similar  tendency  exists  for  the  blood  in  the  aorta  to  flow  back  into 
the  left  ventricle,  but  this  is  prevented  by  the  aortic  valve.  This 
subject  will  be  again  discussed  in  connection  with  respiration. 

Force  of  Gravity. — The  force  of  gravity  assists  in  the 
return  of  the  blood  to  the  heart  from  the  upper  portions  of  the 
body,  but  retards  its  return  from  the  lower  portions,  so  that  as  a 
factor  in  aiding  the  circulation  as  a  whole  it  may  be  ignored.  This 
force  may,  however,  be  utilized  whenever  for  any  reason  there  is 
congestion  in  a  part — as,  for  instance,  in  a  foot  the  seat  of  inflam- 
mation. In  such  a  case  the  elevation  of  the  lower  extremity 
facilitates  the  flow  of  blood  in  the  veins  and  proves  beneficial. 
Also,  when  by  reason  of  an  imperfect  performance  of  its  function 
the  heart  fails  to  send  enough  blood  to  the  brain,  and  fainting 
occurs,  relief  will  come  more  promptly  if  the  patient  is  at  once 
placed  on  the  back,  with  the  head  lower  than  the  heart,  thus 
assisting  that  organ  in  sending  blood  to  the  anemic  brain. 

LYMPHATIC  SYSTEM. 

The  lymphatic  system  is  composed  of  lymphatic  vessels,  lymphatic 
glands,  and  the  cavities  of  the  serous  membranes. 

I/ymphatic  Vessels. — The  larger  lymphatic  vessels  struct- 
urally are  like  the  veins,  being  composed  of  three  coats,  the 
middle  coat  containing  both  muscular  and  elastic  fibers.  Unlike 
the  veins,  however,  muscular  fibers  are  found  in  the  external  coat. 
The  smaller  vessels  have  only  a  connective-tissue  coat  lined  with 
endothelium.  In  the  lymphatic  vessels,  as  in  the  veins,  are  valves 
opening  toward  the  heart,  but  they  are  nearer  together  than  are 
those  of  the  venous  system.  The  origin  of  these  vessels  in  the 
tissues,  as  a  rule,  is  by  plexuses  or  by  stomata,  as  in  serous  mem- 
branes ;  by  blind  extremities,  as  in  the  lacteals ;  or  by  lacunar 
interstices,  as  in  some  viscera  and  glands.  They  ultimately  dis- 
charge into  the  venous  system — on  the  right  side  through  the 
right  lymphatic  duct,  and  on  the  left  side  through  the  thoracic 
duct. 


LYMPHATIC  VESSELS. 


331 


Right  Lymphatic  Duct. — The  lymphatic  vessels  of  the  right 
side  of  the  head,  neck,  and  thorax,  and  of  the  right  arm, 
right  lung,  right  side  of  the  heart,  and  a  portion  of  the  convex 
surface  of  the  liver,  discharge  into  the  right  lymphatic  duct,  which 
in  turn  discharges  into  the  right  subclavian  vein,  at  its  junction 
with  the  right  internal  jugular  vein.  It  is  about  1.25  cm.  in 
length  and  about  2  mm.  in  diameter.  At  its  junction  with  the 
venous  system  there  are  two  semilunar  valves,  to  prevent  regurgi- 
tation  of  the  blood. 

Thoracic  Duct. — All  the  lymphatics  not  connected  with  the 
right  lymphatic  duct  discharge  into  the  thoracic  duct.  This  vessel 


Scalenusanticus. 


Brachial  plexus. 


Superficial  cer- 
vical vein. 


Axillary  lym- 
phatic trunk. 


Esophagus 


Vertebral  vein. 
FIG.  176.— Topography  of  the  thoracic  duct  (Zuckerkandl). 

begins  at  the  receptaculum  chyli  or  reservoir  or  cistern  of  Pecquet, 
which  is  situated  upon  the  body  of  the  second  lumbar  vertebra, 
and  terminates  in  the  left  subclavian  vein,  where  it  joins  the  left 
internal  jugular  vein.  The  duct  is  from  38  cm.  to  45  cm.  long, 
about  the  size  of  a  goose-quill  at  commencement  and  termination, 
and  somewhat  smaller  in  the  middle  of  its  course. 

Structure  of  the  Thoracic  Duct  (Figs.  176,  177).— The  thoracic 
duct  is  composed  of  three  coats  :  an  internal,  composed  of  a  single 


332 


LYMPHATIC  SYSTEM. 


layer  of  endothelium,  a  subendothelial  layer,  and  an  elastic  fibrous 
layer ;  a  middle,  consisting  of  connective,  elastic,  and  muscular 
tissues;  and  an  external,  also  containing  connective,  elastic,  and 
muscular  tissues. 

I/ymphatic  Glands  (Fig.  178). — The  lymphatic  glands  are 
bodies  of  a  pale  reddish  color,  and  are  oval  in  shape.  Their 
diameter  is  from  2  mm.  to  20  mm.  Lymphatic  vessels  run  into 
the  glands — the  afferent;  and  out  of  them — the  efferent;  and 
through  them  pass  the  lymph  and  the  chyle.  They  consist  of  a 
capsule  of  connective  tissue,  from  which  are  given  off  trabeculce 


Longus  colli  muscle. 


Thyroid 
gland. 


Thyrocervi- 
cal  artery. 


-  Costocervi- 
cal  artery. 


Esophagus 


Trachea. — 


Axillary 
lymphatic 
trunk. 


Internal  jugular  vein. 
FIG.  177.— Topography  of  the  thoracic  duct  (Zuckerkandl). 

made  up  of  connective  tissue  with  some  muscular  fiber-cells ; 
these  pass  into  the  gland  toward  the  center  or  medullary  portion 
(M)  for  about  one-fourth  of  the  distance,  dividing  this  outer  or 
cortical  portion  into  alveoli  (C).  The  trabeculse  then  divide  and 
subdivide,  forming  a  network  in  the  medullary  portion,  the  spaces 
between  these  smaller  trabeculae  being  also  alveoli.  The  alveoli 
contain  gland-pulp  or  lymphoid  tissue,  which  consists  of  retiform 
tissue  with  lymph-corpuscles,  with  numerous  capillary  blood- 
vessels. Between  the  gland-pulp  and  the  trabeculse  in  the  cortical 
portion  there  is  a  space  (l.s),  which  is  termed  a  lymph-path  or  lymph- 


CAVITIES  OF  SEROUS  MEMBRANES. 


333 


sinm.  The  afferent  vessel  a.l.  loses  all  its  coats,  save  the  endo- 
thelial,  as  it  enters  the  gland,  and  this  is  continuous  with  that 
lining  the  lymph-sinus ;  the  same  is  true  of  the  efferent  vessel, 
which  emerges  at  the  hilum.  The  structure  of  the  lymphatic 
gland  is  such  that  the  lymph  in  its  flow  passes  through  the  pulp 
and  takes  up  lymphocytes.  It  may  also  deposit  any  poisonous 
matter  which  it  has  absorbed,  and  thus  prevent  its  entrance  into 
the  blood.  The  arteries  supplying  blood  to  the  gland  enter  at  the 
hilum,  and  the  veins  emerge  at  the  same  point. 


FIG.  178.— Diagram  of  a  lymphatic  gland,  showing  afferent  (a.l.)  and  efferent 
(e.l.)  lymphatic  vessels ;  cortical  substance  ((7)*;  medullary  substance  (M) ;  fibrous 
coat  (c),  sending  trabeculse  (tr)  into  the  substance  of  the  gland,  where  they  branch, 
and  in  the  medullary  part  form  a  reticulum ;  the  trabeculse  are  surrounded  by  the 
lymph-path  or  sinus  (Is),  which  separates  them  from  the  adenoid  tissue  (Ik) 
(Sharpey). 

Cavities  of  Serous  Membanes. — The  serous  membranes 
are  closed  lymph-sacs,  made  up  of  connective  tissue  lined  inter- 
nally with  pavement-epithelial  cells,  termed  endothelium.  Be- 
tween some  of  these  cells  are  openings — stomata — which  are 
surrounded  by  small  protoplasmic  cells.  They  are  very  distinct 
in  the  peritoneal  covering  of  the  rabbit's  diaphragm.  The 
stomata  are  openings  into  the  lymphatic  vessels  through  which 
lymph  is  pumped  by  the  contraction  and  dilatation  of  the  serous 
cavities,  brought  about  by  respiration  and  circulation. 

The   serous   membranes  are:  (1)  peritoneum ;  (2)  pleura;  (3) 


334  DUCTLESS  GLANDS. 

pericardium,  which  on  account  of  its  fibrous  layer  is  termed  fibro- 
serous  ;  (4)  tunica  vaginalis  testis. 

CIRCULATING    LYMPH. 

The  lymph  and  its  source  having  been  discussed  (p.  302),  need 
not  again  be  referred  to.  It  is  taken  up  by  the  lymphatic  capil- 
laries in  the  tissues  by  endosmosis,  and,  as  it  accumulates  there, 
gradually  fills  the  larger  vessels,  and,  as  it  is  readily  discharged 
into  the  venous  system,  there  is  set  up  a  current  which  constitutes 
the  lymphatic  circulation.  It  is  to  be  noted,  however,  that  there 
is  no  true  circulation,  as  in  the  case  of  the  blood.  The  blood  goes 
out  from  the  heart  and  returns  again,  completing  a  circuit,  but 
here  the  flow  is  always  in  one  direction,  toward  the  heart. 

Additional  aids  to  the  endosmotic  force  in  producing  the  move- 
ment of  the  lymph  are  the  contractions  of  the  muscles  of  the  body, 
by  which,  as  in  the  veins,  the  lymphatics  are  compressed,  and  the 
lymph,  being  prevented  by  the  valves  from  flowing  back,  is  pro- 
pelled toward  the  heart.  The  pressure  exerted  by  the  walls  of 
the  aorta  in  its  pulsations  compresses  the  thoracic  duct  in  a  similar 
manner,  and,  as  this  possesses  valves,  the  onflow  of  the  lymph 
and  chyle  is  favored.  The  force  of  aspiration  of  the  thorax  is 


FIG.  179.— Endothelial  cells  from  small  artery  of  the  mesentery  of  a  rabbit :  stained 
with  silver  nitrate  and  hematoxyliu  (Huber). 

also  a  factor  in  the  movement  of  the  lymph,  acting  as  was  stated 
in  the  case  of  the  venous  blood.  It  has  been  estimated  that  the 
amount  of  lymph  absorbed  daily  in  a  human  adult  is  about  2000 
grams,  and  of  lymph  and  chyle  together  3000  grams. 

DUCTLESS  GLANDS* 

This  term  includes  the  spleen,  the  thyroid  and  parathyroids, 
the  thymus,  the  suprarenal  capsules,  the  pineal  gland,  the  pituitary 
body,  the  carotid  and  coccygeal  glands,  and  the  lymphatic  glands, 
the  last  of  which  we  have  already  considered.  They  have  re- 
ceived this  name  because  they  lack  secretory  ducts.  For  -the 
reason  that  they  are  believed  by  some  to  have  important  relations 
to  the  blood  they  are  sometimes  described  as  blood-glands  or  vas- 
cular glands. 

We   have  seen   that  although  the  lymphatic  glands  have  no 


THE  SPLEEN. 


335 


proper  duct,  still  there  are  added  to  the  lymph  during  its  passa 
through  the  glands  the  lymphocytes,  which  are  a  product  of  the 
gland,  and  it  is  now  held  that  in  a  similar  manner  while  the  blood 
is  passing  through  the  ductless  glands  their  product  is  added  to  it 
This  product  is  regarded  as  an  internal  secretion. 


THE  SPLEEN, 


The  spleen  is  the  largest  of  the  ductless  glands,  and  its  func- 
tion is,  doubtless,  the  most  important.     Its  location  is  in  the  left 


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FIG.  180.— Part  of  a  section  through  the  human  spleen  :  X  75  (sublimate  fixation). 
At  a  is  an  oblong  Malpighian  body  with  a  blood-vessel  (Bohm  and  Davidoff). 

hypochondrium  between  the  stomach  and  diaphragm.  Instances 
are  on  record  in  which  the  organ  was  absent,  while  sometimes  it 
is  so  divided  as  to  present  the  appearance  of  a  considerable  number 
of  small  spleens. 

Weight.— The  weight  of  the  spleen  varies  at  different  periods 
of  life,  being  at  birth  to  the  entire  body  as  1  is  to  350 ;  in  adult 
life,  as  1  to  320  and  400  ;  and  in  old  age,  as  1  to  700,  while  in 


336 


DUCTLESS  GLANDS. 


certain  diseased  conditions,  such  as  ague,  syphilis,  or  heart  disease, 
it  may  be  enormously  increased,  in  some  cases  as  much  as  1  to  7, 
or  9  kilograms,  the  average  normal  weight  being  about  176  grams 
in  the  cadaver,  or  about  225  grams  during  life,  on  account  of  the 
contained  blood.  Its  color  is  dark  red.  The  size  of  the  spleen  is 
greatest  during  digestion,  and  least  during  starvation. 

Chemical  Composition. — The  spleen  consists  of  about  75 
per  cent,  water  and  25  per  cent,  solids,  of  which  only  about  1 
per  cent,  is  inorganic,  a  part  being  iron.  The  organic  ingredients 
are  proteids,  among  them  being  a  cell-globulin  and  a  nucleo- 
proteid ;  whether  peptones  exist  or  not  is  still  undecided ;  hemo- 
globin, xanthin,  uric  acid,  glycogen,  cholesterin,  lecithin,  and  the 
fatty  acids,  formic,  acetic,  and  butyric.  The  reaction  of  the  gland 


Intr^lobular  trabec — 
ula. 


Artery  to  one  of  the— 
ten  compartments. 


Intralobular  artery 


Interlobular  trabec-  -  - 
ula. 


Intralobular  trabec-  * — 
ula. 


Man  cor-  • 

puscle. 


Capsule. 

•  Intralobular  venous 
i    spaces. 

"Intralobular  vein. 

| 

""Ampulla  of  Thoma. 

I 

-  -  Spleen  pulp  cord. 


-L  -----  Interlobular  vein. 


Intralobular  vein. 


FIG.  181.— Diagram  of  lobule  of  the  spleen  (Mall,  Johns  Hopkins  Hospital  Bulletin, 

Sept.,  Oct.,  1898). 

is  alkaline  during  life,  becoming  acid  after  death,  due  to  the  forma- 
tion of  sarcolactic  acid. 

Structure. — The  outer  covering  is  peritoneal,  and  is  closely 
adherent  to  the  nbro-elastic  coat  or  tunica  propria,  the  two  form- 
ing practically  one.  From  it  are  given  off  trabeculce,  which  form 
the  framework  of  the  organ,  in  the  interspaces  of  which,  areolce, 
is  the  splenic  pulp,  a  soft  material  with  a  reddish-brown  color, 
within  which  are  whitish  bodies,  Malpighian  corpuscles  (Figs.  180, 
181),  composed  of  lymphoid  tissue,  and  having  a  diameter  of  from 
%  mm.  to  1  mm.  The  spleen-pulp,  when  examined  under  the 
microscope,  is  seen  to  be  made  up  of  connective-tissue  corpuscles, 
the  sustentacular  cells,  from  which  are  given  off  processes  that 
form  by  their  union  a  network  in  the  areolse  of  which  is  blood, 
characterized  by  a  large  number  of  white  corpuscles.  The 


THE  SPLEEN.  337 

sustentacular  cells  possess  ameboid  movement,  and  in  some  of 
them  reddish  granules,  resembling  hematin,  are  seen  ;  also  red  cor- 
puscles in  various  stages  of  disintegration.  In  young  spleens 
Klein  has  seen  these  cells  each  with  a  large  nucleus  from  which 
project  bud-like  processes,  and  it  has  been  suggested  that  these 
are  possibly  white  corpuscles  in  the  process  of  formation. 

The  splenic  artery  enters  the  spleen  at  the  hilum,  after 
having  divided  into  a  number  of  branches  (Fig.  181)  and  being 
covered  by  sheaths  from  the  fibro-elastic  coat.  These  arteries 
divide  and  subdivide  and  finally  end  in  the  pulp  in  small  arterioles, 
their  external  coat  gradually  changing  from  connective  tissue  to 
lyrnphoid  tissue  in  which  enlargements  occur  the  Malpighian 
corpuscles.  These  consist  of  a  delicate  reticulum  enclosing  lymph- 
corpuscles.  The  cells  which  make  up  the  reticulum  possess  ame- 
boid movement. 

The  arterioles  end  in  capillaries,  which  later  cease  to  be  distinct 
vessels,  the  cells  making  up  their  walls  becoming  branched  and 
the  branches  uniting  with  the  processes  of  the  sustentacular  cells. 
The  blood  which  reaches  the  pulp  through  these  vessels  is  by  this 
means  brought  into  direct  relation  with  it.  It  is  again  collected 
into  vessels  which  ultimately  become  veins  that  emerge  from  the 
hilum  as  the  splenic  vein. 

Innervation  of  the  Spleen — The  nerves  which  are  dis- 
tributed to  the  spleen  are  derived  from  the  celiac  plexus  and  right 
vagus. 

Functions. — The  spleen  has  been  frequently  removed  from 
lower  animals  and  from  man.  In  the  human  being  this  operation, 
splenectomy,  is  performed  for  wounds  of  the  organ,  "  wandering 
spleen  "  and  enlargement  due  to  malaria,  and  that  accompanied 
with  anemia.  Splenectomy,  for  enlargement  associated  with  leuke- 
mia, is  accompanied  with  so  much  hemorrhage  that  it  is,  by  excel- 
lent authority,  regarded  as  unjustifiable. 

In  the  chapter  on  "  Surgery  of  the  Lymphatic  System,"  by 
Prof.  Warren  in  the  International  Text-Book  of  Surgery,  the  author 
says  that  the  results  of  the  many  operations  already  reported  show 
that  the  spleen  is  not  an  organ  in  any  way  essential  to  healthy 
existence.  A  diminution  in  hemoglobin  and  in  the  number  of  red 
corpuscles  is  a  constant  sequel  to  splenectomy  in  animals  as  in 
man.  This  diminution  reaches  its  height  two  to  three  weeks  after 
the  operation,  and  then  gradually  disappears.  There  is  also  a 
temporary  leukocytosis,  including  the  polynuclear  form,  the  lym- 
phocytes, and  the  eosinophiles.  In  some  instances  the  lymph- 
glands  and  the  thyroid  are  enlarged,  and  an  increased  vascularity 
of  the  bone-marrow  occurs  in  animals. 

One  of  the  most  striking  phenomena  presented  by  the  spleen  is 
the  change  in  size  which  occurs  during  digestion.  This  begins  after 
a  meal  has  been  taken,  and  continues  for  about  five  hours,  when  the 
maximum  is  reached,  after  which  its  decrease  begins.  This  has 

22 


338  DUCTLESS  GLANDS. 

been  supposed  to  indicate  that  the  spleen  serves  as  a  reservoir  for 
the  blood  which  is  needed  during  the  time  of  digestion,  and 
especially  for  that  taking  place  in  the  stomach.  The  enlargement 
is  caused  by  relaxation  of  its  muscular  tissue  and  a  dilatation  of 
the  blood-vessels. 

A  peculiar  movement  of  contraction  and  expansion  has  been 
found  by  Roy  to  occur  in  this  organ  at  intervals  of  about  a 
minute.  This  he  demonstrated  by  the  use  of  an  oneometer  (Fig. 
182).  The  principle  on  which  this  is  constructed  is  the  same  as 
that  of  the  plethysmograph  (p.  329).  It  is  a  metal  box  made  up 
of  two  halves,  fitted  together  in  such  manner  that  they  can  be 
tightly  closed,  openings  being  left  for  the  vessels  of  the  organ 
which  is  enclosed,  be  it  spleen  or  kidney.  To  each  half  is  attached 
a  membrane  between  which  and  the  metal  is  a  space  filled  with 
oil.  Any  increase  in  the  size  of  the  contained  organ  is  accom- 
panied by  an  expulsion  of  the  oil,  which  returns  when  the  organ 
becomes  smaller.  These  changes  are  recorded  by  the  oncograph. 

While  the  functions  of  the  spleen  have  not  as  yet  been  satis- 
factorily determined,  still  they  are  doubtless  comprehended  in  the 
various  theories  which  have  from  time  to  time  been  formulated. 


FIG.  182.— Roy's  oncometer  for  spleen  :  A,  open  ;  B,  closed. 

(1)  It  is  a  producer  of  white  blood-corpuscles.     As  to  this  func- 
tion there  is  great  unanimity  of  opinion.     The  blood  emerging  by 
the   splenic   vein  contains  more  of  these  cells  than   that  which 
enters  the  gland,  and  this  number  is  greatly  increased  in  leuko- 
cythemia  or  leukemia,  in  which  the  spleen  and  the  Malpighian  cor- 
puscles especially  are  hypertrophied.     This  disease  may  also  be 
due   to   affections    of    other   organs,    as    the    bone-marrow   and 
lymphatics. 

(2)  It  destroys  red  blood-corpuscles.     This  theory  is  based  upon 
the  fact  that  red  blood-cells  are  found  in   the  pulp   in   different 


THE  THYROID  AND  PARATHYROID.  339 

degrees  of  disintegration,  and  this  is  supposed  to  be  brought  about 
by  the  ameboid  cells  hitherto  described  (p.  336).  It  is  stated  that 
in  the  cells  of  the  spleen  hemoglobin  is  found  in  different  degrees 
of  transformation  into  other  pigments,  and  a  considerable  amount 
of  iron  is  also  found  in  the  splenic  tissue.  It  is  rather  remarkable 
that  if  hemoglobin  is  set  free  or  changed  into  bile-pigment,  one  or 
the  other  of  these  substances  is  not  found  in  the  blood  of  the 
splenic  vein,  and  yet  this  is  the  fact. 

(3)  It  is  a  producer  of  red  blood-cot*puscles.     The  formation  of 
red  blood -corpuscles  does,  doubtless,  take  place  during  fetal  life 
and  for  a  short  time  after  birth  in  man,  but  there  is  no  evidence 
that  this  function  exists  in   the  human  adult,  though  it  does  in 
some   animals,  as   the   rabbit.      Laudenbach  found   that  in  this 
animal  after  an  extensive  hemorrhage  nucleated  erythroblasts  or 
hematoblasts  are  found  in  the  splenic  pulp  and  in  the  blood  of  the 
splenic  vein,  arid  that  if  the  spleen  is  removed  the  number  of  red 
corpuscles  is  diminished,  as  is  also  the  hemoglobin.     In  an  animal 
whose  spleen  has  been  removed  the  return  of  the  red  corpuscles  to- 
their  normal  number  is  much  delayed. 

(4)  It  is  a  producer  of  uric  acid.     From  the  fact  that  uric  acid, 
as  also  xanthin,  has  been  found  in  the  spleen,  it  has  been  inferred 
that  this  is  one  of  its  functions.     The  same  is  true  of  lymphoid 
tissue  generally,  so  that  this  function  cannot  be  considered  as  one 
of  the  characteristic  functions  of  the  spleen. 

(5)  It  is  an  enzyme  producer.     Some  experimenters  have  found 
that  an  enzyme  is  produced  by  the  spleen  which  when  carried  by 
the  blood  to  the  pancreas  converts  the  trypsinogen  into  trypsin. 
This  theory  lacks  confirmation. 

Schafer  sums  up  his  views  on  the  functions  of  this  organ  in 
the  following  language :  "  Whatever  may  be  the  nature  of  its 
functions  in  relation  to  the  blood,  it  is  certain  that  the  organ  is  in 
no  way  essential  to  the  normal  nutrition  of  the  body.  It  is,  on 
the  other  hand,  not  at  all  improbable  that  the  main  function  of  the 
spleen  is  to  serve  a  mechanical  purpose,  answering  as  a  reservoir 
at  certain  periods  of  digestion  for  the  blood  which  has  to  pass 
through  the  portal  system  ;  and  the  fact  that,  as  was  first  shown 
by  Roy,  the  spleen  normally  exhibits  regular  rhythmic  contrac- 
tions and  dilatations,  seems  to  point  to  its  exercising  an  influence 
in  assisting  the  flow  of  blood  through  the  portal  vein,  and  thus 
through  the  liver." 

THE  THYROID  AND  PARATHYROID. 

The  thyroid  gland  is  also  called  the  thyroid  body  ;  it  is  situated 
in  front  of  the  trachea  or  windpipe,  and  consists  of  the  lobes 
united  by  an  isthmus.  It  weighs  from  30  to  60  grams,  and  is 
larger  in  females  than  males,  and  is  said  to  be  larger  during  men- 
struation. 


340  DUCTLESS  GLANDS. 

Chemical  Composition. — An  analysis  of  an  adult  thyroid 
gives  a  percentage  of  82.24  of  water,  17.66  of  organic  and  0.1 
of  inorganic  constituents ;  in  that  of  an  infant  the  figures  were, 
77.21,  22.35,  and  0.44  respectively.  Like  the  spleen,  it  is  alkaline 
during  life  and  acid  after  death,  the  acidity  being  due  to  the  same 
cause — the  formation  of  sarcolactic  acid.  Fatty  acids,  xanthin, 
hypoxanthin,  and  other  extractives  have  also  been  obtained 
from  it. 

The  constituents  which  possess  the  greatest  importance  are 
those  of  a  proteid  nature,  for  upon  them  it  is  believed  depend 
some  of  the  remarkable  powers  with  which  this  gland  is  endowed. 
Among  these  are  thyreoproteid  and  thyreo-antitoxin  (C6HUN3O5). 
A  substance  has  also  been  found  in  the  thyroid,  principally  com- 
bined with  a  proteid,  although  also  free,  called  thyro-iodin  and 
iodo-thyrin,  containing  9.3  per  cent,  of  iodin  and  0.56  per  cent, 
of  phosphorus.  The  amount  of  iodin  in  each  gram  of  the  human 
adult  thyroid  varies  from  0.3  to  0.9. 

Structure. — The  thyroid  has  a  capsule  of  connective  tissue 
which  sends  off  septa  or  trabeculce  that  enclose  the  thyroid  vesicles 


---  Lumen  of  follicle. 
—  Connective  tissne. 

1  Epithelium  of  follicle. 

J 


FIG.  183.— From  section  through  thyroid  gland  of  child  (Bohm  and  Davidoff). 


(Fig.  183),  each  of  which  is  lined  by  cubical  epithelium  and  con- 
tains viscid,  colloid  liquid,  yellowish  in  color,  which  is  coagulated 
by  alcohol  and  stained  with  hematoxylin,  and  is  doubtless  secreted 
by  these  cells.  Red  blood-corpuscles  in  various  stages  of  disinte- 
gration and  white  corpuscles  are  also  found  in  these  vesicles. 
The  color  of  the  colloid  material  is  probably  due  to  hemoglobin. 
Around  the  vesicles  is  a  plexus  of  capillary  blood-vessels, 
which  is  also  found  between  the  vesicular  epithelium  and  the 
endothelium  of  the  lymph-spaces,  which  latter  surround  the  vesi- 
cles and  communicate  with  lymphatic  vessels.  Colloid  material, 


THE  THYROID  AND  PARATHYROID.  341 

identical  with  that  contained  in  the  vesicles,  has  been   found  in 
the  lymphatics. 

The  arteries  which  supply  the  thyroid  body  are  the  superior 
and  inferior  thyroid,  and  sometimes  the  thyroidea  media  or  ima, 
an  occasional  branch  of  the  innominate  or  aorta. 

The  nerves  are  from  the  middle  and  inferior  cervical  ganglia 
of  the  sympathetic. 

Functions. — In  recent  years  the  physiology  of  the  thyroid 
body  has  received  a  great  deal  of  attention,  and  important  addi- 
tions have  been  made  to  the  knowledge  of  its  function  by  a  study 
of  (1)  the  effects  of  its  disease  and  (2)  of  its  removal. 

Cretinism. — In  some  parts  of  Switzerland  and  elsewhere  on  the 
Continent  there  exists  a  disease  characterized  by  a  swelling  of  the 
thyroid,  termed  goiter,  together  with  "stunted  growth,  swelled 
abdomen,  wrinkled  skin,  wan  complexion,  vacant  and  stupid 
countenance,  misshapen  cranium,  idiocy,  and  comparative  insensi- 
bility." This  disease  is  cretinism,  and  those  suffering  from  it  are 
cretins.  This  condition  is  accompanied  by  disease  of  the  thyroid, 
as  manifested  by  the  goiter. 

Myxedema. — A  similar  condition  is  sometimes  seen  in  which 
the  striking  characteristic  is  the  appearance  of  the  skin,  which 
resembles  edema  ;  and  the  material  which  is  deposited  in  the  con- 
nective tissue  was  thought  to  be  mucin,  hence  the  name  myxedema. 
Although  there  is  more  mucin  than  in  ordinary  connective  tissue, 
still  the  material  here  is  not  altogether  mucin,  nor  is  it  true  edema 
— /.  <?.,  a  dropsical  effusion  into  the  cellular  tissue — but  a  hyper- 
plastic  and  modified  connective  tissue.  In  addition  to  this  condi- 
tion of  the  skin  there  is  also  a  slowness  of  gait,  an  apathy  of  mind, 
and  sometimes  tremors  and  twitchings  of  muscles. 

Operative  Myxedema. — When  the  thyroid  gland  becomes 
enlarged,  this  may  be  due  to  a  hypertrophy  of  the  vesicles,  paren- 
chymatous  goiter,  or  of  the  connective  tissue,  fibroid  goiter  ;  or  the 
vesicles  may  form  cysts,  cystic  goiter,  or  the  blood-vessels  may  be 
dilated,  pulsating  goiter,  or  the  vessels  may  be  enlarged,  and  with 
this  a  prominence  of  the  eyes,  palpitation  of  the  heart,  and  a  quick 
pulse,  exophthalmic  goiter  or  G raves' s  disease.  For  goiter,  one  of 
the  methods  of  treatment  is  the  removal  of  the  gland ;  when  this 
is  practised,  a  condition  of  myxedema  results,  operative  myxedema. 
The  removal  of  the  thyroid,  thyroidectomy ,  has  been  performed 
upon  dogs  with  a  fatal  result  in  all  cases,  occurring  so  soon  after 
the  operation — within  fourteen  days — that  the  changes  in  the  skin 
have  no  time  to  take  place,  but  tremors,  spasms,  and  convulsions 
occur.  One  remarkable  fact  was  discovered  by  Schiff,  who  per- 
formed as  many  as  sixty  thyroidectomies  on  dogs — namely,  that  if 
a  portion  of  a  thyroid  was,  before  the  operation,  grafted  under  the 
skin  or  into  the  peritoneal  cavity,  the  symptoms  described  did  not 
occur,  and  the  animals  did  not  die.  Horsley  removed  the  thyroid 
from  monkeys,  with  the  result  of  producing  myxedema. 


342  DUCTLESS  GLANDS. 

It  has  been  demonstrated,  as  already  stated,  that  grafting  a 
thyroid  or  part  of  it  into  an  animal  before  the  removal  of  its 
thyroid  will  prevent  the  myxedematous  symptoms.  It  is  interest- 
ing to  know  that  if,  later,  this  graft  is  removed,  the  symptoms  will 
then  supervene.  Injections  of  an  extract  of  the  thyroid  gland 
and  also  feeding  the  gland  itself  are  followed  by  the  same  results 
as  the  grafting  process. 

There  are  two  theories  which  have  been  advanced  to  explain 
the  results  of  removal  of  the  thyroid  :  (1)  autotoxication  and  (2) 
internal  secretion. 

Autotoxication. — This  theory  supposes  that  there  are  toxic  sub- 
stances normally  in  the  blood  which,  being  removed  or  rendered 
harmless  by  the"  thyroid,  accumulate  when  that  organ  is  removed 
and  produce  the  effects  that  follow  thyroidectomy.  In  support 
of  this,  it  is  stated  that  the  urine  of  animals  operated  on  is  more 
toxic  than  that  of  unope rated  animals,  and  that  their  blood  is  also 
toxic  for  others. 

Internal  Secretion. — We  have  already  seen  that  the  pan- 
creas, in  addition  to  the  pancreatic  juice,  which  is  its  external 
secretion,  also  produces  an  internal  secretion.  This  is  also  be- 
lieved to  be  true  of  the  thyroid,  and  it  is  this  secretion  which  is 
taken  up  by  the  blood  or  the  lymph  in  its  passage  through  the 
gland  and  carried  to  the  tissues,  where  it  is,  in  some  way  not  under- 
stood, connected  with  their  metabolic  processes.  From  the  dis- 
turbances in  the  nervous  system  and  connective  tissues  which  occur 
on  ablation  of  the  gland,  it  is  probably  especially  related  to  their 
metabolism.  When,  therefore,  after,  extirpation  of  the  thyroid  or 
in  cases  of  myxedema  where  the  gland  is  diseased,  injections  of  the 
extract  or  injections  of  the  gland  itself  are  followed  by  beneficial 
results,  it  is,  doubtless,  due  to  the  introduction  into  the  blood  of  this 
internal  secretion.  It  is  also  possible  that  some  of  the  toxic  products 
of  metabolism  may  be  destroyed  by  the  gland  or  its  secretion. 

Several  observers  have  maintained  that  the  thyroid  was  inti- 
mately connected  with  the  regulation  of  the  supply  of  blood  to 
the  head,  and  have  reasoned  thus  from  its  great  vascularity  and 
direct  connection  with  the  blood-vessels  of  the  head  ;  and  Cyon  has 
demonstrated  that  the  nerves  supplying  the  thyroid  when  stimu- 
lated lower  the  blood-pressure  in  the  carotid,  by  virtue  of  vaso- 
dilators, which  are  contained  in  the  trunks  of  the  nerves.  These 
nerves  are  called  into  action  when  the  cut  ends  of  the  vagi,  of  the 
depressors,  or  of  the  cardiac  branches  of  the  recurrent  laryngeal 
nerves  are  stimulated. 

To  which  of  the  constituents  of  the  thyroid  extract  its  effects 
are  due  is  still  a  mooted  question.  Indeed,  the  most  recent 
researches  seem  to  indicate  that  the  gland  forms  more  than  one 
substance,  each  one  having  its  own  action  ;  thus  there  seems  to  be 
no  doubt  that  both  iodothyrin  and  thyreo-antitoxin  are  produced, 


THE  THYROID  AND  PARATHYROID.  343 

although  at  the  present  time  the  iodothyrin  seems  to  be  regarded 
as  the  most  active  ingredient. 

Thyroid  extract  has  also  been  recommended  as  a  means  of 
treating  obesity,  on  the  ground  that  it  increases  metabolism ; 
there  is  undoubtedly  a  diminution  of  fat  in  its  use. 

The  thyroid  gland  has  been  used  in  the  treatment  of  goiter, 
myxedema,  etc.,  in  various  ways.  Thus  Schiff  and  Esselsberg,  in 
1884,  made  grafts  both  in  the  abdominal  cavity  and  in  the  cellular 
tissue.  Birch,  on  the  advice  of  Horsley,  transplanted  the  thyroid 
of  a  sheep  into  the  peritoneal  cavity  of  a  woman  suffering  with 
myxedema.  For  a  time  she  was  benefited,  but  the  gland  was 
absorbed  and  the  symptoms  returned.  In  1890  Pisenti  extracted 
the  juice  from  the  thyroid  and  injected  it  into  the  tissues ;  Gley 
was  the  first  to  use  this  method  on  the  human  subject  and  cured 
his  patient.  Horwitz,  in  1892,  demonstrated  that  the  gland  itself 
could  be  given  by  the  mouth  with  equally  good  results  as  when 
its  extract  was  injected,  and  later  the  extract  was  given  by  the 
mouth.  At  the  present  time  tablets  containing  the  fresh  gland 
of  the  sheep  are  used  for  goiter,  myxedema,  obesity,  etc. 

H.  O.  Nicholson  reports  the  case  of  a  child  cretin  in  which 
the  effects  of  thyroid  treatment  upon  the  bodily  and  mental  con- 
dition were  remarkably  rapid  and  complete.  At  the  age  of  two . 
years  and  eight  months  the  child  Avas  in  the  condition  of  well- 
marked  cretinism.  The  initial  dose  of  thyroid  powder  was  2^ 
grains,  once  daily ;  but  after  three  days,  on  account  of  diarrhea, 
this  was  reduced  to  1^  grains  for  several  weeks,  when  the  original 
dose  was  given.  After  four  months  of  treatment  a  photograph, 
with  which  the  article  is  illustrated,  showed  "a  bright,  happy, 
pretty  child,  to  all  appearances  normal,  both  physically  and 
mentally"  (Figs.  184,  185).  A  few  months  later  death  occurred 
during  a  malignant  attack  of  measles,  but  an  autopsy  could  not  be 
obtained.  In  the  etiology  the  author  lays  stress  on  the  fact  that 
the  child  seemed  normal  for  the  first  four  months  of  life,  at  the 
end  of  which  it  contracted  whooping-cough  lasting  four  months, 
and  then  it  was  seen  to  be  abnormal.  He  attributes  the  origin  of 
cretinism  to  the  attack  of  pertussis. 

We  are  indebted  to  M.  A.  Flourens,  of  Bordeaux,  for  a  very 
interesting  resume  of  thyroid  medication,  and  the  following  case 
is  taken  from  his  pamphlet : 

This  was  a  girl  of  twelve  years,  suffering  from  myxedema,  in 
whom  there  was  a  question  as  to  the  presence  of  a  thyroid.  She 
came  under  treatment  in  February,  1893.  The  disease  began 
when  she  was  nine  years  old. 

The  child  began  to  be  inattentive,  flighty,  and  especially  in- 
different. Her  memory  became  weakened  and  study  fatiguing. 
She  developed  a  state  of  torpor  and  did  not  care  to  play  with  her 
brother  and  sister.  Her  movements  were  slow  and  lazy,  a  laziness 
more  moral  than  physical,  especially  of  the  will,  for  if  compelled 


344 


DUCTLESS  GLANDS. 


to  move  she  could  take  walks  as  long  as  10  kilometers  without 
much  effort.  At  the  same  time  her  disposition  changed,  became 
"  sour,"  and  everything  annoyed  her.  In  endeavoring  to  counter- 
act the  feeling  of  cold  that  the  warmest  clothing  would  not  allay, 
she  would  sit  near  enough  to  the  open  hearth  to  burn  her  limbs. 

These  signs  of  intellectual  apathy  were  accompanied  by  physical 
symptoms.  The  skin  became  pale  and  the  face  swollen,  losing  its 
oval  shape  and  assuming  the  aspect  of  a  full  moon,  symptoms  so 
well  described  by  Gull  in  his  first  observations.  The  swelling 
extended  to  the  limbs  and  body,  becoming  hard  and  resisting,  not 


FIGS.  184,  185. — Illustrating  Nicholson's  article  on  thyroid  treatment  in  a  cretin 
(Arch,  of  Ped.,  June,  1900).     Fig.  184,  before  treatment ;  Fig.  185,  after  treatment. 

presenting  the  characteristic  pitting  of  edema.  The  skin  lost  its 
softness  and  the  trunk  and  limbs  were  affected  with  ichthyosis. 
The  hair  remained  long  and  silky.  There  was  no  change  in  the 
nails.  The  development  of  the  teeth  was  arrested,  these  being 
short,  as  if  buried  in  fungous  gums  from  which  emerged  only  the 
extremities  of  teeth.  This  was  more  noticeable  in  the  superior 
maxilla.  The  child  was  weighed  but,  unfortunately,  the  exact 
figures  were  lost.  They  were,  however,  very  high  for  a  child  of 
her  age.  Since  two  years  there  has  been  a  complete  arrest  of 
growth.  Her  height  was  about  4  feet  2-J-  inches. 


THE  THYROID  AND  PARATHYROID. 


345 


The  report  of  her  condition  in  October,  1894,  was  as  follows : 
The  treatment  was  continued  and  the  amelioration  persisted.  The 
edema  completely  disappeared,  the  teeth  had  grown,  and  there  was 
no  longer  the  spongy  condition  of  the  gums  of  the  superior  maxilla. 
The  intellectual  torpor  had  disappeared,  and  the  child  was  more 
lively ;  she  answered  intelligently  when  interrogated ;  she  no 
longer  had  the  sensation  of  cold.  She  had  grown  considerably. 
In  October,  1895,  the  menses  appeared,  the  general  condition  was 
excellent,  and  the  memory  had  returned. 

Figs.  186  and  187  show  a  case  of  goiter  which  was  treated 
with  thyroid  extract. 


w*. 


FIGS.  186,  187.— Case  of  goiter  before  aud  after  treatment  with  thyroid  extract 

(Flourens). 

Parathyroids. — These  are  four  small  glandular  bodies  situated 
one  on  the  lateral  and  one  on  the  mesial  surface  of  each  lobe  of 
the  thyroid.  They  consist  of  columns  of  granular  epithelium, 
with  vascular  connective  tissue  between  the  columns.  It  is  claimed 
by  some  that  after  removal  of  the  thyroid  these  bodies  become 
hypertrophied  and  perform  its  functions,  and  it  has  been  supposed 
that  when  after  thyroidectomy  the  usual  results  do  not  appear  it 
is  due  either  to  the  fact  that  some  of  the  thyroid  was  left,  or 
else  that  these  parathyroids  took  up  its  functions ;  this  is  Gley's 
explanation  in  the  case  of  rabbits,  in  which  ablation  of  the  thyroid 


346  DUCTLESS  GLANDS. 

is  usually  followed  by  negative  results ;  and  he  states  that  if  the 
parathyroids  are  removed  from  these  animals  together  with  the 
thyroid,  the  usual  results  appear.  On  the  other  hand,  Blumen- 
reich  and  Jacoby  state  that  it  makes  no  difference  whether  the 
parathyroids  are  included  or  excluded. 

THE  THYMUS. 

The  thymus  is  situated  behind  the  sternum,  and  extends  from 
the  fourth  costal  cartilage  to  the  lower  border  of  the  thyroid.  It 
is  about  5  cm.  long,  about  4  cm.  broad,  and  1  cm.  thick,  and  at 
birth  weighs  about  16  grams. 

The  thymus  reaches  its  full  size  at  the  end  of  the  second  year, 
at  which  time  it  decreases,  and  at  puberty  it  has  almost  wholly  dis- 


jliiiilla 


FIG.  188. — A  small  lobule  from  the  thymus  of  a  child,  with  well-developed  cortex, 
presenting  a  structure  similar  to  that  of  the  cortex  of  a  lymph-gland :  a,  hilus  ;  b, 
medullary  substance  ;  c,  cortical  substance ;  d,  trabecula ;  X  60  (Bohin  and  Davidoff ). 

appeared  ;  it  is,  therefore,  a  temporary  organ.  The  thymus  of  the 
calf  is  called  the  neck  or  throat-sweetbread,  while  the  pancreas 
is  the  belly-sweetbread. 

Chemical  Composition. — The  reaction  during  life  is  alka- 
line, but  acid  after  death,  due  to  sarcolactic  acid.  It  contains 
12.29  per  cent,  of  proteids,  together  with  adenin,  xanthin,  hypo- 
xanthin,  and  guanin.  lodin  exists  also  in  the  gland. 

Structure. — The  thymus  is  composed  of  two  lobes,  sometimes 
united  into  one  and  sometimes  separated  by  an  intermediate  lobe. 
It  presents  an  irregular  lobulated  appearance,  and  has  an  external 
capsule,  beneath  which  are  the  lobules,  separated  from  one  another 
by  connective  tissue,  in  which  are  the  blood-vessels  and  lymphatics. 
Each  lobule  is  made  up  of  a  cortex  and  medulla  ;  the  cortex  being 
composed  of  nodules  separated  by  trabeculce,  as  described  in  con- 
nection with  the  lymphatic  glands  (p.  332).  In  the  nodules  are 
lymphoid  cells  and  a  reticulum  (Fig.  188).  In  the  medullary 
portion  the  lymph-corpuscles  are  less  numerous,  but  there  are  here 


THE  SUPRARENAL  CAPSULES  OR  ADRENAL  BODIES.  347 

peculiar  cells,  the  concentric  corpuscles  of  Hassal  (Fig, ,189), 
which  consist  of  a  central  cell  around  which  flattened  epithelial 
cells  are  arranged  concentrically. 

The  arteries  which   supply  this  gland  are  derived   from   the 
and   the 


mammary 


A 


FIG.  189. — Hassal's  corpuscle  and  a  small 
portion  of  medullary  substance,  showing 
reticulum  and  cells,  from  tbymus  of  a  child 
ten  days  old  (Huber). 


internal 

superior  and  inferior  thyroid. 
The  nerves  are  from  the  pneu- 
mogastric  and  sympathetic. 

Function.— T  o  g  e  t  h  e  r 
with  other  glands  containing 
lymphoid  tissue,  the  thymus 
is  undoubtedly  a  source  of 
leukocytes;  and  because 
Watney  has  found  in  cells  of 
the  thymus  hemoglobin  vary- 
ing in  shape  from  granules  to 
masses  having  the  appearance 
of  red  blood-corpuscles,  and 
similar  cells  in  the  lymph 
coming  from  the  gland,  lie 
concludes  that  the  thymus  is 
one  of  the  sources  of  red  blood-corpuscles.  So  far  as  known,  no 
effects  are  produced  by  injecting  into  the  tissue  an  extract  of  the 
thymus,  nor  by  injecting  portions  of  the  gland  itself. 

THE  SUPRARENAL  CAPSULES  OR  ADRENAL  BODIES. 

These  are  flattened,  glandular  structures  situated  one  above  and 
one  in  front  of  the  upper  part  of  each  kidney.  In  length  each 
is  about  3.5  cm.,  in  width  2.5  cm.,  and  in  thickness  1  cm.,  the 
right  being  smaller  than  the  left.  They  present  a  cocked-hat 
appearance.  The  weight  of  each  is  about  4  grams. 

Chemical  Composition. — These  bodies  contain  proteids, 
cell-globulin  and  nucleoproteid,  extractives  such  as  occur  in  the 
other  ductless  glands,  salts,  of  which  one  is  potassium  phos- 
phate, hippuric  and  taurocholic  acids.  The  presence  of  a  reducing 
substance  similar  to  jecorin  of  the  liver  has  been  claimed  by  some, 
but  denied  by  others. 

Structure. — There  is  a  marked  difference  between  the  struct- 
ure of  the  suprarenal  capsules  and  the  other  ductless  glands  which 
we  have  considered.  Each  capsule  is  invested  with  a  fibrous  cap- 
sule. On  section  (Fig.  190)  it  is  found  to  consist  of  a  cortical  portion 
or  cortex,  the  greater  part  of  the  gland,  which  is  yellow  in  color 
and  presents  a  striated  appearance  ;  and  a  medullary  portion  or 
medulla,  which  is  of  a  dark-brown  or  dark-red  color.  The  capsule 
gives  off  septa,  which  so  divide  the  cortex  as  to  leave  spaces,  filled 
with  granular,  polyhedral  cells,  some  of  them  containing  oil- 


348 


DUCTLESS  GLANDS. 


globules,  each  cell  being  provided  with  a  nucleus.  Just  beneath 
the  capsule  these  cells  form  the  zona  glomerulosa  and  zona  fascicu- 
lata,  and  still  deeper,  the  zona  recticularis. 

In  the  medulla  the  fibrous  stroma  is  arranged  so  as  to  form 
bundles  around  the  veins,  which  are  very  numerous  in  this  portion 
of  the  gland.  In  the  spaces  are  irregular,  granular  cells,  some 


Capsule. 


Zona  glomerulosa. 


Zona  fasciculata. 


Zona  reticularis. 


FIG.  190. — Section  of  suprarenal  cortex  of  dog ;  X  120  (Bohm  and  Davidoff). 

of  which  are  branched  ;  these  are  stained  brown  by  chromic  acid,, 
and  the  material  taking  the  stain  is  called  a  chromogen. 

The  arteries  supplying  the  suprarenal  capsules  are  derived 
from  the  aorta,  phrenic,  and  renal,  and  break  up  into  capillaries 
in  the  septa  of  the  cortical  portion,  which  discharges  its  veins  in 
the  medulla,  finally  becoming  the  suprarenal  vein,  which  on  the 
right  side  enters  the  inferior  vena  cava,  and  on  the  left  the  renal 
vein.  The  nerves  are  derived  from  the  solar  and  renal  plexuses,. 


THE  SUPRARENAL   CAPSULES  OR  ADRENAL  BODIES.   349 

and  from  the  phrenic  and  pneumogastric,  and  upon  these  there  are 
ganglia. 

Functions. — Addison's  disease  is  defined  as  ua  disease 
marked  by  a  peculiar  bronze-like  pigmentation  of  the  skin,  early 
and  severe  prostration,  and  progressive  anemia,  and  usually  ending 
fatally.  It  is  due  to  tubercular  disease  of  the  suprarenal  cap- 
sules." 

In  1855  Addison  discovered  the  connection  of  the  disease 
above  described  with  pathologic  changes  in  the  suprarenal  bodies, 
and  removal  of  both  of  them  experimentally  by  Brown-Se'quard 
produced  a  similar  condition,  excepting  the  discoloration  of  the 
skin,  and  a  fatal  result,  usually  within  twelve  hours.  It  was  sur- 
mised that  the  absence  of  pigmentation  was  due  to  the  speedy 
death.  Since  then  the  capsules  have  been  crushed,  with  the  effect 
of  producing  the  skin  changes.  Within  recent  years  the  suprarenal 
capsules  have  been  frequently  removed,  always  with  a  fatal  result 
within  three  days,  and  the  blood  of  such  animals  when  injected 
into  other  animals  whose  capsules  have  been  removed  is  toxic, 
while  if  normal  blood  is  injected  into  the  veins  of  the  latter  their 
life  is  prolonged.  It  is  supposed  from  this  that  the  function  of 
the  suprarenal  capsule  is  to  destroy  some  toxic  substance  in  the 
blood  ;  this  accumulates  when  these  bodies  are  removed,  and  such 
blood  is  poisonous.  This  is  the  autotoxication  theory. 

Schafer  has  injected  into  animals  watery  and  glycerin  extracts 
of  the  capsules,  the  results  varying  with  the  amount  injected  and 
the  animal  experimented  upon.  In  the  cat  and  dog  large  doses 
produce  quickened  and  augmented  heart-beat,  shallow  and  rapid 
respiration,  and  fall  of  temperature.  Intravenous  injection  of 
suprarenal  extract  produces,  according  to  Schafer,  a  powerful 
physiologic  action  upon  the  muscular  system  in  general,  greatly 
prolonging  the  contraction  of  a  muscle  in  response  to  a  single  ex- 
citation of  its  nerve  (Fig.  191),  but  especially  upon  the  muscular 
walls  of  the  blood-vessels  and  heart.  A  certain  amount  of  action 
is  also  manifested  upon  some  of  the  nerve-centers  in  the  bulb, 
especially  in  the  cardio-inhibitory  center,  and  to  a  less  extent  upon 
the  respiratory  center.  The  blood-pressure  is  greatly  increased, 
due  to  contraction  of  the  arterioles,  the  extract  acting  upon  the 
muscular  coat  of  these  vessels  directly,  and  not  through  the  vaso- 
motor  center. 

The  active  principle  wrhich  produces  these  physiologic  effects  is 
obtained  from  the  medulla,  and  it  has  been  demonstrated  that  so 
small  an  amount  as  TOOOOOO  part  of. a  gram  per  kilo  of  body- 
weight,  equivalent  to  T^OTO  gmm  f°r  an  adult  man,  will  produce 
distinct  physiologic  results  upon  the  heart  and  arteries ;  but 
whether  it  is  the  alkaloidal  substance,  epinephrin,  isolated  by  Abel, 
or  the  crystal lizable  one  obtained  by  Takamineand  called  adrenalin, 
has  not  yet  been  determined. 

Schafer  draws  the  following  conclusions  :  "  It  may  be  consid- 


350 


DUCTLESS  GLANDS. 


ered  probable  that  the  suprarenal  capsules  are  continually  secreting 
into  the  blood  an  active  material,  which  although  present  in  that 
fluid  only  in  minute  quantities,  may  yet  be  sufficient  to  produce 
very  distinct  effects  upon  the  metabolic  processes  of  muscular 
tissue,  and  especially  the  muscular  tissue  of  the  vascular  system. 
It  has,  in  fact,  been  stated  by  Cybulski,  and  this  statement  has 
been  confirmed  by  Langlois  and  by  Biedl,  that  the  blood  of  the 
suprarenal  vein  contains  a  sufficient  amount  of  the  active  principle 
of  suprarenal  extract  to  produce  a  marked  rise  of  blood-pressure 
when  intravenously  injected.  I  have,  in  spite  of  careful  experi- 
ments, not  been  able  to  confirm  this  statement.  Nor  is  it  easy  to 
understand  how  it  can  be  true,  since  such  blood  is  constantly 
flowing  into  the  vena  cava  in  larger  quantity  than  these  observers 


FIG.  191. — Effect  of  suprarenal  extract  upon  muscle-contraction  in  the  frog :  A, 
normal  muscle-curve  of  gastrocnemius ;  B,  curve  taken  during  suprarenal  poison- 
ing, but  otherwise  under  the  same  conditions  as  A  ;  time  tracing  ;  100  per  second 
(Schafer). 


injected.  But  whether  we  are  able  to  show  it  experimentally  or 
not,  there  is  very  little  doubt  of  the  fact  that  the  materials  found 
pass  somehow  or  other  into  the  blood  ;  and  when  we  compare  the 
results  of  suprarenal  injection  with  the  effects  obtained  from  the 
removal  and  from  disease  of  these  organs,  we  can  come  to  no 
other  conclusion  than  that  we  have  before  us  a  notable  instance  of 
internal  secretion  ;  and  that  the  effect  of  such  secretion  passed 
into  the  blood  is  beneficial  to  the  muscular  contraction  and  tone 
of  the  cardiac  and  vascular  walls,  and  even  of  the  skeletal  mus- 
cles, appears  very  evident  from  the  results  both  of  the  removal  of 
the  organs  and  of  injection  of  their  extracts." 

Although  in  one  case  of  Addison's  disease  in  which  fresh  cap- 
sules of  the  calf  were  administered  there  was  apparent  benefit, 
the  evidence  is  still  too  meager  to  draw  any  general  conclusions  as 
to  its  usefulness  in  the  treatment  of  this  affection. 


THE  PITUITARY  BODY.  351 

THE  PINEAL  GLAND. 

This  gland,  also  known  as  epiphysis  cerebri,  is  situated  in  the 
brain  behind  the  posterior  commissure  and  between  the  anterior 
corpora  quadrigemina.  It  is  reddish  gray  in  color,  about  0.8 
ram.  long  and  0.6  mm.  wide,  larger  in  childhood  than  in  adult 
life,  and  in  the  female  than  in  the  male. 

Structure. — It  is  composed  of  connective  tissue  and  follicles 
lined  with  epithelium.  In  these  follicles  is  a  viscid  fluid  with 
brain-sandy  acervulus  cerebri,  which  consists  of  calcium  phosphate 
and  carbonate,  magnesium  and  ammonium  phosphate,  with  some 
organic  matter.  The  pineal  gland  exists  in  the  fetal  brain  in  the 
form  of  a  follow  protrusion  from  the  posterior  part  of  the  roof 
of  the  interbrain.  It  is  regarded  by  some  as  an  atrophied  third 
eye.  Schafer  says  that  in  the  chameleon  and  some  other  reptiles 
the  pineal  gland  is  better  developed,  and  is  connected  with  a 
rudimentary  median  eye  of  invertebrate  type,  placed  upon  the 
upper  surface  of  the  head. 

Its  function  is  unknown. 

THE  PITUITARY  BODY. 

This  body  is  also  known  as  hypophysis  cerebri.  It  is  situated 
on  the  sella  Turcica  of  the  sphenoid  bone,  is  reddish  gray  in  color, 
and  weighs  from  4  dgm.  to  8  dgm. 

Structure. — It  consists  of  two  lobes,  the  anterior  being  the 
larger.  This  lobe  is  developed  as  a  hollow  or  tubular  prolongation 
of  the  epiblast  of  the  buccal  cavity,  and  consists  of  vesicles  and 
alveoli  lined  with  columnar  epithelium,  which  is  in  some  places 
ciliated.  In  the  alveoli  is  sometimes  found  a  colloid  substance 
similar  to  that  in  the  thyroid,  and  around  the  alveoli- are  lymph- 
atics and  capillaries.  Indeed,  the  resemblance  in  structure  be- 
tween the  pituitary  body  and  the  thyroid  has  led  to  the  supposi- 
tion that  physiologically  they  are  related. 

The  posterior  lobe  has  a  different  origin  from  the  anterior.  It 
is  developed  from  the  floor  of  the  third  ventricle,  and  in  fetal  life 
communicates  with  this  cavity  through  the  infundibulum.  It 
consists  in  the  adult  principally  of  vascular  connective  tissue,  con- 
taining but  few  nervous  elements. 

Function. — The  pituitary  body  has  been  repeatedly  removed 
from  dogs  and  cats,  death  resulting  within  two  weeks.  The 
symptoms  following  removal  are  (1)  diminution  of  body-tem- 
perature ;  (2)  loss  of  appetite  and  lassitude  ;  (3)  muscular  twitch- 
ings,  tremors,  and  spasms  ;  (4)  dyspnea.  Some  of  these  symptoms 
are  improved  by  injections  of  extract  of  the  pituitary  body.  It 
will  be  remembered  that  some  of  these  symptoms  occurred  after 
ablation  of  the  thyroid  (p.  341),  and  it  is  stated  that  the  pituitary 
body  becomes  enlarged  after  thyroidectomy.  Rogowitsch  thinks 


352  RESPIRATION. 

that  this  accounts  for  the  failure  to  produce  fatal  results  in  rabbits 
by  the  removal  of  the  thyroid,  the  pituitary  body  being  especially 
well  developed  in  that  animal.  It  is  stated  by  some  that  acromey- 
aty)  a  disease  characterized  by  hypertrophy  of  the  bones  of  the 
face  and  extremities,  and  also  of  the  skin,  is  associated  with 
enlargement  and  degeneration  of  the  pituitary  body.  Dr.  Kinnicutt 
states  that  in  34  recorded  cases  of  acromegaly,  with  full  autopsy, 
a  microscopic  lesion  of  the  pituitary  body  has  been  found  in  every 
instance,  and  in  the  majority  of  cases  it  has  proved  to  be  either  a 
simple  hyperplasia  or  a  tumor  growth  of  some  kind.  Others  have 
not  found  these  lesions  in  cases  of  enlargement  of  the  gland,  but 
rather  a  persistence  of  the  thymus. 

There  seems  to  be  no  valid  reason  for  concluding  that  the 
thyroid  and  the  pituitary  body  have  any  physiologic  relation  with 
each .  other.  Injections  of  extracts  of  the  pituitary  body  cause 
great  increase  in  the  force  of  the  heart's  beat,  and  also  an  increase 
in  blood-pressure  by  contracting  the  arterioles ;  that  of  the  thyroid 
does  neither. 

That  the  pituitary  body  furnishes  an  internal  secretion  seems 
to  be  beyond  question,  and  this  has  the  effect  of  increasing  the 
contraction  of  the  heart  and  arteries,  and  also  of  influencing  the 
metabolism  of  the  bones  and  nervous  system,  but  just  how  this  is 
brought  about  is  not  determined. 

THE  CAROTID  AND  THE  COCCYGEAL  GLANDS. 

The  carotid  gland  is  situated  at  the  bifurcation  of  the  common 
carotid  artery,  and  the  coccygeal  gland  or  Luschka's  gland  is 
situated  in  front  of  the  tip  of  the  coccyx,  just  above  the  attachment 
of  the  sphincter  ani.  These  glands  are  collections  of  small  arteries 
enclosed  in  granular  polyhedral  cells,  the  whole  being  enclosed 
in  a  capsule.  Into  the  coccygeal  gland  sympathetic  nerves  pass. 
Macalister  regards  it  as  consisting  of  "  the  condensed  and  con- 
voluted metameric  dorsal  arteries  of  the  caudal  segments  embedded 
in  tissue  which  is  possibly  a  small  persisting  fragment  of  the 
neurenteric  canal." 

The  function  of  these  glands  is  unknown,  if,  indeed,  they 
possess  any. 

RESPIRATION. 

One  of  the  most  important  processes  carried  on  in  the  body  is 
that  by  which  the  tissues  receive  oxygen.  In  animals  whose 
structure  is  exceedingly  simple,  and  so  constituted  that  all  portions 
of  their  bodies  are  bathed  by  the  oxygen-carrying  medium,  the 
oxygen  is  directly  absorbed ;  but  in  those  in  which  there  are 
tissues  remotely  situated  as  regards  this  medium,  some  provision 
must  be  made  for  conveying  the  oxygen  from  the  medium  to  the 


THE  NOSE.  '  353 

tissues.  This  condition  exists  in  man,  many  of  whose  tissues  are 
so  deeply  situated  that  without  such  provision  the  maintenance 
of  life  would  be  impossible.  In  man  this  medium  is  the  blood. 
But  additional  provision  must  be  made  for  the  renewal  of  the 
oxygen  abstracted  by  the  tissues.  That  part  of  the  process  by 
which  the  tissues  take  oxygen  from  the  blood  is  internal  respiration, 
and  that  part  by  which  the  renewal  is  accomplished  is  external 
respiration.  Ordinarily,  when  respiration  is  spoken  of  without 
qualification  it  is  external  respiration  that  is  referred  to. 

Respiratory  Apparatus. — The  group  of  organs  concerned 
in  external  respiration  is  collectively  spoken  of  as  the  respiratory 
apparatus,  which  consists  of  the  nose,  larynx,  trachea,  bronchi, 
lungs,  and  thorax. 

THE  NOSE. 

The  nose  is  the  beginning  of  the  air-passages,  for  although  it 
is  regarded  by  many  as  the  organ  of  smell  only,  it  has  another 
function  as  well.  The  mouth  belongs  to  the  alimentary  canal,  and 
should  be  opened  only  to  take  in  food  or  to  speak,  never  to  take 
in  air.  The  proper  channel  for  the  admission  of  air  is  the  nose, 
and  the  use  of  the  mouth  for  this  purpose  is  not  physiologic. 
Indeed,  man  is  said  to  be  the  only  animal  that  breathes  through 
the  mouth.  If  the  nursing  child  should  attempt  to  use  its  mouth 
for  the  admission  of  air  to  the  lungs,  sucking  could  not  be  performed 
without  great  difficulty,  and  after  a  few  moments  the  child  would 
be  compelled  to  let  go  the  breast  in  order  not  to  suffocate. 

Mouth-breathing". — There  is  no  more  pernicious  habit,  so 
far  as  health  is  concerned,  than  breathing  through  the  mouth.  If 
this  is  due  to  habit  and  to  nothing  else,  it  may  be  overcome ;  but 
if,  as  is  often  the  case,  it  is  due  to  some  diseased  condition  of  the 
nose,  or  to  the  presence  in  the  nasal  cavities  of  tumors,  or  to  the 
existence  of  enlarged  tonsils,  its  relief  can  be  accomplished  only 
by  surgical  means.  The  function  of  the  nose  in  respiration  is  to 
warm  the  air  and  to  filter  out  from  it  dust  and  other  extraneous 
matter  which  would  otherwise  enter  the  air-passages  and  cause 
irritation.  When  air  is  taken  in  by  the  mouth  these  beneficial 
results  do  not  occur. 

Mouth-breathing  causes  dryness  of  the  mouth  and  the  pharynx, 
which  condition  is  very  noticeable  on  awaking  from  sleep.  The 
mucous  membrane  becomes  congested  and  inflammation  is  likely 
to  follow.  A  chronic  inflammatory  condition  of  the  larynx  may 
also  result  from  this  cause,  and  the  evidence  is  very  conclusive 
that  the  hearing  becomes  affected  in  these  cases.  The  deformity 
known  as  pigeon-breast  is  not  an  uncommon  sequel.  Indeed,  the 
consequences  of  mouth -breathing  are  numerous,  widespread,  and 
serious,  and  the  subject  has  never  received  the  attention  which  its 
importance  demands. 

23 


354 


RESPIRATION. 


THE   LARYNX. 

This  organ  (Figs.  192,  193)  is  situated  at  the  upper  part  of  the 
neck,  behind  and  below  the  base  of  the  tongue.  It  is  composed  of 
nine  cartilages,  which  are  connected  by  ligaments. 

Cartilages. — These  are  the  thyroid,  cricoid,  arytenoid  (two), 
cornicula  laryngis  (two),  cuneiform  (two),  and  epiglottis. 

The  thyroid  is  the  largest  of  all  the  laryngeal  cartilages,  and 
the  angle  of  its  two  alee  forms  the  prominence  in  the  front  of  the 
throat,  Adam's  apple  or  pomum  Adami. 


FIG.  192. — Articulations  and  liga- 
ments of  the  larynx,  anterior  view : 
A,  hyoid  bone,  with  a  its  greater, 
and  a'  its  lesser  cornua ;  1-5,  liga- 
ments ;  6,  lateral  cricothyroid  artic- 
ulation ;  7,  junction  of  cricoid  and 
trachea  (Testut). 


FIG.  193. — Articulations  and  ligaments 
of  the  larynx,  posterior  view :  A,  hyoid ; 
B,  thyroid,  with  6  and  b'  its  cornua ;  C,  cri- 
coid ;  D,  arytenoids  ;  E,  cartilages  of  San- 
torini ;  F,  epiglottis ;  G,  trachea  ;  1-6,  liga- 
ments; 2,  opening  for  superior  laryngeal 
artery;  7,  junction  of  trachea  and  cricoid 
(Testut). 


The  cricoid  is  ring-shaped.  The  arytenoids  articulate  with  the 
cricoid  cartilage,  while  to  the  summit  of  these  are  attached  the 
cornicula  laryngis  or  cartilages  of  Santorini. 

The  cuneiform  cartilages  or  cartilages  of  Wrisberg  are  two 
small  bodies,  one  in  each  fold  of  the  mucous  membrane  extending 
from  the  apex  of  the  arytenoid  to  the  epiglottis,  the  aryteno-epi- 
glottic  fold. 

The  epiglottis  is  behind  the  tongue,  in  front  of  the  opening  of 
the  larynx.  Its  position  is  vertical  during  respiration,  but  during 


THE  LARYNX.  355 

a  part  of  the  act  of  deglutition  it  is  carried  backward  and  closes 
the  laryngeal  opening. 

The  cartilages  of  the  larynx  are  hyaline,  except  the  cornicula 
laryngis,  cuneiform,  and  epiglottis,  which  consist  of  yellow  fibro- 
cartilage,  and,  being  hyaline,  do  not  become  calcined. 

Muscles. — Of  these  there  are  two  sets — extrinsic,  which  arise 
outside  the  larynx,  and  intrinsic,  which  arise  within  the  larynx 
and  are  also  inserted  within  it. 

Extrinsic  Muscles. — These  may  be  subdivided  into  the  depressors 
and  elevators  and  exist  in  pairs. 

The  depressor  muscles  of  the  larynx  and  hyoid  bone  are  :  Sterno- 
hyoid,  which  arises  from  the  clavicle  and  sternum,  and  is  inserted 
into  the  hyoid  bone  ;  sternothyroid,  which  arises  from  the  sternum 
and  cartilage  of  the  first  rib,  and  is  inserted  into  the  ala  of  the 


FIG.  194. — Diagram  to  illustrate  the  thyro-arytenoid  muscles ;  the  figure  repre- 
sents a  transverse  section  of  the  larynx  through  the  bases  of  the  arytenoid  carti- 
lages :  Ary,  arytenoid  cartilage  ;  p.m,  processus  muscularis ;  p.v,  processus  vocalis ; 
Th,  thyroid  cartilage;  c.v,  vocal  cords;  Oe  is  placed  in  the  esophagus;  m.thy.ar.i, 
internal  thyro-arytenoid  muscle;  m.thy.ar.e,  external  thyro-arytenoid  muscle; 
m.thy.ar.ep,  part  of  the  thyro-ary-epiglottic  muscle,  cut  more  or  less  transversely; 
m.ar.t,  transverse  arytenoid  muscle  (redrawn  from  Foster). 

thyroid  cartilage;  thyrohyoid,  which  appears  like  a  continuation 
of  the  sternothyroid,  and  arises  from  the  side  of  the  thyroid  and 
is  inserted  into  the  hyoid  bone ;  omohyoid,  which  arises  from  the 
upper  border  of  the  scapula  and  is  inserted  into  the  hyoid  bone. 

The  action  of  this  group  of  muscles  is  to  depress  the  larynx 
and  hyoid  bone  at  the  close  of  deglutition ;  these  structures 
having  previously  been  drawn  up  with  the  pharynx.  The  omo- 
hyoid  by  carrying  the  hyoid  backward,  as  well  as  depressing  it, 
aids  in  performing  the  act  of  sucking.  The  thyrohyoid  raises  the 
thyroid  cartilage  as  well  as  depresses  the  hyoid  bone. 

The  elevators  of  the  larynx  and  hyoid  bone  are  the  digastric, 
which  arises  from  the  mastoid  process  of  the  temporal  bone  and 
from  near  the  symphysis  of  the  lower  jaw,  and  is  attached  to  the 
hyoid  bone  by  a  fibrous  loop ;  stylohyoid,  which  arises  from 
the  styloid  process  of  the  temporal  bone,  and  is  inserted  into 
the  hyoid ;  mylohyoid,  which  arises  from  the  mylohyoid  ridge  of 


356 


RESPIRATION. 


10- 


- 11 


the  lower  jaw,  and  is  inserted  into  the  hyoid  bone;  and  genio- 

hyoid,  which  arises  from  the  inferior  genial  tubercle  of  the  lower 

jaw,  and  is  inserted  into  the  hyoid  bone. 

The  action  of  this  group  of  muscles  is  to  raise  the  hyoid  bone 

and  the  larynx  during  deglutition ;  or  if  the  hyoid  bone  is  de- 
pressed and  fixed,  their  contrac- 
tion depresses  the  lower  jaw. 

Intrinsic  Muscles  (Figs.  194, 
195). — These  are  eight  in  num- 
ber : 

(1)  Gricoihyroid. — This  mus- 
cle arises  from  the  front  and  side 
of  the  cricoid  cartilage,  and  is 
inserted  into  tlje  lower  border 
of  the  thyroid  and  the  anterior 
border  of  the  lower  cornua.    The 
action  of  the  two  muscles  is  to 
make    tense   and    elongate   the 
vocal  cords.     Their  action  will 
be  better  understood  after  a  con- 
sideration of  the  thyrohyoid  mus- 
cles. 

(2)  Crico-arytenoideus  Posti- 
cu3. — It  arises  from  the  posterior 
surface  of  the  cricoid,  and  is  in- 
serted into  the  muscular  process 
of  the  base  of  the  arytenoid.  The 
action  of  the  two  muscles  is  to  ro- 
tate outward  the  arytenoid  carti- 
lages, and  thus  separate  and  make 
tense  the  vocal  cords  and  open  the 
glottis. 

(3)  Crico-arytenoideus     Lat- 
eralis. — This  muscle  has  its  ori- 
gin from  the  upper  border  of 
the  side  of  the  cricoid  cartilage, 
and   is   inserted    into   the   mus- 
cular process  of  the  arytenoid. 
The  action  of  the  pair  of  mus- 
cles is   to  rotate  the  arytenoid 

cartilages  inward,  approximating  the  vocal  cords  and  closing  the 
glottis. 

(4)  Arytenoideus. — This  is  a  single  muscle  and  arises  from  the 
posterior  surface  and  outer  border  of  one  arytenoid  cartilage,  and 
is  inserted  into  the  same  parts  of  the  other  arytenoid.  Its  action 
is  to  approximate  the  arytenoid  cartilages  and  close  the  glottis, 
especially  at  the  posterior  portion. 


17 


FIG.  195. — Larynx  and  its  lateral  mus- 
cles after  removal  of  the  left  plate  of  the 
thyroid  cartilage :  1,  thyroid  cartilage  ; 
2,  thyro-epiglottic  muscle  ;  3,  cartilage 
of  Wrisberg  ;  4,  ary-epiglottic  muscle  ; 
5,  cartilage  of  Santorini ;  6,  oblique  ary- 
tenoid muscles ;  7,  thyro-arytenoid  mus- 
cle ;  8,  transverse  arytenoid  muscle ;  9, 
processus  muscularis  of  arytenoid  car- 
tilage; 10,  lateral  crico-arytenoid  mus- 
cle; 11,  posterior  crico-arytenoid  mus- 
cle ;  12,  cricothyroid  membrane  ;  13,  cri- 
coid cartilage ;  14,  attachment  of  crico- 
thyroid muscle ;  15,  articular  surface  for 
the  inferior  cornu  of  the  thyroid  car- 
tilage ;  16,  cricotracheal  ligament ;  17, 
cartilages  of  trachea ;  18,  membranous 
part  of  trachea  (Stoerk). 


THE  LARYNX.  357 

(5)  Thyro-arytenoideus. — This  muscle  arises  from  the  angle  of 
the  thyroid  and  the  cricothyroid  membrane,  and  is  inserted  into 
the  arytenoid  cartilage.     It  consists  of  two  portions,  or  fasciculi  : 
An  inner,  which  is  inserted  into  the  vocal  process  of  the  arytenoid 
and   is  adherent  to  the  true   vocal  cord  ;  and  an  outer  portion, 
which  is  inserted  into  the  muscular  process.     The  action  of  the 
two  muscles  as  a  whole  is  to  draw  the  arytenoid  cartilages  toward 
the  thyroid,  shortening  and  relaxing  the  vocal  cords ;  the  inner 
fasciculus  acting  alone  modifies  the  elasticity  and  tension  of  the 
vocal  cords,  while  the  outer  rotates  the  arytenoid  cartilages  inward 
and  approximates  the  cords. 

(6)  Thyro-epiglottideus. — It  arises  from  the  angle  of  the  thyroid 


2 


16 -J 


17 

FIG.  196. — The  laryugoscopic  image  in  easy  breathing:  1,  base  of  the  tongue;  2, 
median  glosso-epiglottic  ligament ;  3,  vallecula ;  4,  lateral  glosso-epiglottic  ligament ; 
5,  epiglottis  ;  6.  cushion  of  epiglottis;  7,  cornu  major  of  hyoid  bone;  8,  ventricular 
band,  or  false  vocal  cord  ;  9,  true  vocal  cord  ;  opening  of  the  ventricle  of  Morgagni 
seen  between  8  and  9;  10,  folds  of  mucous  membrane;  11,  sinus  pyriformis;  12,  car- 
tilage of  Wrisberg ;  13,  aryteno-epiglottic  fold ;  14,  rima  glottidis ;  15,  arytenoid 
cartilage  ;  16,  cartilage  of  Santorini ;  17,  posterior  wall  of  pharynx  (Stoerk). 

cartilage,  and  is  inserted  into  the  aryteno-epiglottic  fold  and  the 
margin  of  the  epiglottis.  The  action  of  these  muscles  is  to  depress 
the  epiglottis,  and,  by  virtue  of  some  of  the  fibers  which  spread 
out  upon  the  outer  surface  of  the  sacculus  laryngis,  to  compress  it. 

(7)  ,Aryteno-epiglottideus  Superior. — This  arises  from  the  apex 
of  the  arytenoid,  and  its  fibers  disappear  in  the  aryteno-epiglottic 
fold.     The  action  of  the  pair  is  to  constrict  the  opening  of  the 
larynx  during  deglutition. 

(8)  Aryteno-epiglottideus   Inferior. — This    muscle    also   arises 
from  the  arytenoid,  and  spreads  out  upon  the  inner  surface  of  the 
sacculus  laryngis,  and  the  action  of  the  pair  is  to  compress  the 
sacculus. 

Gray,  to  whom  we  are   indebted  for  the  description  of  the 


358 


RESPIRATION. 


Jl 


larynx  and  other  anatomic  structures,  in  considering  the  action  of 
these  muscles,  says  that  they  may  be  conveniently  divided  into 
two  groups,  viz.,  1 .  Those  which  open  and  close  the  glottis ;  2. 
Those  which  regulate  the  degree  of  tension  of  the  vocal  cords. 

1.  The  muscles  which  open  the  glottis  are  the  crico-arytenoidei 
postici,  and  those  which  close  it  are  the  arytenoideus  and  the  crico- 
arytenoidei  laterales.  2.  The 
muscles  which  regulate  the 
tension  of  the  vocal  cords  are 
the  crico-thyroidei,  which  tense 
and  elongate  them ;  and  the 
thyro-arytenoidei,  which  relax 
and  shorten  them.  The  thyro- 
epiglottideus  is  a  depressor  of 
the  epiglottis,  and  the  aryteno- 
epiglottidei  constrict  the  supe- 
rior aperture  of  the  larynx, 
compress  the  sacculi  laryngis, 
and  empty  them  of  their  con- 
tents. 

Interior.— If  the  larynx  is 
inspected  from  above,  looking 
downward  (Fig.  196),  it  will  be 
seen  that  its  opening  is  bounded 
in  front  by  the  epiglottis,  behind 
by  the  inter arytenoid  fold,  con- 
sisting of  mucous  membrane, 
connecting  the  arytenoid  carti- 
lages, and  the  aryteno-epiglottic 
folds,  also  mucous  membrane, 
which  connect  the  sides  of  the 
epiglottis  and  the  arytenoid  car- 
tilages. The  cartilages  of  San- 
torini  and  Wrisberg  make  prom- 
inences in  these  folds. 

The  cavity  of  the  larynx 
(Fig.  197)  extends  from  its 
opening  to  the  lower  border  of 


14 


FIG.  197. — Vertical  transverse  section 
of  the  larynx:  1,  posterior  face  of  epiglot- 
tis, with  1',  its  cushion ;  2,  aryteno-epi- 
glottic fold  ;  3,  ventricular  band,  or  false 
vocal  cord  ;  4.  true  vocal  cord ;  5,  central 
fossa  of  Merkel ;  6,  ventricle  of  larynx, 
with  6',  its  ascending  pouch;  7,  anterior 
portion  of  cricoid ;  8,  section  of  cricoid ; 
9,  thyroid,  cut  surface ;  10,  thyrohyoid 
membrane;  11,  thyrohyoid  muscle;  12, 
aryteno-epiglottic  muscle ;  43,  thyro-ary- 
tenoid  muscle,  with  13',  its  inner  division, 
contained  in  the  vocal  cord  ;  14,  cricothy- 
roid  muscle;  15,  subglottic  portion  of 
larynx ;  16,  cavity  of  the  trachea  (after 
Testut). 


the  cricoid  cartilage.  In  look- 
ing into  it  there  will  be  seen 
the  inferior  or  true  vocal  cords, 
vocal  bands  or  ligaments,  the  portions  which  approximate  the  most 
closely,  and  between  them  a  space  or  fissure,  the  glottis  or  rimaglot- 
tidis.  The  term  rima  glottidis  is  applied  by  some  authors  to  the 
boundary  of  the  space,  and  by  others  to  the  space  itself,  using  it 
synonymously  with  glottis.  Above  the  true  vocal  cords  are  the 
superior  or  false  vocal  cords,  and  between  the  true  and  false  on 


THE  LARYNX. 


359 


each  side  is  the  ventricle  of  Morgagni,  the  anterior  part  of  which 
connects   with   the   sacoulus   laryngis,    or   laryngeal  pouch}   into 


Glands  in  false      — 
vocal  cord. 


Ventricle  of 
Morgagni 

Stratified  pavement 
epithelium  of  true    \~" 
vocal  cord.  \ 


Stratified  ciliated  col- 
umnar epithelium. 


Glands.  — 


Muscle. 


~  Muscle. 


FIG.  198. — Vertical  section  through  the  mucous  membrane  of  the  human  larynx ; 
X  5  (Bohm  and  Davidoff). 


which  discharge  60  or  70  glands  situated  in  the  submucous  areolar 
tissue. 


360 


RESPIRATION. 


The  glottis  and  the  true  vocal  cords  demand  a  somewhat  more 
detailed  description  than  given  above,  owing  to  their  importance 
in  connection  with  respiration  and  phonation. 

Glottis  (Figs.  194-196,  199-201).— This  opening  differs  in 
shape  under  different  conditions.  Its  length  from  the  angle  of  the 
true  vocal  cords  in  front  to  the  vocal  processes  of  the  arytenoid 
cartilages  behind  is  about  2.5  cm.,  and  its  breadth  when  dilated 
varies  from  0.8  cm.  to  1.2  cm.  During  ordinary  inspiration  its 
breadth  increases,  becoming  triangular,  and  in  very  deep  or  forced 


FIG.  199. — The  voicing  (female)  larynx:  A,  small  or  highest  register;  B,  upper 
thin  or  middle  register;  (7,  lower  thin  or  middle  register;  T,  T,  tongue;  F,  F,  false 
vocal  cords ;  8,  S,  cartilages  of  Santorini ;  W,  W,  cartilages  of  Wrisberg ;  V,  V,  vocal 
cords  (after  Browne  and  Behnke). 

inspiration  lozenge-shaped,  while  during  phonation  the  vocal  cords 
are  more  approximated  than  at  the  end  of  respiration. 


FIG.  200.— The  larynx  in  gentle 
breathing:  L,  epiglottis  ;F,  vocal  cords; 
8,  cartilages  of  Santorini,  which  sur- 
mount the  arytenoid  cartilages ;  P,  P, 
ventricular  bands  (Lennox- Browne). 


FIG.  201.— The  larynx  in  deep  breath- 
ing: WP,  tracheal  rings;  B,  openings 
of  bronchi ;  P,  P,  ventricular  bands 
(Lennox-Browne) . 


The  changes  which  take  place  during  voice-production  are  more 
fully  considered  in  connection  with  that  function  of  the  larynx 
(p.  389). 

True  Vocal  Cords. — These  are  called  also  vocal  bands  and  vocal 
ligaments.  They  consist  of  strong  fibrous  bands  covered  with 
mucous  membrane,  and  parallel  with  them  and  attached  to  them 
are  the  inner  portions  of  the  thyro-arytenoid  muscles. 

The  mucous  membrane  lines  the  entire  larynx,  and  forms  the 
folds  already  described.  Below  the  false  vocal  cords  it  is  covered 
with  columnar  ciliated  epithelium.  Above  these  cords  cilia  are  only 
found  in  front  up  to  the  middle  of  the  epiglottis.  Elsewhere,  in- 
cluding the  true  cords,  the  epithelium  is  stratified. 

Vessels  and  Nerves.— The  arteries  which  supply  the  larynx 
are  derived  from  the  superior  and  inferior  thyroid.  The  nerves  are 


THE  TRACHEA.  361 

the  superior  laryngeal,  a  branch  of  the  vagus,  which  supplies  the 
mucous  membrane,  the  cricothyroid  and  arytenoid  muscles;  and 
the  inferior  laryngeal,  or  recurrent  laryngeal,  also  a  branch  of  the 
vagus,  which  supplies  all  the  other  muscles,  and  also  the  arytenoid 
muscle. 

THE   TRACHEA. 

The  trachea  or  windpipe  (Fig.  202)  is  about  11  cm.  in  length, 
and  2.5  cm.  in  diameter,  and  extends  from  the  cricoid  cartilage  to 
its  division  into  the  bronchi,  which  corresponds  to  the  fourth  or 
fifth  dorsal  vertebra. 

Structure. — It  is  composed  of  rings  of  cartilage,  from  16  to 
20  in  number,  which  are  incomplete  behind,  where  the  trachea  is 
in  contact  with  the  esophagus.  These  cartilaginous  rings  are  situ- 


^"Xr'W- 
"  •"•&,;  :>v: 


o 

FIG.  202. — From  longitudinal  section  of  human  trachea,  stained  in  orcein  (Huber). 

ated  within  the  two  layers  of  an  elastic  fibrous  membrane.  In 
the  spaces  between  the  rings  these  layers  unite,  thus  forming 
a  single  membrane.  The  membrane  behind  is  also  single.  Be- 
tween the  ends  of  the  cartilaginous  rings  is  also  a  transverse  layer 
of  unstriped  muscular  tissue,  trachealis  muscle,  and  posterior  to 
this  are  some  longitudinal  fibers  of  the  same  kind.  The  trachea 
is  lined  with  mucous  membrane  covered  with  columnar  ciliated 
epithelium,  and  in  it  are  mucous  glands,  tracheal  glands,  whose 
secretion  lubricates  the  membrane,  and  there  are  elastic  fibers 
arranged  longitudinally. 

Blood-vessels. — The  artery  supplying  the  trachea  is  the 
inferior  thyroid,  and  its  veins  terminate  in  the  thyroid  venous  plexus. 

Nerves. — The  nerves  are  branches  of  the  vagus  and  sympa- 
thetic. % 


362  RESPIRATION. 

THE  BRONCHI. 

These  are  two  in  number  :  the  right  bronchus,  which  is  more 
horizontal  than  the  left  and  is  about  2.5  cm.  in  length,  divides 
into  three  subdivisions  which  go  to  the  right  lung,  which  has  three 
lobes.  The  left  bronchus  is  about  5  cm.  long,  and  divides  into 
two  branches,  one  for  the  upper,  and  the  other  for  the  lower  lobe 
of  the  left  lung.  The  bronchi  are,  like  the  trachea,  made  up  of 
cartilaginous  rings  or  plates  with  intervening  membrane. 

THE  LUNGS. 

There  are  two  lungs,  right  and  left,  situated  in  corresponding 
sides  of  the  thorax ;  each  being  divided  by  fissures  into  lobes — 
the  right  into  three,  superior,  middle,. and  inferior,  and  the  left 
into  two,  superior  and  inferior.  The  root  of  the  lung,  where  this 
organ  is  connected  with  the  heart  and  trachea,  is  composed  of 
bronchus,  pulmonary  artery,  pulmonary  veins,  bronchial  arteries, 
bronchial  veins,  pulmonary  plexus  of  nerves,  lymphatics,  bronchial 
glands,  and  areolar  tissue,  all  covered  by  a  serous  membrane — 
the  pleura. 

Structure. — Each  lung  is  covered  by  the  visceral  layer  of  the 
pleura,  beneath  which  is  areolar  tissue  containing  elastic  fibers. 
This  coat  exists  not  only  on  the  outside,  but  also  penetrates  into 
the  interior  between  the  lobules.  The  lobules  form  the  parenchyma 
of  the  lung. 

Lobules. — A  lobule  consists  of  a  terminal  or  ultimate  bronchial 
tube  and  the  air-cells  or  alveoli,  into  which  it  opens,  together  with 
such  pulmonary  and  bronchial  vessels,  lymphatics,  and  nerves  as 
are  associated  therewith.  Each  lobule  may  be  regarded  as  a 
miniature  lung,  a  lobe  being  made  up  of  many  lobules.  Their 
form  and  size  vary,  those  which  are  on  the  exterior  of  the  lung 
being  pyramidal  in  shape,  the  base  forming  a  polygonal  figure ; 
while  those  more  deeply  seated  present  considerable  variations  from 
this. 

To  obtain  a  clearer  idea  of  the  minute  structure  of  the  lung  than 
can  be  obtained  from  the  above  description,  it  will  be  profitable 
to  approach  the  lobule  from  the  direction  of  the  bronchi. 

After  entering  the  lung  the  bronchi  divide  and  subdivide  into 
two  branches,  or  dichotomously,  occasionally  into  three.  The 
cartilages  become  plates  or  lamince,  between  them  being  mem- 
brane. When  the  bronchial  tubes  become  as  small  as  0.5  mm. 
the  cartilage  disappears  and  the  walls  are  membranous ;  the  fibrous 
tissue  and  the  longitudinal  elastic  fibers  continue  throughout,  while 
the  muscular  tissue,  equally  extensive,  is  arranged  around  the 
tubes.  The  mucous  membrane  continues  to  be  covered  with 
ciliated  epithelium  of  the  columnar  variety,  until  the  lobule  is 
reached.  At  this  point  each  subdivision  of  a  bronchus  becomes 


PLATE  III. 


A,  upper  bone  of  sternum;  B,  B,  two  first  ribs  ;  <7,  (7,  second  pair  of  ribs  ;  D,  D, 
right  and  left  lungs;  E,  lower  end  of  sternum;  F,  F,  right  and  left  halves  of  the 
diaphragm  in  sections:  the  right  half  separating  the  right  lung  from  the  liver,  the 
left  half  separating  the  left  lung  from  the  broad  cardiac  end  of  the  stomach ;  G,  G, 
eighth  pair  of  ribs;  K,  K,  ninth  pair  of  ribs  (Maclise). 


THE  LUNGS. 


363 


a  tabular  bronchial  tube  or  bronchiole  or  ultimate  bronchial  tube, 
and  on  one  side  dilatations  exist,  air-cells  or  pulmonary  alveoli. 


Respiratory 
bronchiole. 


Alveolar  duct.— 


—  Artery. 


—  Lung- tissue. 


Bronchiole. 


Fio.  203. 


—  Lung-tissue. 


FIG.  204. 

FIGS.  203  and  204.— Two  sections  of  cat's  lung:    Fig.  203,  X  52;  Fig.  204,  X  35 
(Bohm  and  Davidoff). 

These  increase  in  number,  and,  although  at  first  limited  to  one  side 
of  each  bronchiole,  they  subsequently  surround  the  tube,  and  the 


364  RESPIRATION. 

bronchiole  becomes  enlarged,  forming  the  atrium,  which  opens 
into  sac-like  cavities,  infundibula,  each  infundibulum  being  about 
1  mm.  in  diameter,  and  these  open  into  air-cells  or  pulmonary 
alveoli,  which  latter  have  a  diameter  of  from  0.1  mm.  to  0.3  mm. 

At  the  infundibula  the  muscular  tissue  is  less  abundant  and 
the  elastic  fibers  are  arranged  around  the  openings  of  the  air-cells. 
The  epithelium  in  the  bronchioles  is  both  columnar  ciliated  and 
cubical  non-ciliated  ;  but  in  the  infundibula  and  alveoli  it  is  of  the 
pavement  variety,  with  some  cubical. 

Blood-vessels. — Branches  of  the  pulmonary  artery  pass  into 
the  lung  with  the  bronchial  tubes  and  terminate  in  the  pulmonary 
capillaries  (Fig.  205),  which  as  plexuses  lie  under  the  mucous  mem- 
brane of  the  walls  of  the  infundibula  and  alveoli  and  of  the  par- 
titions or  septa  between  them.  The  capillaries  have  very  thin 


Blood-capillaries 
seen  in  surface 


""  Alveolus  in  cross- 
section. 


FIG.  205.— Section  through  injected  lung  of  rabbit  (Bohm  and  Davidoff). 

walls  and  a  diameter  of  about  8  p,  while  the  spaces  between  them 
are  even  smaller.  Small  veins  collect  the  blood,  and  these  uni- 
ting with  others  finally  discharge  into  the  pulmonary  veins,  which 
bring  the  blood  back  to  the  left  auricle.  Some  of  the  blood  brought 
to  the  lungs  by  the  bronchial  arteries  returns  to  the  venous  circula- 
tion through  these  veins. 

The  bronchial  arteries,  branches  of  the  aorta,  supply  the  blood 
necessary  to  nourish  the  lung  tissue,  and  the  bronchial  veins  carry 
most  of  it  back  to  the  venous  circulation,  by  the  way  of  the  vena 
azygos  major  on  the  right  side,  and  by  the  superior  intercostal  or 
left  azygos  vein  on  the  left  side. 

Nerves. — The  innervation  of  the  lungs  is  supplied  through 
the  pulmonary  plexuses  from  the  sympathetic  and  vagus.  The 
nerves  accompany  the  bronchial  tubes. 


THE  THORAX.  365 

THE  PLEURA, 

The  pleura  is  a  serous  membrane  which  covers  the  lung,  pleura 
pulmonalis  or  serous  layer  of  the  pleura,  being  at  its  root  reflected 
so  as  to  line  the  thorax,  forming  the  pleura  costalis  or  parietal  layer 
of  the  pleura.  The  theoretical  space  between  the  two  layers  is 
the  pleural  cavity.  Inasmuch  as  these  layers  are  normally  always 
in  contact,  there  is  no  actual  space  or  cavity  between  them, 
although  they  are  moistened  by  a  small  amount  of  secretion  for 
lubricating  purposes.  When  fluid  collects  here,  as  it  does  in  some 
forms  of  pleuritis  or  inflammation  of  the  pleura,  the  layers  are 
then  separated. 

Blood-vessels. — The  arteries  which  supply  the  pleura  have 
their  origin  in  the  intercostal,  internal  mammary,  musculophrenic, 
thymic,  pericardiac,  and  bronchial  arteries.  The  veins  are  similar 
in  their  anatomic  relations. 

Nerves. — The  nerves  are  of  phrenic  and  sympathetic  origin, 
and  accompany  the  branches  of  the  bronchial  artery. 

THE  THORAX. 

The  thorax  or  chest  is  the  structure  which  contains  the  lungs, 
heart,  and  great  blood-vessels.  The  thoracic  cavity  is  the 
space  within  the  thorax  in  which  these  organs  are  located.  The 
thorax  is  formed  by  the  vertebral  column  and  the  ribs  posteriorly, 
the  sternum  and  the  costal  cartilages  anteriorly,  and  by  the  ribs 
laterally.  The  spaces  between  the  ribs,  intercostal  spaces,  are  filled 
by  the  intercostal  muscles.  These  muscles  and  others  which  are 
attached  to  the  thorax  are  concerned  in  the  movements  of  respira- 
tion. 

Vertebral  Column. — This  portion  of  the  thorax  is  rigid  and 
takes  no  part  in  any  of  the  movements  connected  with  respiration. 
The  vertebrae  which  are  concerned  in  the  formation  of  the  thorax 
are  the  12  dorsal  (Figs.  206,  207),  and  the  anatomic  points  of 
interest  are  the  facets  and  demifacets  on  their  bodies,  which  form 
articulating  surfaces  for  the  heads  of  the  ribs,  and  the  facets  on  the 
transverse  processes  for  articulation  with  the  tubercles  of  the  ribs. 
Between  the  vertebrae  are  intervertebral  disks  of  fibrocartilage, 
which  under  the  microscope  present  the  appearance  of  fibrous 
tissue  with  articular  cartilage  (Fig.  31,  page  39). 

Ribs. — All  the  ribs,  from  the  first  to  the  twelfth,  enter  into 
the  formation  of  the  thorax,  and  articulate  posteriorly  with  the 
vertebrae. 

The  first  seven,  the  true  ribs,  are  attached  anteriorly  to  the  ster- 
num, not  directly,  but  by  means  of  the  costal  cartilages ;  while  of  the 
others,  the  false  ribs,  3,  the  eighth,  ninth,  and  tenth,  are  attached 
to  the  cartilage  of  the  seventh  rib,  and,  2,  the  eleventh  and 
twelfth,  the  floating  ribs$  are  free  at  their  anterior  extremities. 


366 


RESPIRATION. 


The  ribs  differ  very  materially  in  their  general  relations ;  thus  the 
upper  ones  are  less  oblique  than  the  lower  ones,  the  obliquity  in- 


FIG.  206. — a,  Vertebral  column;  b,  clavicle;  d,  ribs;  e,  sternum. 

creasing  as  far  down  as  the  ninth  rib,  when  it  becomes  less  (Fig.  206). 


Axis  of 
rotation. 


FIG.  207.— First  dorsal  vertebra  and  rib.      FIG.  208.— Sixth  dorsal  vertebra  and  rib. 

Costal  Cartilages.— These  are  characterized  by  their  elas- 
ticity, which  is  greater  in  early  life,  and  in  the  false  ribs  than  in 


THE  THORAX.  367 

the  true.  The  elasticity  diminishes  as  years  go  on,  until,  at  an 
advanced  age,  they  are  calcified.  Rib-cartilage  is  not  infrequently 
fibrous  in  character,  and  the  cells  are,  as  a  rule,  larger  and  collected 
into  groups  of  greater  size  than  those  of  articular  cartilage  (Fig. 
209). 

Respiratory  Muscles. — The  muscles  which  are  concerned 
in  the  respiratory  movements  of  the  thorax  may  be  divided  into 
three  groups:  (1)  Of  ordinary  inspiration;  (2)  of  forced  inspira- 


Matrix.  — ir^t: 


» 

— ™     ' 

il 


FIG.  209. — Hyaline  cartilage  (costal  cartilage  of  the  ox).  Alcohol  preparation ; 
X  300.  The  cells  are  seen  inclosed  in  their  capsules.  In  the  figure  a  are  repre- 
sented frequent  but  by  no  means  characteristic  radiate  structures  (Bohm  and 
Davidoff). 

tion;  (3)  of  forced  expiration.  There  are  no  muscles  concerned 
in  ordinary  expiration. 

Muscles  of  Ordinary  Inspiration. — These  are  diaphragm,  scaleni, 
external  intercostals,  internal  intercostals  (anterior  portion),  leva- 
tores  costarum. 

Th.e  Diaphragm. — This  forms  the  lower  boundary  of  the 
thoracic  cavity,  separating  it  from  that  of  the  abdomen.  It  arises 
from  the  whole  interior  surface  of  the  thorax,  and  the  fibers 
which  compose  its  muscular  portion  are  inserted  into  the  central 
or  cordiform  tendon.  Through  the  diaphragm  pass  the  vena  cava, 
the  esophagus,  and  the  aorta. 

Nerve-supply. — The  phrenic  nerves  and  the  phrenic  plexus 
of  the  sympathetic. 

Scaleni. — The  scalenus  anticus  is  a  muscle  which  arises  from 
the  anterior  tubercles  of  the  transverse  processes  of  the  third, 
fourth,  fifth,  and  sixth  cervical  vertebrae,  and  is  inserted  into  the 


368  RESPIRATION. 

first  rib.  The  scalenus  medius  arises  from  the  posterior  tuber- 
cles of  the  transverse  processes  of  the  cervical  vertebrae  from  the 
second  to  the  seventh,  both  inclusive,  and  is  also  inserted  into  the 
first  rib.  The  scalenus  posticus  arises  from  the  posterior  tuber- 
cles of  the  transverse  processes  of  the  fifth,  sixth,  and  seventh 
cervical  vertebrae,  and  is  inserted  into  the  second  rib. 

Nerve-supply. — Branches  of  the  anterior  divisions  of  the  fifth, 
sixth,  seventh,  and  eighth  cervical  nerves.  The  scalenus  medius 
receives  an  additional  supply  from  the  deep  external  branches  of 
the  cervical  plexus. 

Intercostal  Muscles. — These  fill  up  the  intercostal  spaces,  and 
consist  of  muscular  and  tendinous  fibers,  the  combination  of  the 
two  kinds  of  tissue  giving  both  contractility  and  strength.  There 
are  two  sets  of  these  muscles,  external  and  internal. 

External  Intercostal  Muscles. — These  fill  the  intercostal  spaces 
from  the  tubercles  of  the  ribs  to  the  costal  cartilages,  from  which 
point  to  the  sternum  there  is  no  muscular  tissue.  They  arise  from 
the  lower  borders  of  the  ribs,  and  are  inserted  into  the  upper 
borders  of  the  ribs  below  them.  The  direction  of  their  fibers  is 
obliquely  downward  and  forward. 

Nerve-supply. — The  intercostal  nerves. 

Internal  Intercostals. — Those  Avhich  are  attached  to  the  true 
ribs  extend 'from  the  sternum  to  the  angles  of  the  ribs,  where  the 
muscular  tissue  ceases  to  exist  and  a  membranous  structure  takes 
its  place  as  far  as  the  vertebrae.  Those  which  are  attached  to  the 
false  ribs  extend  from  their  cartilages  backward  in  a  manner 
similar  to  that  just  described.  The  fibers  of  this  group  arise  from 
the  ridge  on  the  inner  surface  of  the  ribs  and  from  the  costal 
cartilages,  and  are  inserted  into  the  upper  borders  of  the  ribs 
below.  The  direction  is  obliquely  downward  and  forward,  the 
external  and  internal  intercostals,  therefore,  cross  each  other. 

Nerve-supply. — The  intercostal  nerves. 

Levatores  Costarum. — These  muscles  arise  from  the  extremities 
of  the  transverse  processes  of  the  vertebrae  from  the  seventh 
cervical  to  the  eleventh  dorsal,  and  are  inserted  into  the  upper 
borders  of  the  ribs  between  the  tubercles  and  the  angle. 

Nerve-supply. — The  intercostal  nerves. 

Action. — The  first  rib  on  each  side  is  raised  and  held  in  a  fixed 
position  by  the  scaleni  muscles ;  the  external  intercostals  now 
contracting,  all  the  ribs  are  raised.  This  elevation  of  the  ribs  is 
assisted  by  the  contraction  of  that  portion  of  the  internal  inter- 
costals which  is  situated  in  the  front  of  the  thorax,  and  by  that  of 
the  levatores  costarum.  These  are,  therefore,  all  muscles  of  ordi- 
nary inspiration. 

All  authorities  are  not  agreed  as  to  the  action  of  the  inter- 
costals. Haller  regarded  both  external  and  internal  intercostals 
as  muscles  of  inspiration  ;  Keen  considers  the  external  intercostals 


THE  THORAX.  369 

as  being  depressors  of  the  ribs,  hence  muscles  of  expiration  ;  while 
the  function  of  the  internal  set  he  considers  to  be  that  of  elevating 
the  ribs,  and  therefore  regards  them  as  muscles  of  inspiration. 

The  form  of  the  diaphragm,  when  its  muscular  tissue  is  re- 
laxed, is  that  of  a  dome  with  its  convexity  upward.  When  the 
muscular  fibers  contract  they  pull  down  the  central  tendon,  and  at 
the  same  time  become  themselves  less  convex  and  straighter.  This 
movement  constitutes  the  descent  of  the  diaphragm,  and  results  in 
increasing  the  capacity  of  the  thorax ;  therefore  the  diaphragm  is 
a  muscle  of  inspiration — indeed,  it  is  the  most  important  of  all  the 
inspiratory  muscles. 

The  abdominal  cavity  contains  the  abdominal  organs — liver, 
stomach,  spleen,  intestines,  etc. — and  in  its  descent  the  diaphragm 
depresses  these  structures,  which  under  the  pressure  yield  to  a  cer- 
tain extent,  the  protrusion  of  the  abdominal  walls  aiding  by 
allowing  this  displacement  to  take  place  to  a  greater  degree  than 
it  would  were  they  rigid.  There  is,  however,  a  limit  to  the 
amount  that  the  central  tendon  can  descend,  and  when  this  limit 
is  reached  the  tendon  becomes  a  fixed  point  from  which  the  mus- 
cular tissue  can  act,  and  the  effect  is  to  raise  the  lower  ribs  to 
which  it  is  attached ;  thus  the  capacity  of  the  thorax  is  still  more 
increased.  This  descent  amounts  to  from  5.5  mm.  to  11.5  mm.  in 
quiet  breathing  and  42  during  forced  inspiration.  Not  only  are 
the  abdominal  organs  depressed,  but  they  are  also  compressed,  and 
their  attachments  put  upon  the  stretch ;  when,  therefore,  the  mus- 
cular tissue  of  the  diaphragm  ceases  its  contraction  and  begins  to 
relax,  the  elasticity  of  the  depressed  and  compressed  abdominal 
contents  and  the  abdominal  walls  tends  to  raise  the  diaphragm 
into  the  position  it  occupied  at  the  beginning  of  the  respiratory 
act.  This  ascent  of  the  diaphragm  is,  therefore,  a  phenomenon 
of  expiration. 

Muscles  of  Forced  Inspiration. — Trapezius,  latissimus  dorsi, 
rhomboideus  minor,  rhomboideus  major,  serratus  posticus  superior, 
serratus  posticus  inferior,  iliocostalis,  quadratus  lumborum,  sterno- 
mastoid,  pectoralis  major,  pectoralis  minor,  subclavius. 

Trapezius. — This  muscle  arises  from  the  superior  curved  line 
of  the  occipital  bone,  the  ligamentum  nuchse,  spinous  process  of 
seventh  cervical,  and  the  spinous  processes  of  all  the  dorsal 
vertebrae,  and  the  supraspinous  ligament,  and  is  inserted  into 
the  clavicle,  acromion  process,  and  spine  of  the  scapula. 

Nerve-supply. — The  muscular  branch  of  the  spinal  accessory 
and  branches  from  the  anterior  divisions  of  the  third  and  fourth 
cervical  nerves. 

Latissimus  Dorsi. — It  arises  from  the  spinous  processes  of  the 
six  lower  dorsal  and  those  of  the  lumbar  and  sacral  vertebrae,  the 
supraspinous  ligament,  crest  of  the  ilium,  and  3  or  4  lower  ribs, 
and  is  inserted  into  the  bicipital  groove  of  the  humerus. 

24 


370  RESPIRATION. 

Nerve-supply. — Middle  or  long  subscapular  nerve. 

Rhomboideus  Minor. — It  arises  from  the  ligamentum  nuchae 
and  spinous  processes  of  the  seventh  cervical  and  first  dorsal 
vertebrae,  and  is  inserted  into  the  scapula  at  the  root  of  the  spine. 

Nerve-supply. — The  anterior  division  of  the  fifth  cervical 
nerve.  , 

Rhomboideus  Major. — This  arises  from  the  spinotis  processes 
of  the  4  or  5  upper  dorsal  vertebrae  and  the  supraspinous  ligament, 
and  is  inserted  into  the  tendinous  arch  extending  from  the  scapula 
at  the  root  of  its  spine  to  its  inferior  angle. 

Nerve-supply. — The  anterior  division  of  the  fifth  cervical  nerve. 

Serratus  Posticus  Superior. — This  muscle  arises  from  the  liga- 
mentum nuchae  and  the  spinous  processes  of  the  seventh  cervical 
and  2  or  3  upper  dorsal  vertebrae  and  the  supraspinous  ligament, 
and  is  inserted  into  the  second,  third,  fourth,  and  fifth  ribs  beyond 
their  angles. 

Nerve-supply. — The  external  branches  of  the  posterior  divisions 
of  the  upper  dorsal  nerve. 

Serratus  Posticus  Inferior. — It  arises  from  the  spinous  processes 
of  the  eleventh  and  twelfth  dorsal  and  the  2  or  3  upper  lumbar 
vertebrae  and  supraspinous  ligament,  and  is  inserted  into  the  four 
lower  ribs  beyond  their  angles. 

Nerve-supply. — The  external  branches  of  the  posterior  division 
of  the  lower  dorsal  nerves. 

lliocostalis. — This  is  sometimes  called  sacrolumbalis.  It  is  the 
outer  part  of  the  erector  spinae  which  arises  from  the  sacro-iliae 
groove,  and  forms  a  broad  tendon  attached  to  the  sacrum,  lumbar 
vertebrae,  supraspinous  ligament,  and  that  of  the  ilium  and  the 
sacrum.  It  is  inserted  into  the  angles  of  the  6  or  7  lower  ribs. 

Nerve-supply  comes  through  the  external  branches  of  the  pos- 
terior divisions  of  the  lumbar  and  dorsal  nerves. 

Quadratus  iMmborum. — It  arises  from  the  iliolumbar  ligament 
and  the  crest  of  the  ilium,  and  is  inserted  into  the  last  rib  and 
the  transverse  processes  of  the  4  upper  lumbar  vertebrae. 

Nerve-supply. — The  anterior  branches  of  the  lumbar  nerves. 

Sternomastoid. — It  arises  from  the  sternum  and  clavicle,  and 
is  inserted  into  the  mastoid  process  of  the  temporal  bone  and  the 
occipital  bone. 

Nervous  Supply. — The  spinal  accessory  and  deep  branches  of 
the  cervical  plexus. 

Pectoralis  Major. — It  arises  from  the  clavicle,  sternum,  carti- 
lage of  the  true  ribs,  aponeurosis  of  the  obliquus  externus,  and  is 
inserted  into  the  anterior  bicipital  ridge  of  the  humerus. 

Nervous  Supply. — The  anterior  thoracic  nerve. 

Pectoralis  Minor. — It  arises  from  the  third,  fourth,  and  fifth 
ribs,  and  from  the  aponeurosis  covering  the  intercostal  muscles, 
and  is  inserted  into  the  coracoid  process  of  the  scapula. 


THE  THORAX  371 

Nervous  Supply. — The  anterior  thoracic  nerves. 

Subclavius. — It  arises  from  the  first  rib  and  its  cartilage,  and  is 
inserted  into  the  clavicle. 

Nervous  Supply. — A  filament  from  the  cord  formed  by  the 
union  of  the  fifth  and  sixth  nerves.  * 

-  Serratus  Magnus. — It  arises  from  the  8  upper  ribs  and  the 
aponeurosis  covering  the  intercostal  muscles,  and  is  inserted  into 
the  scapula. 

Nervous  Supply. — The  posterior  thoracic  nerve. 

Action. — The  trapezius  and  rhomboidei  fix  the  scapula,  and 
the  serratus  magnus,  contracting,  raises  the  ribs.  The  arm  being 
fixed,  the  latissimus  dorsi  also  raises  the  ribs.  The  ribs  are  like- 
wise elevated  by  the  action  of  the  serratus  posticus  superior,  while 
the  serratus  posticus  inferior  draws  downward  and  backward  the 
lower  ribs,  increasing  thereby  the  capacity  of  the  thorax.  Some 
authorities  regard  the  serratus  posticus  superior  as  being  brought 
into  action  in  ordinary  respiration.  When  the  ribs  are  drawn 
downward  they  are  held  there  by  the  serratus  posticus  inferior, 
thus  overcoming  the  upward  lifting  of  the  ribs  by  the  diaphragm. 
The  iliocostalis  and  quadratus  lumborum  fix  the  last  rib  and  oppose 
the  tendency  of  the  diaphragm  to  raise  it.  The  head  being  fixed, 
the  sternomastoid  elevates  the  thorax.  The  group  of  muscles 
consisting  of  the  pectoralis  major  and  minor  and  the  subclavius 
draw  the  ribs  upward  when  the  head  is  fixed. 

In  this  manner  all  the  muscles  mentioned,  some  to  a  greater 
and  some  to  a  lesser  degree,  aid  in  the  process  of  forced  inspira- 
tion. 

Muscles  of  Forced  Expiration. — Internal  intercostals,  triangularis 
sterni,  obliquus  externus,  obliquus  internus,  transversalis,  rectus. 

Internal  Intercostals  (p.  368). 

Triangularis  Sterni. — This  muscle  is  situated  on  the  back  of 
the  sternum  and  anterior  portion  of  the  ribs.  It  arises  from  the 
sternum,  ensiform  cartilage,  and  costal  cartilages  of  the  3  or  4 
lower  true  ribs,  and  is  usually  inserted  into  the  costal  cartilages 
of  the  second,  third,  fourth,  and  fifth  ribs. 

Nerve-supply. — The  intercostal  nerves. 

Obliquus  Externus. — This  muscle  is  more  familiarly  known  as 
the  external  oblique.  It  arises  from  the  8  lower  ribs,  and  is  inserted 
into  the  crest  of  the  ilium  and  into  tendinous  fibers  which  form  a 
broad  aponeurosis. 

Nerve-supply. — The  lower  intercostal  nerves. 

Obliquus  Internus. — This  is  also  called  the  internal  oblique.  It 
arises  from  Poupart's  ligament,  the  crest  of  the  ilium,  and  the 
posterior  lamella  of  the  lumbar  fascia,  and  is  inserted  into  the  os 
pubis,  linea  alba,  through  an  aponeurosis  to  the  cartilages  of  the 
seventh,  eighth,  and  ninth  ribs,  and  into  the  cartilages  of  the  tenth, 
eleventh,  and  twelfth  ribs. 


372  RESPIRATION. 

Nerve-supply. — The  lower  intercostal  nerves  and  the  ilio- 
inguinal  nerve. 

Transversalis. — It  arises  from  Poupart's  ligament,  the  crest  of 
the  ilium,  cartilages  of  the  6  lower  ribs,  and  transverse  processes 
of  the  lumbar  vertebrae,  and  is  inserted  into  the  linea  alba  or 
pubes. 

Nerve-supply. — The  lower  intercostal  nerves. 

Rectus  Abdominis. — It  arises  from  the  os  pubis,  and  is  inserted 
into  the  cartilages  of  the  fifth,  sixth,  and  seventh  ribs. 

Nerve-*supply. — The  lower  intercostal  nerves. 

Action. — The  internal  intercostal  muscles,  except  the  anterior 
portion  (p.  368),  depress  the  ribs,  at  the  same  time  inverting  their 
lower  borders,  thus  diminishing  the  size  of  the  thoracic  cavity. 

The  triangularis  sterni  draws  down  the  costal  cartilages,  thus 
aiding  in  the  expelling  of  air  from  the  lungs. 

When  the  pelvis  and  the  spine  are  fixed,  the  external  and  in- 
ternal oblique,  trans versalis,  and  the  rectus  compress  the  thorax 
at  its  lower  part,  and  thus  assist  in  the  expiratory  process. 

RESPIRATORY  MOVEMENTS, 

The  respiratory  movements  are  of  two  kinds — inspiratory  and 
expiratory. 

Inspiratory  Movements.— By  virtue  of  the  inspiratory 
movements  the  air  passes  into  the  lungs.  During  their  perform- 
ance the  thorax  expands  under  the  influence  of  the  diaphragm 
and  the  inspiratory  muscles  (p.  367).  In  inspiration  all  the  diam- 
eters of  the  chest  are  increased.  The  descent  of  the  diaphragm 
increases  the  vertical  diameter  (Plate  1).  At  the  same  time  the 
transverse  and  anteroposterior  diameters  are  also  increased.  The 
shape  and  direction  of  the  ribs  are  such  that  when  they  are  raised 
their  convexities  are  carried  outward,  and  thus  the  transverse 
diameter  of  the  thorax  is  increased.  But  this  movement  also  carries 
the  sternum  forward,  thereby  increasing  the  anteroposterior  diam- 
eter. Under  some  circumstances,  as  when  there  is  some  obstruc- 
tion to  the  entrance  of  air,  additional  muscles,  called  extraordinary 
muscles  of  inspiration  or  muscles  of  forced  inspiration  (p.  369),  are 
brought  into  action.  In  this  way  most  of  the  muscles  about  the 
thorax  may  be  called  upon.  It  should  be  noted  that  inspiration 
is  an  active  process — that  is,  one  that  requires  for  its  performance 
the  action  of  muscles. 

Expiratory  movements  are  for  the  most  part  passive  in 
their  nature — that  is,  are  not  due  to  muscular  contraction.  During 
the  descent  of  the  diaphragm,  referred  to  in  describing  the  inspi- 
ratory movements,  the  elastic  abdominal  organs  and  their  attach- 
ments and  the  abdominal  walls  are  put  upon  the  stretch.  At  the 
end  of  the  inspiratory  act  the  diaphragm  ceases  to  contract,  and 


RESPIRATORY  MOVEMENTS. 


373 


by  virtue  of  the  elasticity  of  these  structures  the  contents  of  the 
abdomen  return  to  the  position  they  occupied  at  the  beginning  of 
the  diaphragm's  descent,  and  in  so  doing  this  structure  is  carried 
back  to  its  original  position.  The  elevation  of  the  ribs  by  the 
contraction  of  the  external  intercostals  during  inspiration  twists 
the  elastic  costal  cartilages  which  join  the  ribs  to  the  sternum  :  as 
soon  as  these  muscles  cease  to  contract  these  cartilages  untwist, 
and  in  so  doing  aid  in  the  return  of  the  ribs.  In  describing  the 
structure  of  the  lungs  it  was  stated  that  the  walls  of  the  lobules 
are  rich  in  elastic  tissue :  in  inspiration  these  lobules  are  greatly 
distended,  their  walls  being  put  on  the  stretch.  When  the  inspira- 
tory  forces  cease  to  act,  then  this  tissue,  by  virtue  of  its  elasticity, 
returns  to  its  former  condition,  and  in  so  doing  expels  the  air, 
constituting  expiration.  Contractility  may  be  said  to  be  the 
inspiratory  force  ;  elasticity,  the  expiratory  force. 

As  in  inspiration,  so  in  expiration,  there  are  occasions  when 
obstruction  to  the  outgoing  air  exists,  and  forced  expiration  be- 
comes necessary.  The  muscles  concerned  in  this  act*  are  known 


FIG.  210.— The  larynx  in  gentle 
breathing :  L,  epiglottis ;  V,  vocal  cords ; 
8,  cartilages  of  Santorini,  which  sur- 
mount the  arytenoid  cartilages  ;  P,  P, 
ventricular  bands  (Lennox-Browne). 


FIG.  211.— The  larynx  in  deep  breath- 
ing :  W,  P,  tracheal  rings ;  B,  openings 
of  bronchi ;  P,  P,  ventricular  bands 
(Lennox-Browne) . 


as  extraordinary  muscles  of  expiration  or  muscles  of  forced  expira- 
tion, whose  arrangement  is  such  that  in  their  contraction  the 
capacity  of  the  thorax  is  diminished.  They  have  been  already 
described  (p.  371).  The  abdominal  walls,  by  exerting  pressure 
on  the  abdominal  viscera,  and  thus  on  the  diaphragm,  still  further 
diminish  the  thoracic  cavity  and  force  out  the  contained  air. 

Movements  of  the  Glottis. — There  are  in  connection 
with  the  process  of  respiration  certain  movements  of  the  glottis 
which  are  important.  On  examination  of  the  interior  of  the 
larynx  it  will  be  seen  that  during  inspiration  the  vocal  cords 
separate,  and  during  expiration  approach  each  other.  During 
deep  breathing  (Fig.  211)  the  separation  of  the  cords  is  greater 
than  in  quiet  breathing  (Figs.  210,  219). 

The  area  of  the  trachea  is  nearly  three  times  that  of  the  space 
between  the  cords  at  the  beginning  of  inspiration.  The  separation 
of  these  cords  is  effected  by  the  contraction  of  the  posterior  crico- 
arytenoid  muscles,  which,  by  their  attachment  to  the  arytenoid 
cartilages,  rotate  these  outward,  and  thus  separate  the  posterior 


374  RESPIRATION. 

ends  of  the  cords  which  are  attached  to  them,  increasing  the  area 
nearly  twofold.  When  these  muscles  cease  their  contraction,  as 
they  do  at  the  end  of  the  inspiratory  act,  then  the  elasticity  of  the 
cartilages  brings  the  muscles  back  to  the  position  they  occupied  at 
the  beginning  of  inspiration.  These  movements  of  the  glottis 
occur  synchronously  with  the  respiratory  movements  of  the  thorax. 
The  muscles  of  the  larynx  have  already  been  described  (p.  355). 

CAPACITY  OF  THE  LUNGS, 

At  the  beginning  of  an  ordinary  inspiration  the  lungs  contain 
air,  which  so  distends  them  that  the  visceral  layer  of  the  pleura 
is  in  contact  with  the  parietal  layer.  As  the  thorax  enlarges  the 
air  in  the  lungs  distends  them  still  more,  so  that  they  are  still 
kept  in  contact  with  the  thoracic  walls.  This  contact  between  the 
visceral  and  parietal  layers  of  the  pleura  is  constant,  irrespective 
of  the  amount  of  distention  of  the  lungs.  The  expansion  of  the 
air  in  the  lungs  makes  it  of  less  density  than  the  external  air 
with  which  it  is  in  communication  through  the  air-passages,  and 
immediately  there  is  a  flow  of  external  air  into  these  passages 
to  establish  an  equilibrium :  this  inflow  constitutes  inspiration. 
Immediately  following  air  is  expelled  from  the  lungs,  and  this 
outflow  constitutes  expiration.  To  this  volume  of  air  which  flows 
in  and  out  during  ordinary  respiration  the  name  of  tidal  air  is 
given,  from  the  resemblance  which  the  process  bears  to  the  flow 
and  ebb  of  the  tide.  The  amount  of  this  tidal  air  is  variously 
stated  by  different  authorities;  some  place  it  as  low  as  49  c.c., 
and  others  as  high  as  1640  c.c.  It  varies  greatly  in  different 
individuals,  and  in  the  same  individual  according  to  the  manner 
and  frequency  of  his  breathing.  Hutchinson  has  made  80  deter- 
minations on  different  individuals,  and  obtained  from  114  c.c.  to 
196  c.c.  in  a  condition  of  rest,  and  from  262  c.c.  to  360  c.c. 
during  exercise.  One  observation  was  as  high  as  1262  c.c.  In 
newborn  children  it  is  35  c.c. 

Each  individual  has  the  power,  however,  of  taking  into  the 
lungs  an  additional  amount  of  air  over  and  above  the  tidal  air,  by 
a  deep  or  forced  inspiration.  To  this  additional  amount  the  term 
complemental  air  is  applied,  and  it  may  be  regarded  as  averaging 
about  1500  c.c. 

As  more  air  is  taken  in  by  forced  inspiration  than  is  usually 
inhaled  during  an  ordinary  inspiration,  so  by  a  forced  expiration 
more  air  is  expelled  than  is  ordinarily  exhaled  during  an  ordinary 
expiration.  To  the  air  thus  expelled  during  a  forced  expiration 
the  name  of  reserve  or  supplemental  air  is  given.  Hutchinson  states 
the  amount  to  vary  from  1148  c.c.  to  1804  c.c.,  while  by  some  it 
has  been  placed  at  2624  c.c. 

But  even  after  all  the  air  has  been  expelled  that  can  be  by 


TYPES  OF  RESPIRATION.  375 

bringing  into  play  all  the  muscles  and  other  forces  available,  there 
still  remains  a  volume  of  air  which  cannot  be  forced  out ;  this  is 
the  residual  air,  and  has  been  estimated  by  Sir  Humphrey  Davy  to 
be  674  c.c.  It  has  been  measured  by  different  observers  upon 
both  the  living  and  the  dead  body.  In  one  set  of  observations 
upon  9  corpses,  the  minimum  was  640  c.c.,  the  maximum,  1231 
c.c.,  the  mean,  981  c.c.  In  another  series  of  observations  on  living 
males  the  results  were  440  c.c.  minimum,  1250  c.c.  maximum, 
and  796  c.c.  mean ;  and  in  still  another  upon  living  females,  347 
c.c.  minimum,  526  maximum,  and  478  c.c.  mean.  Neupauer 
determined  the  amount  of  residual  air  in  a  living  subject  to  be 
very  much  greater. 

Vital  capacity  is  the  volume  of  air  over  which  an  individual 
can  exert  control.  It  is  the  amount  which  he  can  expel  by  a 
forced  expiration  after  having  taken  a  forced  inspiration ;  it  is, 
therefore,  the  sum  of  the  tidal,  complemented,  and  supplemental 
air ;  it  excludes  the  residual  air.  Hutchinson  gives  it  as  3558  c.c., 
basing  his  estimate  on  1923  observations. 

The  vital  capacity  of  the  newborn  child  is  about  120  c.c. 

Although  it  is  impossible  to  give  any  figures  which  will  repre- 
sent measurements  that  are  necessarily  so  variable  as  those  just 
given,  still  it  may  be  of  use  to  have  an  approximate  estimate  for 
purposes  of  reference ;  and  we  may  place  the  amount  of  tidal  air 
at  300  c.c.,  complemental  air  at  1500  c.c.,  reserve  air  at  1500  c.c., 
and  residual  air  at  1000  c.c. 

Frequency  of  Respiration. — In  the  newborn  child  the 
number  of  respirations  per  minute  is  44  ;  at  five  years  of  age,  26  ;  at 
twenty  years,  20  ;  at  thirty  years,  1 6  ;  and  at  fifty  years,  18.  These 
figures  represent  an  average  during  a  quiescent  condition.  Should 
the  respirations  be  counted  during  sleep,  they  would  be  1  or  2  less 
per  minute  ;  during  great  activity  they  would  be  increased  con- 
siderably, in  the  adult  running  up  to  30  or  more. 

TYPES  OF  RESPIRATION. 

It  has  been  the  practice  among  writers  on  physiology  to  speak 
of  the  superior  costal  or  female  type  of  respiration  and  the 
abdominal,  inferior  costal,  or  male  type.  The  following  condensed 
statement  from  one  of  the  best  text-books  on  this  subject  represents 
the  views  of  these  writers  :  "  In  children,  as  well  as  in  the  adult 
male,  under  ordinary  conditions,  the  diaphragm  performs  most 
of  the  work,  and  the  movements  of  the  abdomen  are  the  only 
ones  especially  noticeable  ....  In  the  female  the  movements 
of  the  chest,  particularly  of  its  upper  half,  are  habitually  more 
prominent  than  those  of  the  abdomen,  and  this  difference  in  the 
mechanism  of  respiration  is  characteristic  of  the  sexes."  The 
protrusion  of  the  abdominal  wall,  caused  by  the  descent  of  the 


376  RESPIRATION. 

diaphragm,  is  very  marked  in  children,  and  produces  the  ab- 
dominal type  of  respiration.  The  costal  type  spoken  of  above 
as  characteristic  of  the  female  was  supposed  to  be  a  wise  provision 
of  nature,  in  order  that  when  pregnancy  should  occur  the  respira- 
tory movements  would  not  be  interfered  with,  as  they  would  be 
did  the  female  possess  the  inferior  costal  type  of  respiration  seen 
in  the  male. 

Very  careful  and  complete  studies  of  women  in  and  out  of 
civilization,  the  lower  portions  of  whose  chests  have  never  been 
compressed  with  corsets  or  with  other  devices  calculated  to  pre- 
vent expansion  of  these  parts,  have  demonstrated  that  the  supposed 
respiratory  difference  in  male  and  female  does  not  exist  naturally, 
and  that  when  it  is  found  it  is  due  to  the  corset,  and  not  to  any 
peculiarity  of  sex.  Indeed,  if  the  male  chest  is  encased  in  a 
corset,  the  inferior  costal  type  becomes  changed  at  once  into  the 
superior  costal.  It  is  also  of  interest  to  note  that  in  one  case  at 
least  the  observation  was  made  in  which  the  inferior  costal  type 
of  respiration  was  well  marked  in  a  pregnant  woman  within  one 
week  of  her  confinement. 

CHEMISTRY  OF  RESPIRATION. 

The  air,  when  dry  and  measured  at  0°  C.  and  760  mm.  press- 
ure, contains  20.96  parts  by  volume  of  oxygen,  79.02  parts  of 
nitrogen,  and  0.03  part  of  carbon  dioxid.  About  1  per  cent,  of 
what  is  given  as  nitrogen  is  argon.  Watery  vapor  is  also  present, 
the  amount  varying  under  different  circumstances,  being  greater 
the  higher  the  temperature  of  the  air.  The  term  absolute  humidity 
has  reference  to  the  total  amount  of  watery  vapor  which  a 
volume  of  air  contains,  irrespective  of  the  question  of  tem- 
perature ;  the  term  relative  humidity  is  used  to  express  the  pro- 
portion of  watery  vapor  present  in  the  air  at  certain  temperatures 
as  compared  with  air  fully  saturated,  saturation  being  expressed 
by  100.  Absolute  humidity  is  expressed  in  grams  per  cubic 
meter  or  in  grains  per  cubic  foot,  while  relative  humidity  is 
expressed  in  percentages.  Thus  if  the  temperature  of  the  air 
is  4°  C.,  and  it  is  saturated  with  watery  vapor,  its  relative  humidity 
would  be  said  to  be  100;  if,  now,  its  temperature  was  raised  to 
27°  C.  its  relative  humidity  would  be  only  24,  because  the  higher 
the  temperature  the  more  vapor  can  a  given  volume  of  air  contain, 
and  the  air  at  27°  C.  would  hold  a  much  greater  amount  than 
when  its  temperature  was  4°  C. 

The  amount  of  moisture  present  in  air  is  an  important  factor 
in  the  preservation  of  health.  If  it  is  too  dry,  the  air-passages 
are  irritated ;  while  if  too  moist,  there  is  produced  a  feeling  of 
oppression.  A  relative  humidity  of  70  is,  as  a  rule,  very  agree- 
able. Traces  of  ammonia,  some  ozone,  and  sodium  chlorid  are 


CHEMISTRY  OF  RESPIRATION.  377 

also  found  in  the  atmospheric  air.  Besides  these  constituents, 
which  are  universal,  there  are  many  others  that  may  or  may  not 
be  present  as  the  result  of  processes  of  manufacture. 

Expired  Air. — When  the  atmospheric  air  has  been  breathed  its 
composition  is  markedly  changed  in  the  following  particulars :  1. 
It  has  gained  carbon  dioxid,  the  amount  being  increased  from  0.03 
or  0.04  part  per  cent,  to  4.38.  2.  It  has  lost  oxygen,  the  20.96 
volumes  per  cent,  being  reduced  to  16.03,  or  about  5  per  cent.  It 
should  be  noted  that  the  loss  of  oxygen  is  greater  than  can  be 
accounted  for  by  the  amount  of  that  gas  returned  in  the  carbon 
dioxid,  the  difference  representing  the  amount  used  up  in  processes 
of  oxidation  constantly  going  on  in  the  body.  3.  It  has  gained 
watery  vapor,  the  expired  air  being  saturated.  The  actual  amount 
of  vapor  which  it  receives  while  in  the  lungs  will,  of  course,  vary. 
If  the  air  when  inspired  is  cool  and  dry,  it  will  absorb  more 
moisture  from  the  body  than  if  it  is  moist  and  warm.  The  daily 
loss  from  this  source  is  about  540  grams.  4.  The  expired  air  is, 
as  a  rule,  warmer  than  the  inspired.  Thus  in  a  series  of  obser- 
vations it  was  found  that  when  the  inspired  air  had  a  temperature 
of  from  15°  to  20°  C.,  when  expired  its  temperature  was  37.3° 
C. ;  when  the  inspired  air  was  —6.3°  C.,  it  was  29.80°  C.  when 
expired;  and  when  41.9°  C.  at  inspiration,  it  was  38.1°  C.  at 
expiration.  The  inspired  air  is  warmed  from  1  to  2  degrees  more 
when  taken  in  by  the  nose  than  by  the  mouth.  5.  The  actual 
volume  of  expired  as  compared  with  inspired  air  is  less  by  about 
2  per  cent.  6.  The  expired  air  contains  certain  volatile  organic 
matters,  whose  presence  is  at  once  recognized  by  the  sense  of  smell, 
among  them  crowd-poison,  although  chemists  have  not  yet  made 
us  acquainted  with  their  exact  composition. 

The  following  table  represents  the  average  composition  and 
temperature  of  inspired  and  expired  air : 

Inspired  Air.  Expired  Air. 

Oxygen 20.96  16.03 

Nitrogen 78.00  78.00 

Argon          1.00  1.00 

Carbon  dioxid 0.04  4.38 

Watery  vapor variable  saturated 

Temperature '. "  about  37°  C. 

Respiratory  Quotient. — This  is  a  term  employed  to  express  the 
ratio  between  the  carbon  dioxid  given  off  and  the  oxygen  ab- 
sorbed, and  is  obtained  by  dividing  the  former  by  the  latter — i.  e., 
CO  4.34 
O  4  93    =  0-88,  so  *^at  there  is  gained  0.88  volume  of  CO2  for 

every  volume  of  O  absorbed.     This  ratio  is  an  exceedingly  vari- 
able one,  differing  in  different  animals,  and  even  in  the  same  indi- 
vidual with  age,  food,  temperature  of  the  air,  during  exercise,  etc. 
There  are  various  reasons  which  account  for  these  differences. 


378  RESPIRATION. 

It  is  to  be  borne  in  mind,  in  the  first  place,  that  the  sources  of 
carbon  dioxid  in  the  animal  body  are  numerous.  The  oxygen 
which  is  absorbed  at  any  given  time  does  not  immediately  appear 
in  the  carbon  dioxid  given  off ;  it  may  be  absorbed  and  enter  into 
combinations,  which  may  retain  it  for  a  considerable  time  ;  so  that 
at  any  given  time  the  amount  of  oxygen  absorbed  may  be 
greater  than  that  given  off  in  the  carbon  dioxid,  or  vice  versa. 

Then,  too,  more  CO2  is  formed  in  proportion  to  the  amount  of 
oxygen  absorbed  by  the  decomposition  of  some  substances  than 
others.  Thus  when  carbohydrates  constitute  the  diet  the  amount 
of  oxygen  which  they  contain  is  enough  to  satisfy  their  hydrogen, 
but  fats  and  proteids  need  more,  and  in  the  formation  of  water 
they  use  up  oxygen  ;  from  this  it  follows  that  more  oxygen  is 
absorbed  during  an  animal  than  during  a  vegetable  diet.  When 
the  amount  of  carbon  dioxid  given  off  equals  the  amount  of  oxygen 
absorbed,  the  respiratory  quotient  is  1.  The  quotient  will  be  higher 
in  herbivora,  where  it  is  from  0.9  to  1.0,  than  in  carnivora,  where 
it  is  from  0.75  to  0.8.  It  is  interesting  to  note  that  when  an  her- 
bivorous animal  is  fasting — that  is,  at  a  time  when  it  is  taking  in 
no  food,  but  is  living  on  its  own  tissues,  and  is  therefore  for  the 
time  being  a  carnivorous  animal — the  quotient  is  that  of  the  car- 
nivora, 0.75. 

In  observations  upon  man  it  is  found  that  before  feeding  the 
quotient  is  0.84  to  0.89  ;  when  meat  or  fat  is  given,  0.76 ;  with 
potatoes,  0.93  ;  and  with  glucose,  1.03. 

The  respiratory  quotient  is  higher  in  adults  than  in  children ; 
during  the  day  than  at  night ;  during  wakefulness  than  during 
sleep  ;  during  activity  than  during  rest. 

Ventilation.- — It  is  manifest  that  if  at  each  inspiration 
oxygen  is  extracted  from  the  air,  in  the  course  of  time  the  amount 
of  this  gas  will  be  so  reduced  as  to  make  its  want  seriously  felt. 
It  is  necessary,  therefore,  in  order  to  keep  the  amount  of  oxygen 
up  to  the  standard,  that  some  provision  should  be  made  to  supply 
it.  Besides  the  removal  of  the  oxygen,  the  air  is  still  further 
rendered  unsuited  for  respiratory  purposes  by  the  carbon  dioxid, 
and  especially  by  the  organic  matter  thrown  off  by  the  expired 
air  ;  the  oxygen  being  still  further  diminished  by  stoves  and  lights, 
and  the  air  being  vitiated  by  the  products  of  combustion.  Another 
and  no  less  important  source  of  vitiation  of  the  air  is  the  organic 
matter  thrown  off  from  the  skin,  particularly  in  those  of  uncleanly 
habits.  Decayed  teeth  and  foul  mouths  add  to  the  contamination. 
To  supply  oxygen  and  to  remove  these  impurities  are  the  objects 
of  ventilation. 

A  common  test  to  determine  whether  the  air  of  an  enclosed  space 
contains  sufficient  oxygen  for  respiratory  purposes  is  to  see  if  a 
candle  will  burn  in  it.  This  test  is  used  to  determine  whether  the 
air  in  vaults  or  in  excavations  is  fit  for  respiration.  A  candle  will 
not  burn  if  the  air  contains  only  17  volumes  per  cent,  of  oxygen ; 


CHEMISTRY  OF  RESPIRATION.  379 

a  man  can  breathe  without  difficulty  if  there  are  but  15  volumes  per 
cent.  So  far,  then,  as  the  question  of  oxygen  is  concerned,  a  man 
could  breathe  where  a  candle  would  not -burn,  but  it  does  not 
necessarily  follow  that  it  is  always  safe  for  a  man  to  venture  where 
a  candle  will  burn,  for  sometimes,  although  there  may  be  oxygen 
sufficient  to  sustain  life,  poisonous  gases  may  also  be  present  in  an 
amount  sufficient  to  produce  a  fatal  result.  It  would  be  a  surer 
test  to  place  a  dog  in  the  suspected  place  and  leave  him  there  for 
twenty  minutes.  If  it  survives,  it  will  be  safe  for  a  man  to  enter. 

It  is  a  matter  of  common  experience  that  injury  to  health 
follows  confinement  in  badly  ventilated  apartments,  but  the  cause 
thereof  has  never  been  satisfactorily  determined.  The  generally 
accepted  theory  is  that  it  is  not  due  to  the  carbon  dioxid  which  is 
given  oif  by  the  lungs,  but  to  the  organic  matter — crowd-poison — 
exhaled  in  the  expired  air  and  also  given  off  from  the  surface  of 
the  body,  especially  of  those  who  are  not  cleanly  in  their  habits, 
and  who  resort  to  bathing  the  body  too  infrequently.  Those  who 
maintain  these  views  state  that  an  air  which  contains  respiratory 
CO2 — i.  e.j  CO2  produced  by  respiration — to  the  amount  of  more 
than  0.07  per  cent,  is  unwholesome  air  to  breathe,  and  yet  that 
CO2  may  be  present  to  the  extent  of  2  per  cent,  provided  that  its 
presence  is  due  to  'chemical  processes,  as  in  soda-water  factories, 
and  may  be  breathed  without  inconvenience  or  any  injurious  conse- 
quences resulting.  Indeed,  so  reliable  observers  as  Brown^S^quacd 
and  (PArsony^l  have  breathed  air  in  which  CO2  was  present  to  the 
amount  of  20  per  cent,  for  two  hours  without  marked  distress. 
When,  therefore,  injurious  effects  follow  from  breathing  air  con- 
taining 0.8  per  cent,  of  CO2,  which  represents  that  present  in  a 
very  badly  ventilated  lecture-hall,  it  must  be  due  to  something 
else  than  the  CO2,  and  they  attribute  it  to  the  organic  matter 
already  referred  to.  Brown^Se^iiard  and  d'Arsonval,  who  believed 
that  it  was  the  organic  matter  from  the  lungs  wKTch  was  the  poison- 
ous matter,  injected  into  rabbits  the  condensed  vapor  of  the  ex- 
pired air  with  fatal  results. 

On  the  other  side  of  the  question  are  those  who  maintain  that 
the  injurious  consequences  of  breathing  vitiated  air  are  due  to  the 
excessive  amount  of  CO2  and  the  deficiency  of  oxygen,  and  not  to 
organic  matter.  In  support  of  this  theory  we  have  the  following 
observations  :  Haldane  and  Lorraine  Smith  found  that  in  breathing 
air  containing  18.6  per  cent,  of  CO2,  within  a  minute  or  two  they 
suffered  from  hyperpnea,  distress,  flushing,  cyanosis,  and  mental 
confusion ;  and  the  injections  of  condensed  vapor-breath  into 
rabbits,  practised  by  Brown-Sequard  and  df Arson val,  have  been 
repeated  by  several  experimenters  with  negative  results.  Besides 
these,  other  experiments  have  been  performed,  showing  that  no 
volatile  poisons  are  exhaled  with  the  expired  air.  Among  recent 
investigations  on  this  subject  are  those  of  Haldane  and  Lorraine 
Smith.  From  these  they  conclude  as  follows  : 


380  RESPIRATION. 

"  1.  The  immediate  dangers  from  breathing  air  highly  vitiated 
by  respiration  arise  entirely  from  the  excess  of  carbon  dioxid  and 
deficiency  of  oxygen,  .and  not  from  any  special  poison. 

"  2.  The  hyperpnea  is  due  to  excess  of  carbon  dioxid,  and  is  not 
appreciably  affected  by  the  corresponding  deficiency  of  oxygen. 
The  hyperpnea  begins  to  appear  when  the  carbon  dioxid  rises  to 
from  3  to  4  per  cent.  At  about  10  per  cent,  there  is  extreme 
distress. 

"  3.  Excess  of  carbon  dioxid  is  likewise  the  cause,  or  at  least 
one  cause,  of  the  frontal  headache  produced  by  highly  vitiated 
air. 

"  4.  Hyperpnea  from  defect  of  oxygen  begins  to  be  appreciable 
when  the  oxygen  in  the  air  breathed  has  fallen  to  a  point  which 
seems  to  differ  in  different  individuals.  In  one  case  the  hyperp- 
nea became  appreciable  at  about  12  per  cent.,  and  excessive  at 
about  6  per  cent." 

Haldane  and  Smith  also  regard  the  odorous  substances  present 
in  rooms  due  to  a  want  of  cleanliness  as  contributing  to  the  dis- 
comfort caused  by  breathing  the  air  of  such  rooms. 

It  must  be  remembered  that  the  oxygen  of  the  air  is  consumed 
and  carbon  dioxid  and  other  impurities  produced  by  stoves,  gas- 
burners,  and  lamps,  as  well  as  by  respiration.  Thus  a  large  gas- 
burner  will  in  one  hour  consume  as  much  oxygen  as  a  human 
being  will  in  five  hours,  and  at  the  same  time  will  be  produced 
carbon  dioxid  and  monoxid,  sulphur  compounds,  and  other  gaseous 
impurities,  all  of  which  vitiate  the  air  to  a  considerable  degree. 
At  the  same  time  the  air  is  heated.  Perhaps  one  of  the  most 
important  advantages  which  has  accrued  from  the  introduction  of  • 
electricity  as  applied  to  illuminating-purposes  is  the  entire  absence 
of  heat  and  of  those  impurities  which  so  impoverish  the  air  of 
inhabited  rooms. 

It  is  generally  conceded  that  if  the  respiratory  CO2  in  the  air 
does  not  exceed  0.02  per  cent,  above  that  which  is  ordinarily 
present  in  all  air— 0.03  or  0.04  per  cent.— bringing  it  up  to  0.06 
or  0.07  per  cent.,  no  harm  will  result,  and  adequate  ventilation 
will  be  secured — i.  e.,  keeping  the  CO2  from  increasing  beyond 
0.06  or  0.07  per  cent.  To  bring  this  about  will  require  as  a 
minimum  60,000  liters  (2000  cubic  feet)  per  hour  per  individual, 
but  this  should  be  increased  by  at  least  one^half  (making  it  3000 
cubic  feet)  to  provide  for  the  increased  production  of  CO2  caused 
by  active  exercise ;  and  in  factories  and  workshops  where  all  the 
operatives  are  men,  and  all  actively  at  work,  this  amount  often 
needs  to  be  as  much  as  6000  cubic  feet.  For  hospitals,  where  the 
emanations  from  the  sick  are  more  likely  to  vitiate  the  air  than 
are  those  from  the  well,  at  least  6000  cubic  feet  should  be  pro- 
vided. These  figures  take  no  account  of  gas-burners  or  lamps, 
and  for  these  there  should  be  allowed  not  less  than  1800  cubic 


CHEMISTRY  OF  RESPIRATION.  381 

feet  of  air  for  each  cubic  foot  of  gas  consumed,  and  18,000  cubic 
feet  for  each  pound  of  oil  burned. 

The  cubic  space  allotted  to  each  individual  must  also  be  taken 
into  account,  for  experience  has  proved  that  unless  the  ventilating 
arrangements  are  very  perfect,  the  air  of  an  inhabited  room  can- 
not be  changed  oftener  than  three  times  an  hour  without  causing 
draughts,  which  are  uncomfortable,  and  it  may  be  dangerous  to 
health.  It  becomes  necessary,  therefore,  to  provide  at  least  1000 
cubic  feet  of  air-space  per  individual.  In  the  dormitories  of 
workhouses  the  amount  allowed  does  not  often  exceed  300  cubic 
feet ;  in  military  barracks,  600  cubic  feet,  and  in  hospitals,  1 200 
cubic  feet. 

It  has  also  been  found  by  practical  experience  that  in  rooms 
that  have  a  height  of  more  than  12  feet  the  conditions  are  not 
favorable  for  proper  ventilation,  for  the  reason  that  organic  matters 
have  a  tendency  to  remain  in  the  lower  parts  of  rooms.  A  room 
50  feet  high,  with  20  square  feet  of  floor-space,  would  give  1000 
cubic  feet  of  air-space,  but  it  would  not  be  the  same  from  a  sani- 
tary point  of  view  as  a  room  10  feet  in  all  its  dimensions.  Atten- 
tion must,  therefore,  be  paid  to  the  amount  of  floor-space  allotted 
to  each  individual ;  this  varies  according  to  circumstances.  It 
should  be  at  least  100  square  feet.  Of  course,  where  rooms  are 
occupied  for  but  a  short  time,  as  in  theaters,  churches,  etc.,  where 
after  the  audiences  are  dismissed  the  buildings  can  be  thoroughly 
aired  by  the  admission  of  external  air,  all  these  restrictions  do  not 
apply. 

It  seems  hardly  necessary  to  say  that  due  attention  must  be 
paid  to  the  source  from  which  the  introduced  air  is  drawn.  If  it 
is  obtained  from  filthy  cellars  or  from  dirty  streets,  it  may  be  as 
impure  as  that  which  it  is  designed  to  replace. 

For  any  further  discussion  of  this  subject  our  readers  are  re- 
ferred to  text-books  on  liygiene. 

Changes  in  the  Blood  due  to  Respiration. — When  the 
blood  reaches  the  lungs  from  the  heart  it  is  venous,  and  when  it 
leaves  the  lungs  to  return  to  the  heart  it  is  arterial.  The  con- 
version, then,  of  the  venous  blood  into  arterial  takes  place 
while  it  is  traversing  the  pulmonary  capillaries.  In  its  passage 
the  bluish-red  color  which  characterizes  venous  blood  becomes 
changed  to  the  scarlet  color  of  arterial  blood,  and  at  the  same 
time  the  venous  blood  gives  up  a  portion  of  its  CO2  to  the  air, 
and  takes  O  from  it.  From  100  volumes  of  blood,  whether 
arterial  or  venous,  approximately  60  volumes  of  both  gases  can 
be  obtained ;  the  proportion,  however,  varying.  Thus  in  human 
arterial  blood  there  is  O,  21.6;  CO2,  40.3;  and  N,  16.  The 
amount  of  nitrogen  is  practically  the  same  in  both  varieties  of 
blood.  It  is  impossible  to  give  figures  which  represent  accurately 
the  composition  of  venous  blood,  for  while  analyses  of  arterial 


382  RESPIRATION. 

blood  taken  from  the  different  arteries  vary  but  little,  those 
of  venous  blood  from  different  parts  of  the  venous  system  vary  to 
a  considerable  degree;  and  even  the  blood  from  the  same  vein 
will  have  a  different  composition  at  different  times,  as,  for  instance, 
that  coming  from  a  gland  when  active  or  at  rest.  In  general, 
venous  blood  may  be  said  to  contain  O  from  8  to  12  per  cent.,  and 
CO2  about  46  per  cent.  Zuntz  has  made  many  analyses,  and 
concludes,  as  a  result,  that  venous  blood,  as  compared  with  arterial, 
contains  7.15  volumes  per  cent,  less  of  O,  and  8.2  volumes  per 
cent,  of  CO2. 

Although  arterial  blood  contains  but  21.6  per  cent,  of  O,  still 
it  can  be  made  to  take  up  as  much  as  23  per  cent.,  which  would 
about  saturate  it.  But  even  the  2]  .6  per  cent,  is  more  than  is 
needed  by  the  tissues  in  their  metabolic  processes.  Unless,  there- 
fore, the  blood  contains  less  oxygen  than  normal,  there  is  no  advan- 
tage to  be  derived  from  inhaling  oxygen  gas.  If,  however,  the 
venous  condition  is  marked,  then  oxygen  inhaled  under  pressure 
may  do  good.  While  the  arterial  blood  is  nearly  saturated  with 
oxygen,  experiments  have  shown  that  it  can  take  up  nearly  four 
times  as  much  CO2  as  it  ordinarily  contains. 

Causes  of  the  Interchange  between  O  and  CO2  in  the 
I/ungfS.  —  The  trachea  and  bronchi  can  contain  about  140  c.c.  of 
air,  so  that  at  each  inspiration,  when  300  c.c.  or  more  of  tidal  air 
are  taken  in,  the  difference  between  these  two  figures,  160  c.c.  or 
more,  must  represent  the  amount  which  passes  at  each  inspiration 
into  the  alveoli  of  the  lungs.  When  expiration  occurs  an  equal 
volume  is  exhaled;  thus  by  the  repeated  alternation  of  inspiration 
and  expiration  the  air  in  the  lungs  is  being  constantly  changed. 

But  the  most  potent  factor  in  bringing  about  this  interchange  is 
the  diffusion  of  the  gases,  which  depends  upon  their  partial  pressure 
—  L  e.,  the  part  of  the  total  pressure  of  the  air  which  is  exerted  by 
each  of  its  different  components.  This  is  also  spoken  of  as  tension 
by  some  writers  ;  although  others  use  the  term  partial  pressure  with 
reference  to  gases  in  a  mechanical  mixture,  as  in  atmospheric  air  ; 
and  that  of  tension  with  reference  to  gases  in  solution,  meaning 
thereby  "the  pressure  required  to  keep  the  gas  in  solution."  If 
we  regard  760  mm.  of  mercury  as  representing  the  pressure  of 
the  atmosphere,  and  20.96  as  the  percentage  of  the  total  volume 

20.96  X  760 
represented  by  oxygen,  then  -  -  will  equal  the  pressure 


exerted  by  the  oxygen,  or  its  partial  pressure  or  tension,  which 
is  159.29  mm.  The  partial  pressure  of  the  CO2  =  ~]~00~ 

0.30  mm.  If  now  we  ascertain  the  partial  pressure  of  these  gases 
in  the  alveoli,  we  shall  have  the  principal  conditions  affecting  their 
diffusion.  The  partial  pressure  of  O  in  the  alveoli  is  estimated 
at  about  114  mm.  and  of  C09  at  36  mm.  The  O  then  in  the  air 


CHEMISTRY  OF  RESPIRATION.  383 

as  it  enters  the  respiratory  passages  has  a  partial  pressure  of  159.29 
mm.,  while  in  the  alveoli  it  is  only  122  mm. ;  therefore  it  will  diffuse 
inward  until  it  reaches  the  point  of  lowest  pressure.  On  the  other 
hand,  the  partial  pressure  of  CO2  is  greatest  in  the  alveoli — 38  mm. 
as  compared  with  0.30  mm. ;  this  gas  will  therefore  diffuse  outward. 

There  is  a  third  force  causing  diffusion  which  is  regarded  as 
possessing  different  value  by  different  authorities ;  this  is  the 
cardiopneumatic  movements.  Each  time  the  heart  contracts  it 
becomes  smaller,  and  the  pressure  within  the  thorax,  but  outside 
the  lungs — the  intrathoracic  pressure — is  diminished,  with  the  re- 
sult of  causing  the  lungs  to  expand  slightly,  and  air  consequently 
to  enter  them.  When  diastole  occurs  and  the  volume  of  the  heart 
becomes  larger,  the  intrathoracic  pressure  is  relatively  increased, 
and  the  air  is  forced  out  of  the  lungs.  Besides,  therefore,  the  en- 
trance and  exit  of  air  due  to  the  inspiratory  and  expiratory  move- 
ments, there  is  a  corresponding  movement  of  the  air  due  to  the 
contraction  and  dilatation  of  the  ventricles. 

Causes  of  the  Interchange  of  O  and  CO2  between  the 
Air  and  the  Blood.— The  fact  that  the  amount  of  O  and  CO2 
in  the  blood  does  not  follow  the  general  law  that  the  amount  of 
gas  which  a  liquid  absorbs  depends  to  a  great  extent  upon  its 
pressure,  is  conclusive  proof  that  these  gases  are  not  to  any  great 
extent  in  solution  in  the  blood.  O  is  in  solution  in  the  plasma, 
but  to  the  extent  of  less  than  one  volume,  and  in  venous  blood 
only  about  5  per  cent,  of  the  CO2  present  is  in  solution.  Inas- 
much as  the  amount  of  both  of  these  gases  is  greatly  in  excess  of 
these  figures,  we  must  look  for  some  other  explanation  of  their 
presence  in  the  blood  in  the  quantities  in  which  they  there  exist 
than  to  solution. 

When  the  gases  are  extracted  from  the  blood,  as  they  may  be 
by  the  use  of  a  pump  devised  for  this  purpose  (Fig.  212),  the 
oxygen  which  is  in  solution  is  given  off  gradually  as  the  pressure 
is  reduced,  but  it  is  not  until  the  pressure  has  been  reduced  to 
from  one-thirtieth  to  one-tenth  of  an  atmosphere  that  most  of  it 
comes  off,  and  this  it  does  suddenly  when  this  low  pressure  is 
reached.  From  this  it  is  evident  that  most  of  the  oxygen  is  in 
chemical  combination,  and  this  pressure  at  which  the  gas  is  given 
off  is  the  tension  of  dissociation.  From  various  observations  and 
experiments  we  know  that  the  combination  is  one  between  oxygen 
and  hemoglobin,  forming  oxyhemoglobin.  It  has  been  ascertained 
that  theoretically  oxyhemoglobin  can  contain  23.38  volumes  per 
cent,  of  O,  although  it  never  does,  but  only  about  20  per  cent., 
because  the  hemoglobin  is  not  saturated ;  still,  blood  from  which 
the  red  corpuscles  and  consequently  the  hemoglobin  have  been  re- 
moved, as  in  plasma  or  serum,  can  take  up  only  0.26  volume  per 
cent.  The  tension  of  O  in  arterial  blood  is  29.64  mm.  of  mercury, 
and  in  venous  blood  22.04  mm. 


384 


RESPIRATION. 


The  tension  of  CO2  in  the  blood  is  as  follows :  In  arterial 
blood  21.28  mm.,  and  in  venous  blood  41.04  mm.  CO2  exists  in 
venous  blood  in  solution  to  the  amount  of  about  5  per  cent.;  in 
loose  chemical  combination,  75  to  85  per  cent.;  and  in  firm  chemi- 
cal combination,  10  to  20  per  cent. — or  about  45  volume  per  cent, 
in  all.  The  CO2  is  in  solution  in  the  plasma,  in  combination  with 
globulin  and  alkali,  and  with  sodium  in  the  form  of  carbonates 
and  bicarbonates.  About  one-third  of  the  carbon  dioxid  of  the 


FIG.  212.— Kemp's  gas  pump.     (For  detailed  description  see  American  Text-BooTc  of 
Physiology,  vol.  i.,  p.  420.) 

blood  exists  in  the  blood-corpuscles,  both  white  and  red,  but  prin- 
cipally in  the  latter,  where  it  is  in  combination  with  the  alkaline 
phosphates,  with  globulin  and  hemoglobin. 

We  have  seen  that  by  various  forces  the  oxygen  in  the  outside 
air  reaches  the  alveoli,  while  in  turn  the  carbon  dioxid  in  the 
latter  situation  reaches  the  exterior  ;  we  have  now  to  consider  how 
the  interchange  between  the  CO2  in  the  blood  and  the  O  in  the 
alveoli  is  effected.  We  have  learned  that  the  tension  of  the  O 


CHEMISTRY  OF  RESPIRATION.  385 

in  the  alveolar  air  is  about  114  mm.,  although  one  observer  at 
least  places  it  as  low  as  99  mm.  This  has  never  been  accurately  de- 
termined. The  tension  of  CO2  in  the  alveolar  air  is  about  36  mm. 
In  order  to  ascertain  why  the  O  of  the  air  goes  to  the  blood  and 
the  CO2  of  the  blood  to  the  air,  we  must  first  know  the  tension 
of  O  and  CO2  in  the  blood.  For  this  purpose  an  instrument 
known  as  an  aerotonometer  is  used.  The  principle  underlying 
this  instrument  is  thus  described  by  Pembrey  in  Schafer's  Physi- 
ology :  "  Blood  in  contact  with  a  mixture  of  oxygen,  nitrogen,  and 
carbon  dioxid  gives  up  some  of  its  gases  if  their  partial  pressures 
are  greater  than  those  of  the  corresponding  gases  in  the  mixture  ; 
on  the  other  hand,  if  the  tensions  of  the  gases  in  the  blood  be 
lower  than  the  respective  tensions  of  the  gases  in  the  mixture,  the 
blood  takes  up  gas.  These  interchanges  persist  until  equilibrium 
is  established,  until  the  tension  or  partial  pressure  of  the  gas  in 
the  blood  is  equal  to  that  of  the  corresponding  gas  in  the  mixture. 
In  the  aerotonometer  the  blood  is  made  to  pass  in  a  thin  layer 
through  a  glass  tube  or  tubes  containing  mixtures  of  gases 
of  known  quantity  and  tension,  and  it  is  arranged  by  prac- 
tice that  the  tension  of  the  gases  shall  in  the  one  case  be  greater, 
in  the  other  case  smaller,  than  the  tensions  of  the  corresponding 
gases  in  the  blood.  The  gases  in  these  tubes,  after  the  blood  has 
passed  through  them,  are  analyzed,  and  from  the  alteration  in  the 
proportion  in  the  two  tubes  it  is  possible  to  calculate  the  partial 
pressure  of  the  gases  in  the  blood.  The  aerotonometer  is  sur- 
rounded by  a  water-jacket  with  a  temperature  of  39°  C." 

Another  aerotonometer  is  that  of  Fredericq,  and  Bohr  has 
devised  one  known  as  an  hemato-aerometer. 

The  results  obtained  by  these  different  instruments  vary  con- 
siderably. Strassburg  gives  the  tension  of  CO2  in  venous  blood 
of  the  right  side  of  a  dog's  heart  as  5.4  per  cent,  of  an  atmosphere  ; 
and  2.2  to  3.8  per  cent,  in  arterial  blood.  Herter  gives  the  ten- 
sion of  O  in  arterial  blood  as  10  per  cent,  of  an  atmosphere. 
Bohr  has  obtained  quite  different  results  :  101  to  104  mm.  of 
mercury  for  the  tension  of  O  in  arterial  blood — higher  than  that 
of  the  air  in  the  trachea.  He  also  found  that  when  the  dog,  the 
subject  of  the  experiment,  breathed  pure  air,  the  tension  of  the 
CO2  in  arterial  blood  rises  from  nothing  to  28  mm.  of  mercury, 
and  when  the  dog  breathed  air  containing  CO2  the  tension  varied 
between  0.9  and  57.8  mm.  That  is  to  say,  the  tension  of  CO2 
was  greater  in  the  tracheal  air  than  in  the  blood.  If  this  is  so, 
it  is  manifest  that  the  passage  of  the  CO2  of  the  blood  outward 
to  the  air  could  not  be  due  to  diffusion  ;  so  that  to  explain  the 
actual  facts  Bohr  concludes  that  the  tissues  of  the  lungs  play 
an  active  part  in  the  absorption  of  oxygen  and  the  elimination  of 
carbon  dioxid.  Haldane  and  Lorraine  Smith  have  substituted  for 
the  aerotonometer  a  method  by  which  "  the  tension  of  O  in  the 

25 


386  RESPIRATION. 

arterial  blood  is  calculated  from  the  percentage  of  carbon  monoxid 
breathed  by  the  subject  of  the  experiment,  and  from  the  final 
saturation  of  his  blood  with  carbon  monoxid  "  (Pembrey).  Their 
results  are  26.2  per  cent,  of  an  atmosphere,  or  200  rum.  of  mercury, 
about  twice  that  of  oxygen  in  the  alveoli,  which  would  confirm 
Bohr's  views  that  diffusion  cannot  account  for  the  absorption  of 
oxygen  by  the  blood  while  flowing  through  the  pulmonary  cap- 
illaries, but  that  it  is  to  be  attributed  to  the  epithelial  cells  of  the 
alveoli. 

Notwithstanding  these  results,  which  need  further  investiga- 
tion, diffusion  is  usually  regarded  as  the  principal  factor  in  de- 
termining the  gaseous  interchanges  between  the  air  and  the  blood. 

Causes  of  the  Interchange ,  of  O  and  CO2  between 
the  Blood  and  the  Tissues. — This  process  constitutes  in- 
ternal respiration. 

Oxygen  when  it  reaches  the  tissues  by  the  blood  is  immediately 
taken  up  by  them  and  enters  into  chemical  combination,  so  that 
as  oxygen  it  may  be  said  not  to  exist,  except  momentarily.  On 
the  other  hand,  the  tension  of  oxygen  in  arterial  blood  is  rela- 
tively high,  so  that  its  passage  from  the  blood  to  the  tissues  is 
readily  accounted  for.  The  tension  of  CO2  in  the  tissues  is  about 
58  mm.  of  mercury  higher  than  in  the  blood ;  hence  its  passage 
outward  from  the  tissues  to  the  blood. 

Innervation  of  the  Respiratory  Apparatus.— The  nerv- 
ous supply  to  the  respiratory  apparatus  comes  from  the  respiratory 
center,  a  collection  of  nerve-cells  in  the  lower  part  of  the  medulla 
oblongata,  though  its  exact  location  is  not  yet  determined.  Other 
centers,  subsidiary  centers,  have  been  described,  but  their  inde- 
pendence of  the  principal  center  is  questioned. 

The  respiratory  center  is  in  reality  made  up  of  two  centers, 
one  for  each  side,  so  that,  although  anatomically  connected  and 
ordinarily  acting  together,  yet  if  one  center  is  broken  up,  while 
the  respiratory  movements  on  that  side  cease,  those  on  the  other 
side  continue. 

Besides  this  double  character  of  the  center,  each  half  is  made 
up  of  an  inspiratory  and  an  expiratory  center — i.  <?.,  the  nervous 
impulses  which  originate  and  pass  out  from  the  inspiratory  center 
produce  inspiratory  movements,  and  those  from  the  expiratory 
center  bring  about  movements  of  expiration. 

The  respiratory  center  is  both  an  automatic  and  a  reflex  center 
— L  e.j  it  sends  out  spontaneously  impulses  which  result  in  move- 
ments of  the  respiratory  muscles,  constituting  its  automatism  ;  and 
it  may  also  be  excited  reflexly — i.  e.9  by  impulses  reaching  it  from 
without.  Its  reflex  character  is  most  marked,  and  it  is  doubtless 
as  a  reflex  center  that  its  function  is  ordinarily  performed. 

Rhythm  of  the  Respiratory  Movements.— One  of  the 
striking  characteristics  of  the  respiratory  movements  is  their 


CHEMISTRY  OF  RESPIRATION.  387 

rhythmicality — i.  e.,  the  regularity  with  which  expiration  follows 
inspiration,  then  a  pause,  and  again  an  inspiration  followed  by  an 
expiration.  It  is  true  that  this  regularity  is  not  as  marked  in  the 
aged  and  in  phildren  as  in  others,  but  in  a  condition  of  health  it  is 
not  markedly  departed  from.  In  certain  forms  of  disease,  how- 
ever, the  respiratory  movements  are  very  irregular.  One  such  is 
Cheyne-Stokes  respiration  (Fig.  213),  which  may  occur  in  fatty 
degeneration  of  the  heart,  uremia,  some  brain  diseases,  etc.  It  is 


FIG.  213.— Cheyne-Stokes  respiration  (after  Waller). 

characterized  by  a  beginning  shallowness  of  respiration,  the  respi- 
rations gradually  becoming  deeper  and  deeper,  then  a  return  to 
shallowness,  and  finally  a  complete  cessation  of  respiratory  move- 
ments. This  pause  lasts  for  half  a  minute  or  more,  when  the 
shallow  movements  begin  as  before,  followed  by  deeper  and  again 
by  shallower  respirations  and  then  by  a  pause,  etc.  This  grouping 
of  the  respirations  is  shown  in  the  above  curve  of  this  kind  of 
breathing. 

In  all  reflex  acts  not  only  must  there  be  nerve-centers  which 
receive  the  impulses  coming  from  without  and  those  which  gen- 
erate and  emit  impulses,  but  there  must  be  afferent  nerves  to  carry 
the  impulses  to  the  centers  and  efferent  nerves  to  carry  the  outgoing 
impulses.  The  main  afferent  respiratory  nerve  is  the  vagus  or 
pneumogastric,  and  it  has  been  demonstrated  that  this  nerve  con- 
tains two  kinds  of  nerve-fibers — one  which  carries  the  impulses  to 
the  inspiratory  and  the  other  to  the  expiratory  center,  so  that 
division  of  one  nerve  slows  and  deepens  respiration  to  some  degree, 
much  more  when  both  nerves  are  divided.  If  the  end  still  in 
communication  with  the  nerve-centers,  the  central  end,  is  stimu- 
lated powerfully  with  electricity,  the  movements  of  inspiration 
become  greater,  and  the  diaphragm  not  only  contracts — i.  e.,  de- 
scends— but  remains  in  the  position  of  contraction.  If,  on  the 
other  hand,  only  a  weak  stimulus  is  applied,  the  expiratory  move- 
ments are  increased,  and  the  diaphragm  remains  in  the  position  it  is 
in  at  the  end  of  expiration.  It  has  further  been  demonstrated  that 
whenever  air  is  pumped  into  the  lungs  so  as  to  distend  them,  the 
contraction  of  the  diaphragm  diminishes,  and  when  fully  distended 
the  diaphragm  is  in  the  expiratory  position — i.  e.,  as  it  is  at  the 
end  of  an  expiration.  This  distention  of  the  lungs  constitutes 
positive  ventilation.  On  the  other  hand,  if  air  is  pumped  out  of 


388  RESPIRATION. 

the  lungs,  the  alveoli  collapse,  and  the  contractions  of  the 
diaphragm  increase,  and  finally  the  diaphragm  becomes  quiescent 
in  the  inspiratory  position.  Analogous  conditions  occur  in  normal 
breathing.  When  the  lungs  are  distended,  as  in  inspiration,  the 
expiratory  fibers  of  the  vagus  are  stimulated,  and  an  expiratory 
act  follows ;  when  expiration  is  complete  and  the  alveoli  are  in 
the  condition  of  diminished  size,  it  can  hardly  be  called  collapse  ; 
the  inspiratory  fibers  are  stimulated  and  an  act  of  inspiration 
occurs. 

Other  afferent  respiratory  nerves  are  the  superior  laryngeal, 
glossopharyngeal,  trigeminus,  and  sensory  nerves  of  the  skin. 

The  superior  laryngeal  is  the  sensory  nerve  of  the  larynx,  and 
whenever  any  foreign  body  touches  this  sensitive  organ,  or  when 
food  is  inclined  to  go  down  the  "  wrong  way  " — i.  e.,  gets  into  the 
larynx  instead  of  the  esophagus — inspiration  is  at  once  stopped  and 
violent  coughing  ejects  it.  In  this  process  the  afferent  impulses 
are  carried  to  the  respiratory  center,  and  not  only  is  the  inspiratory 
center  restrained  or  inhibited,  but  the  expiratory  center  is  stimu- 
lated, and  a  pronounced  expiratory  effort,  the  cough,  results. 

The  glossopharyngeal  is  also  an  afferent  respiratory  nerve,  and 
carries  to  the  inspiratory  center  inhibitory  impulses  that  cause  all 
inspiratory  movements  to  cease,  as  when  food  is  swallowed.  The 
food  stimulates  the  terminations  of  the  nerve  in  the  mucous  mem- 
brane of  the  pharynx,  and  the  inhibition  results.  Were  this  not 
so,  there  would  be  danger  of  food  entering  the  larynx  at  the  time 
of  inspiration. 

The  trigeminus  sends  fibers  to  the  mucous  membrane  of  the  nose, 
and  when  these  fibers  are  irritated  by  an  irritant  like  ammonia, 
respiration  may  be  arrested. 

The  nerves  of  the  skin  also  act  as  afferent  respiratory  nerves,  as 
is  well  shown  when  cold  water  is  dashed  on  the  body. 

The  efferent  respiratory  nerve's  are  the  phrenics,  which  supply 
the  diaphragm  ;  the  vagi,  which  supply  the  muscles  concerned  in 
producing  the  respiratory  movements  of  the  glottis  (p.  373) ;  and 
the  spinal  nerves,  which  supply  the  respiratory  muscles  of  the 
thorax. 

There  are  certain  terms  used  in  connection  with  respiration 
which  need  to  be  understood. 

Eupnea. — This  term  means  easy  respiration,  and  is  applied  to 
the  normal  act. 

Apnea. — This  term  as  used  by  physiologists,  physiologic 
apnea,  applies  to  a  condition  in  which  the  respiratory  movements 
are  suspended,  as  when  the  lungs  are  distended  with  air  forced  in 
by  a  pair  of  bellows.  It  was  formerly  attributed  to  the  hyper- 
oxygenation  of  the  blood,  but  this  cannot  be  the  only  explanation, 
because  if  hydrogen  is  the  distending  gas,  apnea  results.  Disten- 
tion  with  air  is  practically  what  has  been  described  as  positive 


VOICE  AND  SPEECH.  389 

ventilation.  It  appears,  however,  from  experiments  that  when  the 
lungs  have  been  distended  with  air,  there  is  besides  the  distention 
enough  oxygen  in  the  alveoli  to  aerate  the  blood  for  a  time,  so  that 
it  is  probable  that  physiologic  apnea  is  produced  by  positive 
ventilation,  distention,  and  the  excess  of  oxygen  in  the  alveoli. 
Apnea  is  also  used  as  a  synonym  for  asphyxia ;  in  this  case  the 
qualifying  adjective  "  physiologic J'  is  omitted. 

Dyspnea. — This  is  difficult  or  labored  breathing.  If  caused 
by  a  deficiency  of  oxygen,  it  is  0-dyspnea;  if  by  an  excess  of 
carbon  dioxid,  C02-dyspnea. 

Hyperpnea. — In  this  form  of  breathing  the  rate  is  moderately 
accelerated. 

Asphyxia. — The  term  literally  means  pulselessness,  and  is  espe- 
cially applicable  to  the  last  stage. 

If  by  any  means  the  supply  of  air  to  an  animal  is  cut  off,  or 
so  diminished  in  amount  as  to  be  exhausted,  the  animal  dies  in  a 
short  time  from  asphyxia,  passing  previous  to  the  fatal  termination 
through  the  following  stages  : 

(1)  Hyperpnea. — This  stage  is  characterized  by  an  increased 
frequency  of  the  respiratory  movements,  especially  marked  during 
inspiration,  because  of  the  increased  stimulation  of  the  inspiratory 
center. 

(2)  Dyspnea. — In   this   stage,  the  expiratory  center  is  espe- 
cially stimulated,  and  as  a  result  the  movements  of  expiration 
are   more   pronounced   than  those  of  inspiration,  the  expiratory 
muscles  (p.  371)  being  brought  into  action.     These  two  stages  last 
about  one  minute. 

(3)  Convulsion. — This   stage    is   characterized   by   convulsive 
movements  throughout  the  body. 

(4)  Exhaustion. — The  expiratory  muscles  being  exhausted,  the 
animal  becomes  quiescent,  only  a  few  slight  attempts  at  inspiration 
being  perceptible.     After  a  time  these  become  deeper,  but  only 
occur  at  comparatively  long  intervals. 

(5)  Inspiratory  Spasm. — The  intervals  between  the  inspirations 
have  in  this  stage  greatly  increased,  and  apparently  ceased,  but 
they  recur  occasionally.     The  pupils  are  dilated  and  the  pulse 
becomes  less  and  less  perceptible ;  finally  a  last  inspiration  occurs 
and  the  animal  is  dead. 


VOICE  AND  SPEECH. 

The  voice  is  produced  by  the  vibration  of  the  true  vocal  cords, 
vocal  bands,  or  vocal  ligaments,  by  all  of  which  terms  they  are 
called,  these  being  set  in  vibration  by  the  respired  air  as  it  passes 
out  from  the  lungs,  if  at  the  time  the  bands  are  approximated  and 
tense,  and  if,  also,  the  current  of  air  is  sufficiently  strong.  At  the 
same  time,  the  sounds  produced  by  the  vibrating  bands  are  sup- 


390  VOICE  AND  SPEECH. 

piemen  ted  by  the  cavities  above  and  below  them,  which  act  as 
resonators.  For  the  anatomy  of  the  larynx  the  reader  is  referred 
to  page  354 ;  in  order  to  understand  voice-production  a  knowl- 
edge of  the  anatomy  of  this  organ  is  absolutely  essential.  Especial 
attention  should  be  paid  to  the  muscles  and  their  action. 

I/aryngoSCOpe. — In  order  to  observe  the  changes  which  take 
place  in  the  vocal  bands,  use  is  made  of  the  laryngoscope.  This 
instrument  also  enables  the  physician  to  study  the  other  structures 
of  the  larynx  and  trachea,  and  to  treat  any  diseases  of  these  organs 
which  may  be  present. 

The  laryngoscope  consists  of  a  concave  head-mirror  with  an 
aperture  in  its  center,  and  one  or  more  small  hand-mirrors.  The 


10 


FIG.  214. — The  laryiigoscopic  image  in  easy  breathing :  1,  base  of  the  tongue ;  2, 
median  glosso-epiglottic  ligament ;  3,  vallecula ;  4,  lateral  glosso-epiglottic  ligament ; 
5,  epiglottis  ;  6.  cushion  of  epiglottis ;  7,  cornu  major  of  hyoid  bone ;  8,  ventricular 
band,  or  false  vocal  cord  ;  9,  true  vocal  cord  ;  opening  of  the  ventricle  of  Morgagui 
seen  between  8  and  9 ;  10,  folds  of  mucous  membrane ;  11,  sinus  pyriformis ;  12,  car- 
tilage of  Wrisberg ;  13,  aryteno-epiglottic  fold ;  14,  rima  glottidis ;  15,  arytenoid 
cartilage  ;  16,  cartilage  of  Santorini ;  17,  posterior  wall  of  pharynx  (Stoerk). 

person  whose  larynx  is  to  be  inspected  is  seated  at  the  side  of  a 
lamp,  gas,  or  electric  light,  and  in  front  of  him  is  seated  the 
observer,  with  the  head-mirror  so  attached  that  he  can  look 
through  the  aperture  in  its  center.  The  observed  now  opens 
his  mouth,  the  head  being  thrown  back,  and  with  a  napkin  the 
tongue  is  drawn  out  and  its  tip  is  held  against  the  lower  teeth,  by 
which  act  the  epiglottis  is  drawn  forward.  One  of  the  hand- 
mirrors  is  then  slightly  heated  and  passed  into  the  mouth,  its  back 
elevating  the  uvula ;  the  head-mirror  is  then  so  directed  as  to  re- 
flect the  light  on  the  hand-mirror  and  illuminate  the  image  formed 
by  it  of  the  larynx  and  trachea.  If  the  hand-mirror  is  not  heated, 
the  vapor  of  the  expired  air  will  be  condensed  upon  it,  obscuring 
the  reflected  image.  To  avoid  overheating  it  and  burning  the 


RESONANCE. 


391 


parts  of  the  throat  with  which  it  comes  in  contact,  the  observer 
touches  it  to  the  back  of  his  hand  before  introducing  it. 

The  image  which  is  seen  (Fig.  214)  is  reversed — i.  e.9  the 
epiglottis  appears  in  the  upper  portion  of  the  image,  and  the  left 
side  of  the  larynx  is  at  the  right,  as  seen  by  the  observer. 

Laryngoscopic  Image  during  Respiration. — If  the  glottis  is  ex- 
amined in  the  cadaver,  the  separation  of  the  bands  is  but  about 
1  or  2  mm.,  while  during  life,  when  ordinary  or  quiet  breathing  is 
taking  place,  the  separation  amounts  to  3  to  4  mm.  Nor  is  there, 
in  most  individuals,  much  difference  between  ordinary  inspiration 
and  expiration  as  to  the  width  of  the  opening,  although  in  some 
the  bands  do  separate  a  little  during  inspiration  and  again 
approach  during  expiration.  During  deep  inspiration  the  width 
of  the  rima  glottidis  may  be  1.3  cm. 

Laryngoscopic  Image  during  Voice-production  or  Phonation. — 
When  a  tone  is  produced  the  vocal  bands  approach  each  other  and 
are  rendered  more  tense ;  and  the  greater  the  tension  the  higher 
is  the  note.  Although  in  the  production  of  a  high  note  the  cords 
are  correspondingly  approximated,  still  this  does  not  seem  to  be 
essential,  while  increased  tension  of  the  cords  is  absolutely  neces- 
sary to  the  production  of  a  more  elevated  tone.  It  is  claimed 
that  the  depression  of  the  epiglottis  and  its  consequent  partial 
covering  of  the  glottis  render  the  tones 
produced  by  the  vibrating  bands  lower 
in  pitch,  and  that  the  epiglottis  also  acts 
as  a  sounding-board  by  reinforcing  the 
vibrations  of  the  air-column  which  im- 
pinges against  it. 

Resonance. — This  is  defined  as 
"  A  prolongation  or  reinforcement  of 
sound  by  means  of  sympathetic  vibra- 
tion, or  the  capability  of  producing  such 
a  continued  sound"  (Standard  Diction- 
ary) :  or  u  The  property  of  a  sonorous 
body  that  enables  it  to  absorb  the  vibra- 
tions of  another  sonorous  body  and  vi- 
brate in  unison  with  it7'  (Wentworth 
and  Hill). 

Bodies  which  possess  this  property 
are  resonators,  and  good  examples  are 
resonant  boxes,  such  as  the  body  of  a 
violin,  which  contain  masses  of  air. 
The  action  of  a  resonator  is  illustrated 

and  explained  as  follows  (Fig.  215) :  If  a  vibrating  tuning-fork  is 
held  over  the  mouth  of  a  cylindrical  jar,  of  about  2  inches  diam- 
eter and  12  inches  deep,  and  water  is  poured  in  slowly,  it  will  be 
noticed  that  as  the  air-column  grows  shorter,  the  sound  grows 


FIG.  215. — Tuning-fork  and 
cylindrical  jar,  to  illustrate  reso- 
nance (Carhart  and  Chute). 


. 


.-  -  : 


: 


3t 


-  -  :-—-•- 


:  -  —  —     - 

•EBTC 


- 


_ 


:- 


- 
- 
• 


of 

FiiLwhh  44 
mmg.  to  far  as  is 

toons  per  second.     This  note  was  m 
delia.~ 

Qmllalj       n  Inil    In  .iefine-  the 
pet  •tin  in  which 
that  of  a  flute,  or 

all 

r    The  m 
fundamental  and 
thane  of  the  cavities  of  the 


(2)  "  a  ek*  or 
to  a  parcicolaf 


the  chest  wffl  be  tit  to 


*y 

noticed 

quality  of  the 

from  on 

rvpufer.  and 

if  one  places  one's  hand  upon  h.  and  the 

.-  above  this  is  the  • 
all  is  the  feocf 


to 

emitted,  and  said  to  be  doe  to 

the  cords  only.     The  iaketto  nav  be 

ister.     FV>f.  tbc^  R.  Freneh  is  if  the 

voices  with  exceptional  QUIT-  there  are  loor 
cient  evidence  has  not  yet  been  obtained  10 
•table.'9 

Speech. — Phooatk«u  or  vi«^-|Nr^h>rrii(«.  is  a 
to  all  animals  havinr  vocal  bands,  while  the  farahv  of 


to  an  anuuais  navmg  vocai  oanosw  wn 
peculiar  to  man.  Channin^  says :  -  A 
up  his  mind  in  itsehu  but  to  give  it  w 


_^^  _-    __^_J,=.        ^> m.    •      _^ 

oiner  nnnns*    cipeecn  E  one  en 

brute.""     It  is  possible  that  this  attnbiHe  of  man  maty  not  be 


394  VOICE  AND  SPEECH. 

made  which  would  lead  to  the  conclusion  that  they  can  communi- 
cate to  a  certain  extent  with  their  fellows. 

Vowels. — These  are  sounds  produced  by  vibrations  of  the 
vocal  bands,  but  modified  by  the  resonating  cavities,  to  which 
modification  the  difference  in  their  quality  is  due  :  and  if  the 
variations  in  the  cavity  of  the  mouth  together  with  those  of  the 
tongue  and  soft  palate  are  observed  while  different  vowels  are 
sounded,  this  fact  will  be  readily  understood  (Fig.  216). 

Consonants. — These  are  not  produced  by  the  vocal  bands  as 
are  the  vowels,  but  by  obstructions  placed  in  the  way  of  an  out- 
going blast  of  air;  and  places  where  these  obstructions  are  placed 
are  positions  of  articulation.  "  The  consonants  are  classified  ac- 
cording to  (1)  their  places  of  closure ;  (2)  the  completeness  of  the 
closure ;  (3)  their  utterance  with  breath  or  voice.  The  first  dis- 
tributes them  into  (a)  labials,  or  lip-consonants — p,  f,  b,  v,  m,  w ; 
(6)  dentals,  or  tooth-consonants — t,  d,  th,  dh  ;  (c)  palatab,  or  palate- 


\  \ 

FIG.  216.— Section  of  the  parts  concerned  in  phonation,  and  the  changes  in'their 
relations  m  sounding  the  vowels  A  («»),  /(«),  U  (<") ;  T,  tongue  -,  p,  soft  palate  ;  e, 
epiglottis;  g,  glottis;  *,  hyoid  bone ;  1,  thyroid ;  2,  3,  cricoid;  4,  arytenoid  cartilage 
(after  Landois  and  Stirling). 

consonants,  including  sibilants— s,  z,  sh,  zh,  and  liquids,  1,  v,  n,  y  ; 
(d)  gutturals,  or  throat-consonants— c-k,  ch  (Scottish  lock),  g,  gh, 
(Irish  lough),  h,  ng. 

"  The  second  division  gives  mutes,  having  tight  closure— p,  b, 
t,  d,  c-k,  g ;  the  other  consonants  are  continuous. 

"The  third  division  gives  :  (1)  Surds— p,  t,  ch,  c  (k),  f,  th  (as  in 
thin)  s  sh,  h.  (2)  Sonants--*,  d,  j,  g,  v,  dh,  z,  zh,  w,  1,  r,  y,  m, 
n,  ng  (Standard  Dictionary). 

Photography  of  the  Xarynx.— Prof.  Thomas  R.  French, 
of  the  Long  Island  College  Hospital,  has  brought  larvngeal  pho- 
tography to  a  high  state  of  perfection,  and  has  demonstrated  most 
thoroughly  the  changes  which  take  place  in  the  vocal  bands  during 
the  act  of  singing.  The  results  of  his  observations  are  recorded 
m  the  New  York  Medical  Journal.  To  him  we  are  indebted  for 
our  present  knowledge  of  this  important  subject,  and  from  his 
articles  m  this  publication  we  quote  freely ;  the  illustrations  are 
also  taken  from  the  same  source. 


PHOTOGRAPHY  OF  THE  LARYNX. 


395 


In  photographing  the  larynx,  Prof.  French  uses  the  electric  arc 
light.  The  apparatus  is  shown  in  Fig.  217.  It  consists  of  an 
automatic  2000-candle-power  lamp  partly  inclosed  in  a  metal  box. 
The  front  face  of  the  box  carries  a  condensing  lens  which,  when 
placed  9  inches  from  the  arc,  gives  a  focal  distance  of  20  inches. 
This  relation  of  light  and  lens  is  found  to  give  the  most  satisfac- 
tory illumination.  The  lamp  and  accessories  are  fitted  to  a  narrow 
board  which  is  placed  upon  a  table  of  sufficient  height.  The  light 
can  be  raised  or  lowered  by  means  of  a  device  designed  for  that 
purpose.  The  rheostat  is  placed  upon  a  shelf  beneath  the  table 
top.  The  whole  light  outfit  is  but  a  modification  of  the  electric 
stereopticon.  This  one  is  so  arranged  that  by  adding  a  second 


FIG.  217. — Showing  the  manner  in  which  photographs  of  the  larynx  and  posterior 
uares  are  secured  with  the  aid  of  the  arc  light. 

condensing  lens  and  an  objective  lens  to  the  end  of  the  cone- 
shaped  tube  in  front  it  can  be  used  as  a  projecting  lantern. 

In  speaking  of  the  action  of  the  glottis,  Prof.  French  says  that 
with  all  his  experience  he  has  not  yet  permitted  himself  to  formu- 
late a  theory  of  the  action  of  the  glottis  in  singing,  for  even  now, 
after  a  large  number  of  studies  have  been  made,  the  camera  is  con- 
stantly revealing  new  surprises  in  the  action  of  the  vocal  bands 
in  every  part  of  the  scale.  The  movements  of  the  larynx  in  a 
much  larger  number  of  subjects  must  be  revealed,  grouped,  and 
recorded  before  definite  conclusions  can  be  drawn. 

Most  of  our  past  knowledge  on  the  subject  of  the  changes  in 
the  larynx  during  singing  has  been  obtained  from  inspection  of 
this  organ  through  the  laryngoscope.  As  these  changes  follow 
each  other  too  rapidly  to  be  appreciated  by  the  eye,  much  of  this 
knowledge  has  been  found  to  be  erroneous.  The  photographic 


396 


VOICE  AND  SPEECH. 


plate,  however,  is  so  sensitive  that  every  detail  can  be  recorded, 
and  as  a  result  of  its  application  to  the  physiology  of  the  larynx, 
ranch  that  was  regarded  as  established  has  been  demonstrated  to 
be  false :  just  as  the  older  ideas  of  the  form  of  a  lightning-flash 
have  been  entirely  changed  by  instantaneous  photography. 

The  difficulties  to  be  overcome  in  photographing  the  larynx  so 
as  to  show  the  changes  during  voice-production  are  many,  among 


FIG.  218.— Apparatus  used  in  photographing  the  larynx. 

them  being  the  fact  that  it  is  only  in  certain  individuals  that  the 
vocal  bands  can  be  seen  throughout  their  whole  length.  This  is 
very  well  shown  in  Fig.  220.  In  No.  1  the  insertions  of  the 
vocal  bands  into  the  thyroid  cartilage  are  so  exposed  as  to  be  sus- 
ceptible of  being  photographed ;  in  No.  2  these  are  covered  by 
the  anterior  wall  of  the  larynx,  and  it  would  therefore  be  impos- 
sible to  determine  in  such  a  larynx  whether  the  vocal  bands  were 
lengthened  or  shortened  in  passing  from  one  register  to  another, 


PHOTOGRAPHY  OF  THE  LARYNX 


397 


or  during  a  change  in  the  pitch  of  the  voice.  In  some  individuals 
the  bands  will  be  exposed  throughout  their  length  while  some 
notes  are  being  sung,  while  during  the  singing  of  others  they  will 
be  covered.  Fig.  221  shows  this ;  while  singing  F  sharp  and  D, 
the  bands  are  exposed,  but  covered  when  E  is  being  sung.  The 
number  of  persons  whose  larynges  are  so  constructed  as  to  permit 
photographing  to  determine  the  changes  taking  place  in  the  glottis 


FIG.  219. — Photograph  taken  by  Prof.  French  of  a  normal  larynx  in  quiet  respiration. 

throughout  all  the  registers  is,  it  will  be  seen,  limited,  and  who 
they  are  can  only  be  ascertained  by  careful  inspection.  Nor  are 
the  changes  which  take  place  the  same  in  all  individuals. 

The  following  photographs  show  these  changes  in  the  larynx 
of  a  well-known  professional  contralto  singer,  and  their  explana- 
tion will  be  given  in  Prof.  French's  words : 


No.l. 


No.  2. 


FIG.  220.— PAIR  1. 


"  The  voice  in  this  singer  is  of  excellent  quality.  The  first 
of  the  pair  (Fig.  222,  No.  1)  was  taken  while  F  sharp,  treble  clef, 
third  line  below  staff,  was  being  sung,  and  the  second  (No.  2)  while 
she  was  singing  E  above.  All  notes  in  this  and  the  following  series 
were  sung  in  the  key  of  A.  These  are  one  of  the  lowest  and  the 
highest  notes  of  her  lower  register.  In  the  photograph  represent- 
ing the  lowest  note  it  can  be  seen  that  the  vocal  bands  are  quite 


398 


VOICE  AND  SPEECH. 


short  and  wide,  and  that,  with  the  exception  of  the  anterior  fourth, 
the  ligaraentous  and  a  part  of  the  cartilaginous  glottis  is  open  and 
the  slit  between  the  vocal  bands  is  linear  in  shape.  As  the  voice 
ascends  the  scale  the  vocal  bands  increase  in  length  and  decrease  in 
width,  until  at  the  highest  note  of  the  register  they  can  be  seen  to 
have  become  considerably  longer.  It  can  also  be  observed  that  the 
ligamentous  portion  of  the  glottis  is  still  open  to  the  same  relative 
extent,  and  that  the  cartilaginous  portion  has  opened  to  its  full  ex- 
tent. In  the  photograph  representing  the  lower  note  the  anterior 
faces  of  the  arytenoid  cartilages  can  be  seen.  As  the  voice  ascended, 
the  capitula  Santorini  were  tilted  forward.  This  seems  to  be  proved 


E 


FIG.  221. 


by  the  change  in  the  position  of  these  structures  as  seen  in  the 
photograph  representing  the  upper  note,  as  well  as  a  similar  change 
to  be  seen  in  nearly  all  the  series  showing  the  registers  which  I 
have  taken.  The  epiglottis,  though  not  well  illuminated,  seems 
to  have  risen  as  the  voice  ascended"  the  scale.  The  light  upon  the 
epiglottis  is  so  weak  that  the  structure  does  not  appear  at  all  in 
the  photo-engraving.  The  vocal  bands  have  increased  in  length 
at  least  £  inch  in  7  notes.  The  compass  of  the  voice  of  this  sub- 


PHOTOGRAPHY  OF  THE  LARYNX. 


399 


ject  is  about  2-J  octaves.  Therefore,  at  that  rate  of  lengthening, 
the  vocal  bauds  would  increase  nearly  ^  inch  if  their  length  was 
progressively  increased  while  singing  up  the  scale  from  the  lowest 
to  the  highest  note.  This  progressive  increase  in  length  does  not, 


No.  1. 


FIG.  222.— PAIR  2. 


No.  2. 


however,  occur,  and  the  reason  is  apparent  in  Fig.  223,  which 
shows  the  changes  which  took  place  in  the  larynx  at  the  lower 
break  in  the  voice,  which,  in  this  subject,  occurs  at  F  sharp,  treble 
clef,  first  space. 


No.  1. 


FIG.  223.— PAIR  3. 


No.  2. 


"  The  changes  which  occur  at  this  point  are  extremely  inter- 
esting and  instructive.  In  the  transition  from  the  lower  to  the 
middle  register,  from  E  to  F  sharp,  in  the  voice  of  this  subject, 
the  vibratory  portions  of  the  vocal  bands  are  shortened  about  ^ 


400  VOICE  AND  SPEECH. 

inch.  The  anterior  insertions  of  the  vocal  bands  can  be  seen  in 
both  photographs ;  therefore  the  actual  difference  in  the  length  of 
the  bands  can  be  appreciated.  The  vocal  bands  have  not  only 
become  shorter,  but  they  appear  to  be  subjected  to  a  much  higher 
degree  of  tension.  The  cartilaginous  glottis  is  closed  and  the 
aperture  in  the  ligamentous  portion  has  been  much  reduced  in 
size.  The  laws  which  govern  the  pitch  in  both  string  and  reed 
instruments  will  aid  us  in  explaining  these  changes.  Though  the 
tone  is  higher  and  the  degree  of  stretching  less  than  in  the  note 
below,  the  tension  is  increased,  and  the  aperture  through  which 
the  air  passes  is  much  narrower.  It  seems  to  me  that  this  clearly 
defined  change  in  the  mechanism  of  the  vocal  bands — which,  so 
far  as  my  investigations  permit  me  to  judge,  are  at  this  point  in 
the  scale  the  rule— will  assist  us  to  a  clear  understanding  of  the 
action  of  the  laryngeal  muscles  in  singing  when  we  reach  that 
part  of  the  study. 

"  In  the  first  photograph,  which  was  taken  while  the  subject 
was  singing  the  note  immediately  preceding  that  on  which  the 
break  occurred,  the  vocal  bands  can  be  seen  to  be  long  and  wide 
and  the  posterior  three-fourths  of  the  chink  of  the  glottis  is  open. 
By  open,  I  mean  that  the  edges  of  the  vocal  bands  are  not  in 
actual  contact.  The  anterior  fourth  or  fifth  of  the  ligamentous 
portion  of  the  glottis  is  closed.  The  space  between  the  vocal 
bands  is  widest  in  the  cartilaginous  portion  of  the  glottis.  In 
the  production  of  the  next  note  higher,  F  sharp,  the  second  of  the 
pair,  a  marked  change  in  the  size  of  the  larynx  and  in  the  length 
of  the  vocal  bands  is  seen  to  have  occurred.  The  cavity  of  the 
larynx  has  been  suddenly  reduced  in  size  and  the  vocal  bands 
have  been  shortened.  The  cartilaginous  portion  of  the  glottis  is 
closed  and  the  ligamentous  portion  is  open  in  a  linear  slit  from 
the  posterior  vocal  process  to  within  a  short  distance  of  the  an- 
terior insertions  of  the  vocal  bands.  The  decrease  in  the  length 
of  the  vibratory  portions  of  the  vocal  bands  is  due  to  the  closure 
of  the  cartilaginous  glottis,  for  the  ligamentous  glottis  remains 
about  the  same  as  in  the  note  before  the  break.  The  arytenoid 
cartilages  have  been  brought  much  closer  together  and  occupy  a 
more  posterior  position.  These  pictures  were  taken  one  after  the 
other  in  quick  succession,  the  conditions  in  every  respect,  except 
the  note  sung,  being  the  same.  The  anteroposterior  and  lateral 
dimensions  of  the  cavity  of  the  larynx  are  shown  to  have  been 
considerably  decreased  when  the  voice  broke  into  the  register 
above.  When  the  mechanism  of  the  larynx  was  changed  the 
voice  acquired  a  very  different  quality,  which  continued,  in  grad- 
ual elevation  of  pitch,  throughout  the  register.  As  marked  a 
change  as  this  in  the  mechanism  of  the  vocal  bands  in  females  is, 
I  believe,  found  only  in  the  larynges  of  contralto  singers. 

"  It  is  believed  by  many  writers  on  the  voice  that  with  the 


PHOTOGRAPHY  OF  THE  LARYNX.         401 

change  in  the  mechanism  of  the  vocal  bands  the  epiglottis  is 
raised  higher  than  in  the  register  below.  I  am  of  the  opinion 
that  it  is  usually  depressed.  The  reason  for  this  belief  is  that, 
with  very  few  exceptions,  I  have  found  it  lower  in  the  photo- 
graphs showing  the  change  than  in  those  representing  the  note 
preceding  it.  When  the  voice  of  this  subject  broke  into  the 
middle  register  it  was  with  difficulty  that  T  could  get  the  epiglottis 
to  rise  as  high  as  it  is  shown  here,  which,  though  high  enough  to 
show  the  anterior  insertions,  is  not  so  high  as  it  was  before  the 
break.  There  does  not  seem  to  be  any  difference  in  the  width  of 
the  vocal  bands,  but  in  this  particular  the  appearances  vary,  the 
variation  being  due  to  the  position  of  the  ventricular  bands.  The 
entire  upper  surfaces  of  the  vocal  bands  are  rarely  exposed  to 
view  during  the  production  of  the  middle  and  upper  notes. 


No.  1.  No.  2. 

FIG.  224.— PAIR  4. 

"  As  this  singer  ascends  the  scale  above  the  break  at  F  sharp, 
the  vocal  bands  are  increased  in  length  and  the  chink  gradually 
enlarges,  as  shown  in  Fig.  224.  The  first  photograph  is  of  the 
larynx  while  singing  F  sharp,  treble  clef,  first  space,  the  note  on 
which  the  lower  break  occurred,  and  the  second  while  singing  D, 
treble  clef,  fourth  line,  which  is  the  highest  note  in  the  middle 
register  of  the  voice  of  this  singer.  The  difference  in  the  length 
of  the  vocal  bands  and  width  of  the  chink  of  the  glottis,  as  the 
voice  mounts  from  the  lowest  to  the  highest  note  of  the  middle 
register,  is  clearly  shown.  Not  only  is  it  shown  that  the  vocal 
bands  increase  in  length  as  the  voice  ascends  the  scale,  but  the 
cartilaginous  portion  of  the  glottis — which,  while  producing  the 
lowest  note  of  this  register,  is  seen  to  be  tightly  closed— has 
begun  to  open  again,  as  shown  by  the  small  triangular  opening 
which  has  appeared  between  the  arytenoids  in  the  second  of  this 

26 


402  VOICE  AND  SPEECH. 

pair.  Again,  as  the  vocal  bands  increase  in  length  in  this  register 
their  tension  is  apparently  decreased.  The  capitula  Santorini, 
which  in  the  photograph  representing  the  lowest  note  in  the 
middle  register  are  seen  to  be  close  together  and  occupy  a  position 
well  backward  in  the  laryngeal  image,  become  more  and  more 
separated  and  are  tilted  more  and  more  forward  in  the  ascent  of 
the  scale. 

"  Now  the  voice  mounts  one  note  higher — that  is,  to  E,  treble 
clef,  fourth  space — and  as  it  does  so  a  distinct  change  in  the  qual- 
ity of  the  voice  is  heard,  and  the  second  change  in  the  mechan- 
ism of  the  vocal  bands  occurs.  The  changes  which  take  place  in 
the  larynx  at  the  upper  break  in  the  voice  of  this  singer  are  shown 
in  Fig.  225.  The  first  of  the  pair  represents  the  larynx  while  sing- 
ing D,  treble  clef,  fourth  line,  the  note  immediately  preceding  the 


No.  1.  No.  2. 

FIG.  225.— PAIR  5. 

break,  and  the  second  shows  the  change  which  occurred  while 
singing  E,  the  next  note  above.  A  very  decided  change  in  the 
mechanism  of  the  vocal  bands  is  apparent.  These  ligaments  have 
grown  shorter  and  narrower,  and  the  chink,  which  in  the  note 
before  the  break  can  be  seen  to  be  linear  in  shape  and  quite  wide, 
after  the  break  becomes  considerably  reduced  in  both  length  and 
width.  Not  only  is  the  cartilaginous  portion  of  the  glottis  closed 
in  the  note  after  the  break,  but  also  a  small  portion  of  the  liga- 
mentous  glottis  adjoining  it.  The  chink  appears  to  be  closed 
to  the  same  extent  in  front  as  it  was  while  producing  the  note 
immediately  preceding.  There  is,  therefore,  stop-closure  in  front 
and  behind,  which  leaves  a  slit  in  the  middle  of  the  glottis 
measuring  a  little  more  than  half  the  length  of  the  vocal  bands. 
In  addition  to  these  changes  it  may  be  observed  that  the  epiglottis 
is  depressed  and  the  arytenoid  cartilages  have  again  receded.  As 


PHOTOGRAPHY  OF  THE  LARYNX.  403 

this  is  the  highest  note  which  this  subject  is  capable  of  singing 
with  ease,  we  cannot  study  the  action  of  the  vocal  bands  in  the 
production  of  tones  in  the  upper  register. 

"  It  may  be  remembered  that  in  this  larynx  the  vocal  bands 
increased  in  length  from  the  low  F  sharp  to  the  E  above.  At 
the  next  note  above  they  were  suddenly  shortened.  At  the  next 
note  higher  they  began  to  increase  in  length  again,  until  D,  above, 
was  reached,  and  at  E,  the  note  next  above,  they  were  again  sud- 
denly shortened.  It  will  be  instructive  to  determine  the  degree 
to  which  the  vocal  bands  were  lengthened  and  at  what  point  in 
the  scale  they  were  longest.  We  saw  that  in  the  lower  register 
the  vocal  bands  were  longest  in  the  production  of  the  highest 
note,  and  in  the  middle  register  they  were  also  longest  while  the 
highest  note  was  being  sung.  By  comparing  the  photographs 
representing  these  notes  (Fig.  226)  it  can  be  seen  that  the  vocal 
bands  were  as  long,  if  not  the  longest,  while  the  highest  note  of 
the  lower  register  was  being  sung.  In  this  subject  the  vocal 
bands  increase  in  length  in  each  register,  but  they  attain  as  great 
a  length  in  the  lower  as  in  either  of  the  registers  above,  if  not 
greater.  It  is  generally  thought  that  the  pitch  is  raised  by  the 
vocal  bands  increasing  progressively  in  tension  and  length.  In 
regard  to  length  this  is  true  in  some  cases,  while  in  others  it  is 
only  true  as  applied  to  a  register,  not  to  the  whole  of  the  voice. 

"  The  next  series  of  photographs  (not  here  reproduced)  are  of  a 
professional  singer  who  possesses  a  rich  contralto  voice  of  large 
range  and  good  volume.  The  photographs  of  the  larynx  of  this 
subject  are  strong  enough  for  satisfactory  exhibition  upon  the 
screen,  but  too  weak  for  reproduction  by  the  photo-engraving 
process.  Though  this  singer  has  as  large  a  range  as  she  whose 
larynx  we  have  just  investigated,  the  pitch  of  her  speaking 
voice  is  several  tones  higher.  Here  we  shall  find  that  the  larynx 
acts  in  a  very  different  way  from  that  just  examined.  The 
first  photograph  of  this  pair  was  taken  while  F  sharp,  treble  clef, 
third  line  below  staff,  was  being  sung ;  the  second,  while  she  was 
singing  D,  treble  clef,  first  space  below  staff.  The  right  aryten- 
oid  cartilage  overlaps  its  fellow.  In  the  production  of  the  low 
note  the  anterior  insertions  are  covered,  and  we  cannot,  therefore, 
see  how  long  the  vocal  bands  really  are.  The  ligamentous  portion 
of  the  glottis  is  well  open,  the  chink  being  much  wider  behind 
than  in  front.  The  cartilaginous  glottis  appears  to  be  closed,  but 
I  do  not  think  that  it  really  is,  but,  because  of  the  somewhat 
unusual  setting  of  the  arytenoid  cartilages,  the  cleft  between  them 
cannot  be  seen.  As  the  voice  ascends  the  scale  the  epiglottis  is 
raised,  the  vocal  bands  increase  in  length,  and  the  chink  of  the 
glottis  gradually  narrowed  until  at  D,  the  highest  note  of  the 
lower  register,  we  find  that  the  vocal  bands  appear  to  be  consid- 
erably elongated,  the  chink  considerably  reduced  in  width,  and  the 


404  VOICE  AND  SPEECH. 

epiglottis  raised  considerably  higher.  The  cartilaginous  portion 
of  the  glottis  still  appears  to  be  closed,  and  there  is  no  evidence 
of  a  forward  movement  of  the  capitula  Santorini.  When  the  next 
note  higher  was  sung,  a  very  noticeable  change  in  the  quality  of 
the  voice  was  heard,  and,  by  examining  the  photographs  taken 
while  that  note  was  being  sung  with  that  representing  the  note 
below  it,  it  can  be  seen  that  a  slight  change  in  the  mechanism 
occurred.  The  epiglottis  is  depressed.  The  vocal  bands  are 
longer  and  narrower,  their  edges  are  straighter,  and  the  chink  of 
the  glottis,  which  in  the  note  before  the  break  was  closed  in  front, 
has  opened  from  the  anterior  to  the  posterior  commissure,  and  is 
considerably  increased  in  size.  The  cartilaginous  glottis  still 
appears  to  be  closed.  The  arytenoid  cartilage  on  the  right  side 


D 


No.  1.  No.  2. 

FIG.  226.— PAIR  6. 

occupies  the  same  position  as  before  the  break,  but  the  left  has 
moved  a  little  backward. 

"  The  voice  now  ascends  the  scale  until  D,  treble  clef,  fourth 
line,  is  reached,  when  it  can  be  seen  that  the  epiglottis  is  slightly 
raised,  the  vocal  bands  appear  to  be  increased  in  length  and  de- 
creased in  width,  and  the  arytenoid  cartilages  are  turned  further 
forward  and  brought  closer  together.  The  chink  of*  the  glottis  is 
still  open  from  front  to  back,  and  is  altogether  larger  than  in  the 
lower  note  of  this  register.  The  apparent  increase  in  the  length 
of  the  vocal  bands  is  partly  due  to  the  fact  that  the  cartilaginous 
portion  of  the  glottis  is  now  beginning  to  open.  This  note  is  as 
high  as  this  subject  can  sing  with  ease. 

"  In  many  particulars  the  action  of  this  larynx  is  the  reverse 
of  that  just  examined.  In  this  the  cartilaginous  glottis  does  not 
appear  to  begin  to  open  until  the  highest  notes  are  reached.  In 
the  lower  register  the  chink  of  the  glottis  decreases  instead  of  in- 
creases in  size  as  the  voice  ascends.  At  the  lower  break  the  vocal 


PHOTOGRAPHY  OF  THE  LARYNX. 


405 


bands  are  increased  instead  of  decreased  in  length,  and  the  chink 
of  the  glottis  is  increased  instead  of  decreased  in  size.  In  the 
larynx  before  examined  the  chink  of  the  glottis  increased  in  size 
and  the  vocal  bands  increased  in  length  as  the  voice  ascended  in 
each  register,  attaining  their  greatest  length  at  the  highest  note  of 
the  middle  register ;  but  in  this  the  vocal  bands  attained  their 
greatest  length  at  the  highest  note  in  the  voice  of  this  subject, 
which  corresponds  to  about  the  highest  note  of  the  middle  regis- 
ter." 

Figs.  227  and  228  are  from  photographs  of  the  larynx  of  the 
contralto  singer  referred  to  on  page  397,  showing  the  same 
mechanism  of  the  vocal  bands  in  passing  from  the  lower  to  the 
middle  register,  from  E  to  F  sharp,  as  is  shown  in  Fig.  223,  but 
on  a  different  occasion. 


FIG.  227. 


FIG.  228. 


In  concluding  his  Berlin  address,  Prof.  French  says  : 

"  Though  the  number  of  series  of  photographs  which  have  been 
taken  of  the  larynx  in  singing  is  quite  large,  I  do  not  yet  feel 
justified  in  drawing  definite  conclusions  from  them  regarding 
many  of  the  movements  of  the  glottis  at  different  points  in  the 
scale,  but  from  the  study  made  thus  far  the  following  conclusions 
regarding  the  glottis  of  the  female  may,  I  think,  be  safely  drawn : 

"  1.  The  larynx  may  act  in  a  variety  of  ways  in  the  production 
of  the  same  tones  or  registers  in  different  individuals. 

"  2.  The  rule — which,  however,  has  many  exceptions — is  that 
the  vocal  bands  are  short  and  wide  and  the  ligamentous  and  car- 
tilaginous portions  of  the  glottis  are  open  in  the  production  of  the 
lower  tones;  that,  as  the  voice  ascends  the  scale,  the  vocal  bands 
increase  in  length  and  decrease  in  width,  the  aperture  between  the 


406  VITAL  HEAT. 

posterior  portions  of  the  vocal  bands  increases  in  size,  the  capitula 
Santorini  are  tilted  more  and  more  forward,  and  the  epiglottis  rises 
until  a  note  in  the  neighborhood  of  E,  treble  clef,  first  line,  is 
reached.  The  cartilaginous  glottis  is  then  closed.  The  glottic 
chink  becomes  much  narrower  and  linear  in  shape,  the  capitula 
Santorini  are  tilted  backward,  and  the  epiglottis  is  depressed. 

"  When  the  vocal  bands  are  shortened  in  the  change  at  the 
lower  break  in  the  voice,  it  is  mainly  due  to  closure  of  the  carti- 
laginous portion  of  the  glottis,  the  ligamentous  portion  not  usually 
being  affected.  If,  therefore,  the  cartilaginous  glottis  is  not  closed, 
there  is  usually  no  material  change  in  the  length  of  the  vocal 
bands. 

"  As  the  voice  ascends  from  the  lower  break,  the  vocal  bands 
increase  in  length  and  diminish  in  width,  the  posterior  portion  of 
the  glottic  chink  opens  more  and  more,  the  capitula  Santorini  are 
tilted  forward,  and  the  epiglottis  rises  until,  in  the  neighborhood 
of  E,  treble  clef,  fourth  space,  another  change  occurs. 

"  The  glottic  chink  is  then  reduced  to  a  very  narrow  slit,  in 
some  subjects  extending  the  whole  length  of  the  glottis.  In  others, 
closing  in  front,  or  behind,  or  both.  Not  only  is  the  cartilaginous 
glottis  always  closed,  but  the  ligamentous  glottis  is,  I  believe, 
invariably  shortened.  The  arytenoid  cartilages  are  tilted  back- 
ward and  the  epiglottis  is  depressed.  As  the  voice  ascends  in  the 
head  register  the  cavity  of  the  larynx  is  reduced  in  size,  the  aryte- 
noid cartilages  are  tilted  forward  and  brought  closer  together,  the 
epiglottis  is  depressed,  and  the  vocal  bands  decrease  in  length  and 
breadth.  If  the  posterior  part  of  the  ligamentous  portion  of  the 
glottis  is  not  closed  in  the  lower,  it  is  likely  to  be  in  the  upper 
notes  of  the  head  register." 

VITAL  HEAT. 

The  temperature  of  a  lifeless  object  is  approximately  that  of 
the  air  which  surrounds  it ;  the  temperature  of  a  living  object  is 
independent  of  the  temperature  of  the  air,  although  it  may  be 
modified  by  it.  This  difference  is  due  to  the  fact  that  living  things 
produce  heat  within  themselves  ;  this  is  called  "  vital  heat."  Many, 
perhaps  most,  authorities  speak  of  it  as  "  animal  heat,"  but,  though 
it  is  most  striking  in  members  of  the  animal  kingdom,  yet  inas- 
much as  its  production  is  not  confined  to  animals,  but  also  occurs 
in  plants,  the  writer  prefers  the  term  vital  heat  as  indicating  that 
the  phenomenon  is  peculiar  to  the  living  condition,  irrespective  of 
the  question  whether  it  occurs  in  an  animal  or  in  a  vegetable. 

Warm-blooded  Animals. — The  term  warm-blooded  was  ap- 
plied to  certain  animals  because  their  temperature  was  so  high  as 
to  make  them  warm  to  the  touch,  while  others  were  spoken  of  as 
cold-blooded  because  they  were  cold  to  the  touch.  Thus,  man,  with 


TEMPERATURE  OF  DIFFERENT  PARTS  OF  THE  BODY.   407 


a  temperature  of  37°  C.,  the  dog,  39°,  the  cat,  39°,  the  swallow, 
44°  or 'even  higher,  are  among  the  warm-blooded,  while  reptiles 
and  fishes,  whose  temperature  is  from  1.7  degrees  to  4.5  degrees 
C.  above  that  of  the  medium  in  which  they  exist,  are  cold-blooded. 
The  terms  warm-blooded  and  cold-blooded  are,  however,  now  not 
so  frequently  used  as  formerly,  but  in  their  stead  are  used  the  terms 
homoiothermal  and  poikilothermal. 

Homoiothermal  animals  are  animals  of  uniform  heat  or 
those  whose  temperature  is  unvarying.  The  thermometer  if  in- 
troduced into  the  rectum  of  a  man,  whether  he  is  in  the  tropics  or 
in  the  frozen  regions  of  the  North,  will  register  about  38°  C.  The 
temperature  of  the  surface  of  his  body  varies  with  that  of  the  air 
— a  fact  with  which  all  are  familiar — but  the  internal  temperature 
is  the  same  irrespective  of  whether  it  is  winter  or  summer.  What 
is  true  of  man  is  true  also  of  other  mammals  and  of  birds — that  is, 
of  those  animals  commonly  denominated  warm-blooded. 

Poikilothermal  animals  are  animals  of  varying  heat,  or  those 
whose  temperature  varies  according  to  that  of  the  medium — air  or 
water — in  which  they  live.  The  frog's  temperature  is  slightly 
above  that  of  the  water,  and  if  this  is  warm,  the  temperature  in 
the  frog  will  rise,  to  fall  again  when  the  temperature  of  the  water 
is  lowered.  Thus  a  frog  with  a  temperature  of  20.7°  C.  in  water 
at  20.6°  C.  will  have  a  temperature  of  38°  C.  when  that  of  the 
water  is  raised  to  41°  C.  Fishes,  reptiles,  amphibia,  and  insects 
also  exhibit  this  same  variation  of  temperature,  so  that  cold- 
blooded and  poikilothermal  are  practically  interchangeable  terms. 
A  study  of  insects  shows  that  these  creatures  produce  heat,  the 
thermometer  registering,  in  some  experiments  on  butterflies  in 
active  motion,  a  temperature  of  5  degrees  C.  above  that  of  the  air. 
These  insects  are  poikilothermal.  The  same  power  of  generating 
heat  is  observed  also  in  plants.  The  amount  of  heat  varies  under 
different  circumstances,  being  especially  marked  at  the  time  of 
germination  and  flowering,  sometimes  from  5  degrees  to  10  degrees 
C.  above  that  of  the  air. 

Temperatures  of  Different  Animals. — The  following 
table  gives  the  temperatures  of  some  of  the  more  common  animals  : 

Poikilothermal  animals. 

Temperature  above 
surrounding  medium. 

.  0.32-  2.44  degrees  C. 
.  2.50-12.0  degrees  C. 
.0.50-  3.0  degrees  C. 


Temperature  of  Different  Parts  of  the  Human  Body. 

— The  temperature  of  the  skin  at  the  middle  of  the  upper  arm  is 
35.4°  C.,  while  in  the  sole  of  the  foot  it  is  but  32.26°  C.     In  the 


Mammals. 

Birds. 

Poi 

Centigrade. 

Centigrade. 

Sheep    . 
Ape 
Dog  .    . 
Horse    . 
Ox     .    . 

37.3°-40.5° 
35.5°-39.7° 
37.4°-39.6° 

3f>.8°-37.5° 
37.5° 

Duck  .    .    .  42.5°-43.9° 

Turkey  .    .  42.7° 
Chicken     .  43.0° 

Frog  . 
Snakes 
Fish    . 

408  VITAL  HEAT. 

axilla  it  is  about  37.1°  C.,  although  some  observers  have  placed  it  as 
low  as  36.25°  C.,  and  others  as  high  as  37.5°  C. ;  under  the  tongue, 
about  37.5°  C. ;  and  in  the  rectum  about  38°  C.  The  temperature  of 
the  liver,  about  41.39°  C.  in  the  sheep,  is  regarded  as  the  highest 
in  the  body  :  and  higher  here  during  digestion  than  in  the  inter- 
vals. The  mean  temperature  of  the  blood  may  be  stated  as  39° 
C.  The  temperature  of  the  muscles  is  increased  in  contraction 
1  degree  C.  Mental  exertion  also  increases  the  production  of 
heat.  After  such  exertion  the  temperature  of  the  body  has  been 
found  to  be  0.3  degree  C.  higher  than  before. 

Temperature  at  Different  Ages. — The  temperature  of  the 
child  just  born  is  37.86°  C.  (rectum) ;  in  twenty-four  hours,  37.45° 
C.  (rectum).  From  five  to  nine  years  of  age  it  is  37.72°  C.  (rec- 
tum); from  twenty-five  to  thirty,  36.91°  C.  (axilla);  from  fifty-one 
to  sixty,  36.83°  C.  (axilla);  and  at  eighty,  37.46°  C.  (mouth).  The 
amount  of  heat  produced  in  old  people  is  less  than  that  in  the  mid- 
dle-aged, and  they  therefore  need  greater  protection  from  the  cold. 

Daily  Variations  in  Temperature. — The  temperature  of  an 
individual  is  not  the  same  at  all  times  of  the  day.  His  lowest 
temperature  is  between  2  and  6  o'clock  A.  M.;  it  rises  during  the 
day,  and  at  about  4  to  8  P.  M.  is  at  its  height,  falling  again  until 
it  reaches  the  minimum  in  the  early  morning.  Thus,  in  one  set  of 
observations,  at  5  A.  M.  the  thermometer  registered  36.6°  C.;  at 
8  P.  M.  37.7°  C.;  and  at  2  A.  M.  the  following  day,  36.7°  C.,  and, 
as  shown  by  recent  experiments  of  Benedict,  a  chart  representing 
these  variations  undergoes  but  slight  changes  under  varying  con- 
ditions, the  temperature  reaching  the  minimum  at  2  to  6  A.  M.,  "  in- 
dependent of  whether  the  subject  is  sleeping  soundly  and  in  the 
recumbent  position,  or  whether  he  is  awake  and  sitting,  or  even 
standing  and  walking."  In  these  experiments  no  tendency  to  an  in- 
version of  the  temperature-curve  by  inverting  the  daily  routine  of 
life  was  observed.  If  the  temperature  is  taken  every  hour  during 
a  day,  the  mean  of  the  readings  is  called  the  "  daily  mean,"  and  is 
about  37.13°  C.  in  the  rectum. 

Remarkable  Instances  of  High  and  I/ow  Tempera- 
ture.— The  lowest  temperature  which  the  writer  has  been  able  to 
find  was  24°  C.  This  was  in  a  drunken  person  who  recovered 
from  his  debauch.  A  case  of  myxedema  is  reported  in  the  Lon- 
don Lancet  in  which,  on  the  day  previous  to  death,  the  tempera- 
ture varied  from  19°  C.  to  25°  C.  In  the  same  journal  is  recorded 
a  case  of  shock  produced  by  a  fall  on  the  spine,  in  which  the  tem- 
perature fluctuated  between  47°  C.  and  50°  C.,  and  for  seven 
weeks  did  not  fall  below  42°  C. 

The  following  case,  recorded  in  the  Brooklyn  Medical  Journal, 
illustrates  the  remarkable  variations  of  temperature  which  may 
take  place  in  a  few  hours.  The  patient  was  a  man  aged  forty- 
eight  ;  the  diagnosis  of  the  case  was  intermittent  fever.  He  had 
been  treated  two  or  three  months  before  for  delirium  tremens. 


SOURCES  OF  VITAL  HEAT.  409 

He  left  the  hospital,  became  partially  paralyzed,  and  then  devel- 
oped fever,  his  temperature  rising  to  42°  and  45°  C.;  May  1,  at 
night,  it  was  44°  C.;  May  2,  in  the  morning,  37°  C.;  May  4,  2  A.  M., 
44°  C.  He  had  chills,  and  was  treated  for  malaria.  After  May  17, 
he  had  no  rise  of  temperature.  He  was  a  wreck  from  alcohol. 

Heat-unit. — The  standard  of  measure  of  heat  is  the  heat-unit 
or  calorie.  It  is  the  amount  necessary  to  raise  the  temperature  of 
1  gram  of  water  1°  C.  This  is  called  the  small  calorie,  to  distin- 
guish it  from  the  kilocalorie  or  kilogramdegree,  which  is  equal  to 
1000  small  calories,  and  represents  the  amount  of  heat  necessary 
to  raise  the  temperature  of  1  kilogram  (liter)  1  degree  C.  It  is 
estimated  that  an  average  man  produces  daily  from  2200  to  3000 
kilocalories,  which  is  about  100  kilocalories  per  hour.  During 
active  exercise  this  amount  is  greatly  increased,  even  to  the  amount 
of  3000  kilocalories  hourly,  while  during  sleep  it  may  be  but  40 
kilocalories. 

Sources  of  Vital  Heat. — The  sources  from  which  the  heat 
of  the  body  is  derived  are  numerous.  Among  them  are  : 

1.  The  Oxidation  of  the  Food-stuffs. — The  oxidation  of  carbohy- 
drates and  fats  results  in  the  production  of  CO2  by  the  oxidation  of 
the  carbon,  and  of  H2O  by  that  of  the  hydrogen  ;  while  from  the 
proteids  are  formed  by  the  same  process  CO2,  H2O,  urea,  and  certain 
extractives.  This  oxidation  may  take  place  with  the  result  of  pro- 
ducing heat,  or  it  may  result  in  the  production  of  some  other  form 
of  energy,  as  the  contraction  of  muscles  ;  but  whatever  form  it  may 
take,  the  ultimate  products  of  oxidation  are  the  same.  Fat  burned 
outside  the  body  and  fat  burned  (oxidized)  inside  the  body  will 
produce  the  same  amount  of  heat.  If,  therefore,  the  chemical 
composition  of  the  food-stuffs  is  known,  and  also  that  of  the 
products  of  their  oxidation  when  eliminated  from  the  body,  it  is  a 
simple  matter  to  calculate  the  heat-value  of  any  food.  Chemists 
have  ascertained  that  the  oxidation  of  1  Gm.  of  carbon  to  CO2 
produces  8080  calories ;  and  of  the  same  amount  of  hydrogen  to 
H2O,  34,460  calories.  The  oxidation  of  1  gram  of  carbohydrate, 
as  starch,  to  CO2  and  H2O  results  in  the  production  of  41 16  calories, 
and  of  fat,  9312  calories.  Carbohydrates  and  fats  are  completely 
oxidized  in  the  body,  not  with  the  direct  and  immediate  production 
of  CO2  and  H2O ;  but  though  there  are  many  intermediate  stages, 
still  the  ultimate  results  are  the  same  as  when  the  oxidation  takes 
place  outside  the  body. 

Proteids,  on  the  other  hand,  are  not  completely  oxidized  in  the 
body,  for,  as  we  have  seen,  the  products  of  their  oxidation  are 
mainly  CO2,  H2O,  and  urea ;  but  urea  is  still  further  oxidizable. 
This  oxidation  does  not  occur  in  the  body,  as  urea  is  eliminated 
as  such ;  hence  in  estimating  the  heat-value  of  proteids  we  must 
deduct  that  of  urea.  The  complete  oxidation  of  1  gram  of  proteid 
to  CO2  and  H2O  produces  5778  calories,  but  we  must  deduct  from 
this  the  heat- value  of  the  urea  produced  in  their  oxidation.  One 


410  VITAL  HEAT. 

gram  of  urea  oxidized  gives  2523  calories;  the  oxidation  of  1 
gram  of  proteid  produces  ^  gram  of  urea  ;  hence  from  the  5778 
calories  produced  by  the  complete  oxidation  of  the  proteid  we  must 
deduct  841  calories,  which  gives  4937  calories  as  the  actual  heat- 
value  of  1  gram  of  proteid. 

If  now  we  recall  the  adequate  diet  of  Moleschott  (p.  130),  we 
shall  find  that  the  amount  of  heat-production  in  twenty-four  hours 
with  such  a  diet  is  2,801,148  calories,  calculated  as  follows  : 

Grams.  Calories.  Calories. 

Proteids 120  x  4937      =  592,440 

Fats      90  x  9312      =  838,080 

Carbohydrates 333  x  4116     =  1,370,628 

2,801,148 

It  must  not  be  inferred  from  the  above  statement  that  all  the 
food  taken  into  the  body  is  oxidized  and  reappears  in  the  form 
of  energy,  for,  as  we  have  seen,  a  not  inconsiderable  part  passes 
out  from  the  body  without  having  undergone  the  digestive  process. 

Although  oxidation  is  the  great  source  of  the  heat  produced  in 
the  body,  there  are  doubtless  contributory  causes,  such  as  (2)  the 
various  movements  which  take  place,  producing  heat  by  friction  ; 
also  (3)  electricity  generated  in  muscles  and  nerves ;  but  of  the 
amount  produced!  by  these  and  other  physical  causes  we  know 
but  little. 

Channels  through  which  Vital  Heat  is  I/ost.— Helm- 
holtz  estimates  that  7  per  cent,  of  the  total  heat  produced  in  the 
body  is  expended  in  the  form  of  mechanical  work ;  that  78  per 
cent,  is  discharged  through  the  skin  by  evaporation  and  radia- 
tion ;  and  15  per  cent,  by  the  lungs,  urine,  and  feces. 

Vierordt  calculates  that  the  heat  discharged  from  the  body  is 
distributed  as  follows : 

Calories. 

1.8  per  cent,  in  urine  and  feces  =         47,500 

3.5  per  cent,  in  expired  air  =         84,500 

7.2  percent,  in  evaporation  of  water  from  lungs    .     =       182,120 

14.5  per  cent,  in  evaporation  of  water  from  skin  =       364,120 

73.0  per  cent,  in  radiation  and  conduction  from  skin    --=    1,791,820 

2,470,060 

Calorimetry. — A  calorimeter  is  an  apparatus  for  determining 
the  amount  of  heat  dissipated  or  disengaged  from  any  substance 
or  from  a  living  animal.  Those  used  for  animals  consist  of  a 
chamber  adapted  to  hold  the  animal,  surrounded  by  some  medium 
which  will  absorb  the  heat,  such  as  ice,  air,  or  water. 

Dulong's  Calorimeter  consists  of  a  chamber  in  which  the  animal 
is  placed ;  this  is  contained  in  a  larger  chamber  holding  water. 
Outside  of  this  is  a  layer  of  some  non-conducting  material,  like 
wool,  and  outside  of  all  is  a  box.  Air  from  a  gasometer  is  ad- 
mitted on  one  side,  and  the  expired  air  passes  out  on  the  other. 

Reichert's  water  calorimeter  (Fig.  229)  is  described  by  its  in- 


CALORIMETRY. 


411 


ventor  as  consisting  of  "two  concentric  boxes  of  sheet  metal  which 
are  fastened  together  so  that  there  is  a  space  of  about  1J  inches 
between  them,  filled  with  water.  The  water  box  is  15  inches  in 
height  and  width,  and  18  inches  in  length.  An  opening  (h)  9 
inches  in  diameter  is  made  in  one  end  for  the  entrance  and  exit  of 
the  animal.  It  is  also  perforated  with  three  small  holes  in  the 
top  corners,  and  a  slit-like  opening  in  the  top  on  one  side.  Two 
of  the  holes  are  for  the  tubes  for  the  entrance  and  exit  of  air  (JEN9 
EX\  the  entrance  tube  being  carried  close  to  the  bottom,  while 
the  exit  tube  extends  only  to  the  top  of  the  box,  and  is  placed  in 
the  opposite  diagonal  corner,  thus  ensuring  adequate  ventilation. 
In  the  third  hole  a  thermometer  (CT)  is  inserted,  by  means  of 
which  the  temperature  of  the  calorimeter  (jacket  of  metal  and 
water)  is  obtained.  The  opening  in  the  side  is  for  the  insertion 
of  a  stirrer  ($),  which  is  for  the  purpose  of  thoroughly  mixing  the 


EXT 


FIG.  229. — Reichert's  water  calorimeter. 

water  and  thus  equalizing  the  temperature  of  both  water  and 
metal — in  other  words,  of  the  calorimeter." 

Before  using  the  apparatus  to  determine  the  heat  dissipated  by 
an  animal,  the  calorimetric  equivalent  is  determined — i.  e.,  the  amount 
of  heat  necessary  to  raise  the  temperature  of  the  calorimeter  1 
degree  C.  One  gram  of  alcohol  burned  produces  9000  calories  of 
heat.  If  the  burning  of  10  grams  raises  the  temperature  of  the 
calorimeter  1  degree  C.,  then  the  calorimetric  equivalent  will  be 


412 


VITAL  HEAT. 


90,000  calories  or  90  ktlogramdeyrees — i.  6.,  for  each  degree  of 
increase  in  the  temperature  of  the  apparatus  90  kilogramdegrees 
are  absorbed. 

Besides  the  heat  which  is  absorbed  by  the  calorimeter,  addi- 
tional amounts  are  given  off  by  the  subject  of  the  experiment  in 
its  expired  air,  and  expended  in  evaporation  of  the  water  from  its 
lungs  and  skin.  To  ascertain  these,  the  amount  of  air  supplied 
and  its  temperature  on  entering  and  leaving  the  instrument  must 
be  determined,  also  the  amount  of  water  in  the  air. 

Air  calorimeters  are  also  used,  such  as  that  of  Haldane,  Hale 
White,  and  Washbourn  (Fig.  230).  In  this  instrument  the  animal 
is  placed  in  the  chamber  C,  and  hydrogen  is  burnt  in  H.  The 
tubes  A  A  and  A' A'  being  closed,  the  heat  dissipated  by  the 
animal  expands  the  air  in  the  air-space  between  the  walls  of  the 
chamber,  and  increases  the  pressure  on  that  side  of  the  fluid  in 
the  manometer  M,  causing  it  to  move  toward  H.  The  flame  of 
hydrogen  is  regulated  so  that  the  amount  of  heat  which  is  pro- 
duced by  its  combustion  counterbalances  that  of  the  animal  and 
keeps  the  fluid  in  the  manometer  stationary.  From  the  amount  of 
water  produced  the  amount  of  hydrogen  burnt  is  calculated,  and 


FIG.  230.— Diagram  of  air  calorimeter :  F,  layer  of  felt ;  A,  tubes  for  ventilation  -r 
V,  cage;  H,  hydrogen  flame  ;  M,  manometer  (Haldane,  Hale  White,  and  Washbourn). 

the  number  of  calories  produced  by  its  burning  is  determined, 
which  equals  that  given  off  from  the  animal. 

Although  there  are  produced  in  the  adult  human  body  between 
2000  and  3000  kilocalories  of  heat  daily  (p.  409),  still  this  is  very 
materially  affected  by  various  conditions.  Thus,  children  produce 
proportionately  more  than  adults ;  strong,  than  weak  persons ; 
fleshy  persons,  than  those  who  are  thin. 

Diet  is  another  very  important  factor,  as  shown  by  the  follow- 
ing table  (Danilewsky),  giving  the  amount  of  heat  produced  under 
different  diets : 

On  a  minimum  diet 1800  kilogramdegrees. 

On  a  reduced  diet  (absolute  rest)      ....  1989 

On  a  non-nitrogenous  diet 2480 

On  a  mixed  diet  (moderate  work)  ....  3210 

On  an  abundant  diet  (hard  work)    ....  3646 

On  an  abundant  diet  (very  laborious  work)  3780 


PERSPIRATORY  GLANDS.  413 

Regulation  of  Temperature.— When  the  temperature  of 
the  muscles  is  raised  to  49°  C.  they  lose  their  contractility.  This 
figure  has  been  regarded  as  the  highest  that  can  be  reached  by  a 
living  human  being ;  indeed,  much  below  this,  45°  C.,  has  long 
been  considered  as  fatal,  although  a  temperature  of  nearly  52°  C. 
has  been  recorded.  When  the  temperature  falls  to  19°  C.  a  fatal 
result  will  follow. 

To  prevent  the  body  from  becoming  too  hot  is  one  of  the 
functions  of  the  skin.  This  it  accomplishes  by  radiation,  con- 
duction, and  evaporation.  Of  the  total  heat  given  off  from  the 
body,  73  per  cent,  is  by  radiation  and  conduction  from  the  skin, 
and*  14.5  per  cent,  is  by  evaporation.  Thus  there  is  carried  off  by 
the  skin  nearly  88  per  cent,  of  the  total  heat.  This  topic  will  again 
be  discussed  in  the  consideration  of  the  skin  and  its  functions. 

The  prevention  of  the  reduction  of  the  temperature  of  the 
body  to  an  extent  that  would  be  harmful  is  accomplished  by  wear- 
ing proper  clothing,  by  the  ingestion  of  food,  both  solid  and 
liquid,  by  warming  the  air  which  comes  in  contact  with  the  body, 
and  by  increased  muscular  activity.  The  use  of  alcohol  for  this 
purpose  is,  as  previously  stated,  delusive. 

THE  SKIN. 

The  skin  is  composed  of  a  deep  portion,  the  corium,  derma,  or 
true  skin  ;  and  of  a  superficial  portion,  the  epidermis  or  cuticle. 

Corium. — The  corium  makes  up  by  far  the  greater  part  of 
the  skin,  and  within  it  are  the  perspiratory  glands,  the  sebaceous 
glands,  the  hairs,  together  with  both  blood-  and  lymphatic  vessels. 
The  upper  surface,  where  it  joins  the  epidermis,  is  irregular, 
being  composed  of  elevations — papillae — and  intervening  depres- 
sions. In  some  of  these  papillae  are  the  tactile  corpuscles,  in  which 
nerve-fibers  end. 

Epidermis. — The  epidermis  is  made  up  of  a  deep  and  a 
superficial  layer.  The  deep  layer  (rete  mucosum  or  rete  Malpighii) 
covers  the  papillae  of  the  corium  and  fills  the  depressions  between 
them.  It  is  composed  of  cells,  round  or  of  different  shapes  due  to 
pressure  of  contiguous  cells,  the  material  of  which  they  are  com- 
posed yielding  readily.  It  is  in  this  layer  that  the  pigment  is 
deposited  which  characterizes  the  dark  races.  The  superficial 
layer  of  the  epidermis  is  composed  of  cells  which  are  flat  and 
dry  or  horny. 

Perspiratory  Glands. — The  perspiratory  glands,  also  de- 
scribed as  sweat-  and  sudoriparous  glands,  are  very  numerous,  it 
being  estimated  that  in  the  entire  skin  there  are  not  less  than 
2,400,000.  They  are  more  abundant  in  some  parts  of  the  body 
than  in  others  :  in  the  palm  of  the  hand  there  are  42  to  the  square 
centimeter;  on  the  forehead,  190;  and  on  the  cheek,,  85.  If  all 


414 


THE  SKIN. 


these  glands  in  the  body  were  straightened  out  and  put  end  to 
end,  they  would  extend  a  distance  of  4  kilometers. 

This  brief  consideration  of  the  perspiratory  glands  suggests 
that  their  function  must  be  very  important.  They  are  constantly 
at  work  pouring  out  their  secretion  upon  the  surface  of  the  skin. 
Ordinarily  this  secretion  is  not  perceptible,  and  it  is  then  called 
u  insensible  perspiration."  Upon  active  exercise  or  when  the 
temperature  of  the  air  is  high  this  secretion  becomes  visible,  and 
it  is  then  called  "  sweat "  or  "  perspiration."  The  average  total 
amount  daily  formed  is  900  grams.  This  amount  is  subject  to 


FIG.  231. — Vertical  section  of  the  skin,  diagrammatic  (after  Heitzmann). 

considerable  variations,  being  increased  in  summer  and  diminished 
in  winter.  During  violent  exercise  the  amount  may  be  as  much 
as  380  grams  per  hour,  and  during  exposure  to  very  high  tempera- 
tures it  has  been  known  to  reach  1814  grams  in  the  same  time. 

Sweat  has  a  salty  taste,  a  specific  gravity  of  1003  to  1005,  and 
is  acid  in  reaction.  It  is  claimed  by  some  writers  that  its  true 
reaction  is  alkaline,  and  that  its  acidity  is  in  reality  due  to  the 


PERSPIRATORY  GLANDS. 


415 


presence  of  fatty  acids  resulting  from  the  decomposition  of  the 
sebum.     In  uremia  the  amount  of  urea  may  be  so  great  as  to 
crystallize  on  the  skin ;  in  diabetes  sugar  may  be  found  in  the 
sweat ;  and  in  cases  of  gout  uric  acid  has  been  detected. 
The  following  table  shows  the  composition  of  sweat : 

Water. 99.00  per  cent. 

Urea 0.15       " 

Neutral  fats,  fatty  acids,   cholesterin,  sodium  and 

potassium  chlorids,  and  other  salts    .    .    .  0.85       " 

100.00 

Office  of  Perspiration. — One  of  the  important  means  of  regulat- 
ing the  temperature  of  the  body  is  the  perspiration.     Without  it, 


FIG.  232.— c,  Corneous  (horny)  layer ;  g,  granular  layer;  m,  mucous  layer  (rete 
Malpighii).  The  stratum  lucidum  is  the  layer  just  above  the  granular  layer. 
.Nerve-terminations :  n,  afferent  nerve ;  b,  terminal  nerve-bulbs ;  I,  cell  of  Lang- 
erhans  (after  Ranvier). 

exposure  to  high  temperatures  would  be  injurious,  and  in  some 
cases  would  even  be  fatal.  An  external  temperature  of  52°  C.  is 
not  infrequently  met  with  in  the  southern  part  of  the  United  States  ; 
to  this  heat  human  beings  are  exposed  without  suffering  from  its 
effects.  The  evaporation  of  the  perspiration  abstracts  heat  from 
the  body.  Of  the  heat  given  off  from  the  body,  88  per  cent, 
passes  off  by  the  skin ;  of  this  amount,  73  per  cent,  is  by  radia- 
tion and  conduction,  and  14.5  per  cent,  by  evaporation. 


416 


THE  SKIN. 


Sebaceous  Glands. — The  sebaceous  glands  are  racemose 
glands,  and  discharge  their  product — sebum — into  the  hair-folli- 
cles of  large  hairs,  as  upon  the  scalp,  while  in  other  portions  of 
the  body,  as  the  forehead,  where  the  hairs  are  small,  the  hair  pro- 
jects from  the  mouth  of  the  sebaceous  gland,  and  is  more  like  an 
appendage  than  a  separate  structure. 


C-. 


FIG.  233.— (7,  Epidermis;  D,  corium;  P,  papillae;  8,  sweat-gland  duct;  v,  arterial 
and  venous  capillaries  (superficial  or  papillary  plexus)  of  the  papillae  (deep  plexus 
is  partly  shown  at  lower  margin  of  the  diagram) ;  vs,  an  intermediate  plexus,  an 
outgrowth  from  the  deep  plexus,  supplying  sweat-glands  and  giving  a  loop  to  hair- 
papilla  (after  Eanvier). 

Composition  of  Sebum. — The  sebum,  or  sebaceous  matter,  is  of 
an  oily  nature.  It  contains  albumin,  fat,  and  cholesterin.  The 
vernix  caseosa  which  covers  the  infant  during  the  latter  part  of 
fetal  life  is  of  the  same  character,  consisting  principally  of  fat 
with  epithelium.  At  the  temperature  of  the  body  the  sebum  is 
fluid,  but  it  solidifies  on  the  surface  of  the  skin.  Its  office  is 


HAIRS  AND  NAILS. 


417 


mainly  to  keep  the  skin  and  the  hairs  soft  and  pliable.  Besides 
this,  it  is  probably  excrementitious  to  a  certain  extent. 

Cerumen,  commonly  called  "  ear-wax,"  is  the  product  of  the 
sebaceous  and  perspiratory  glands  of  the  external  auditory  meatus, 
and  is  composed  principally  of  fat  with  some  soap.  It  is  a 
reddish  substance  having  a  sweetish-bitter  taste. 

Hairs  and  Nails. — These  structures  are  modified  epidermis. 
The  hair  grows  from  the  hair-papilla,  in  the  interior  of  which 


FIG.  234. — A  normal  sweat-gland, 
highly  magnified :  a,  sweat-coil,  with 
secreting  epithelial  cells;  6,  sweat-duct; 
c,  lumen  of  duct;  d,  connective-tissue 
capsule  :  e  and  /,  arterial  trunk  and 
capillaries  supplying  the  gland  (after 
Neumann). 


FIG.  235. — A  normal  sebaceous 
gland  in  connection  with  a  lanugo- 
hair ;  greatly  magnified :  a,  con- 
nective-tissue capsule ;  6,  fatty 
secretion  ;  c,  h,  fat-secreting  cells ; 
d,  root  of  a  lanugo-hair;  e,  hair-sac ; 
/,  hair  shaft ;  p,  acini  of  sebaceous 
gland  (after  Neumann). 


there  is  a  blood-vessel.  The  integrity  of  this  papilla  is  essential 
to  the  existence  of  the  hair ;  when  destroyed,  the  hair  can  never 
be  reproduced.  It  should  be  noted  that  the  hair-papillae  and  the 
papillae  already  described  in  connection  with  the  corium  are  very 
different  structures,  and  should  not  be  confounded.  It  has  been 
estimated  that  there  are,  on  an  average,  120,000  hairs  in  the  scalp. 
As  a  rule,  the  lighter  the  color  of  the  hair  the  finer  it  is ;  in  the 
female  it  is  coarser  than  in  the  male. 

27 


418  THE  SKIN. 

Functions  of  the  Skin. — The  functions  of  the  skin  are 
numerous  and  very  important. 

(1)  Protection. — The  tissues  which   lie  beneath  the  skin  are 
delicate  and  sensitive,  and  are  protected  from  injury  by  it.     The 
epidermis,  by  reason  of  its  hard  and  tough  character,  especially 
in  the  palms  of  the  hands  and  on  the  soles  of  the  feet,  is  peculiarly 
adapted  to  this  end. 

(2)  Excretion. — It  has  already  been  noted  that  by  the  skin  a 
liter  of  fluid  is  daily  eliminated  from  the  body.     In  this  fluid  are 


FIG.  236.—A,  Shaft  of  the  hair;  B,  root  of  the  hair;  C,  cuticle  of  the  hair;  D, 
medullary  substance  of  the  hair ;  E,  external  layer  of  the  hair-follicle ;  F,  middle 
layer  of  the  hair-follicle;  G,  internal  layer  of  the  hair-follicle;  H,  papilla  of  the 
hair ;  I,  external  root-sheath ;  J,  outer  layer  of  the  internal  root-sheath  :  K,  internal 
layer  of  the  internal  root-sheath  (after  Duhring). 

dissolved  materials  representing  the  waste  of  the  tissues.  There 
is  a  reciprocal  relation  between  the  skin  and  the  kidneys  :  in 
summer,  when  the  skin  is  active,  the  amount  of  fluid  passed 
off  by  the  kidneys  is  reduced,  while  in  winter,  when  the  skin  is 
inactive,  the  work  of  the  kidneys  is  much  increased.  In  diseased 
conditions  of  the  kidneys,  the  retention  in  the  blood  of  poisonous 
materials  which  are  eliminated  by  them  in  health  is  prevented  by 
causing  the  perspiratory  glands  of  the  skin  to  assume  this  function. 
(3)  Sensation. — The  skin,  especially  at  the  tips  of  the  fingers, 


CARE  OF  THE  SKIN. 


419 


is  very  sensitive,  and  gives  knowledge  of  the  consistency  of  objects, 
also  whether  they  are  rough  or  smooth,  sharp  or  dull,  etc.  This 
subject  of  general  sensibility  will  be  fully  discussed  in  connection 
with  the  Nervous  Functions. 

(4)  Respiration. — Interchanges  are  constantly'  taking  place  in 
the  skin  analogous  to  those  which  take  place  in  the  lungs,  although 
to  a  much  less  extent.  Oxygen  is  absorbed  from  the  air  by  the 
blood  in  the  cutaneous  blood-vessels,  and  at  the  same  time  carbon 
dioxid  is  given  off.  In  frogs  these  interchanges  are  much  more 
extensive  than  in  man. 


FIG.  237. — a,  A  vascular  papilla ;  b,  a  nervous  papilla ;  c,  a  blood-vessel ;  d,  a  nerve- 
fiber;  e,  a  tactile  corpuscle  (after  Biesiadecki). 

(5)  Regulation  of  temperature,  which  has  already  been  dis- 
cussed (page  415). 

Care  of  the  Skin. — That  the  skin  may  perform  its  functions 
properly  it  must  be  taken  care  of.  The  orifices  of  the  ducts  of 
the  perspiratory  and  sebaceous  glands  must  be  kept  free,  so  that 
they  may  not  become  clogged.  If  the  skin  of  an  animal  is 
covered  with  varnish,  it  speedily  dies.  This  is  not  due  to  the 
retention  of  waste-materials,  which  act  as  poisons,  but  to  the  great 
loss  of  heat,  in  the  rabbit  the  temperature  falling  to  20°  C.  Ex- 
periment has  shown  that  if  an  animal  that  has  been  varnished  is 
packed  in  cotton  and  kept  in  a  temperature  of  30°  C.,  it  will 
survive. 

Gerlach  covered  a  horse  and  a  rabbit  with  linseed  oil,  with  the 
following  results : 


420 


THE  SKIN. 


Temperature  before. 

Temperature  after. 

Animal. 

Rectal. 

Cutaneous. 

Rectal. 

Cutaneous. 

Remarks. 

Eabbit.    .    . 

39.  7°  C. 

38°  C. 

28°  C. 

26°  C. 

f  At  time  of  death,  thirty 
\      hours  after  varnishing. 

{On   the   sixth   day  after 

Horse    .    .    . 

38° 

35° 

32° 

29° 

varnishing  ;  death  oc- 

curred on  eighth  day. 

Reference  is  frequently  made  to  the  gilding  of  a  child's  body 
to  make  it  represent  an  angel  at  the  coronation  ceremonies  of  Pope 
Leo  X.,  which  resulted  in  the  speedy  death  of  the  child.  Inasmuch 
as  the  whole  human  body  has  been  covered  by  an  impermeable 
layer  for  eight  or  ten  days  without  producing  any  disturbance 
whatever,  even  in  the  body -temperature,  it  is  probable  that  there 
was  something  in  the  gilding  material  which  acted  as  a  poison. 
The  ability  of  the  human  being  to  regulate  his  temperature  ex- 
plains the  different  result  in  man  arid  in  the  horse  and  rabbit. 

The  skin  requires  both  friction  and  bathing  to  maintain  it  in  a 
physiologic  condition.  The  process  of  rubbing  removes  the  useless 
epidermic  scales  and  any  obstructions  which  tend  to  clog  the 
mouths  of  the  glands.  The  oily  nature  of  the  sebaceous  matter, 
which  is  always  present  and  which  retains  the  dust  and  dirt 
coming  in  contact  with  it,  requires  that  the  skin  be  washed  with 
water  and  soap.  But  the  soap  must  be  free  from  irritating  in- 
gredients, such  as  rancid  fat,  and  from  too  large  an  amount  of 
alkali  and  coloring-matter,  and  from  drugs  of  various  kinds.  If 
the  skin  is  diseased,  medication  by  means  of  soap  may  be  needed, 
but  it  should  be  prescribed  by  a  physician.  If  the  skin  is  not 
diseased,  medicated  soaps  are  harmful.  Old  white  Castile  soap 
meets  all  the  indications  in  health. 

Baths. — Baths  may  be  classified  as  follows : 

Cold  hath 0°  to  24°  C. 

Temperate  bath 24°  to  26°  C. 

Tepid  bath      26°  to  32°  C. 

Warm  bath 32°  to  37°  C. 

Hot  bath 37°  to  44°  C. 

As  a  rule,  hot  baths  are  relaxing,  and  should  not,  therefore,  be 
indulged  in  too  frequently ;  indeed,  in  persons  suffering  with 
disease  of  the  heart  they  may  actually  endanger  life.  The  Turkish 
bath,  taken  under  competent  medical  supervision,  is  often  of  great 
benefit,  and  many  persons  take  it  weekly,  and  even  oftener,  with 
the  effect  of  toning  up  the  system  and  making  them  more  com- 
petent to  endure  both  physical  and  mental  fatigue.  Cold  baths, 
except  for  the  very  robust,  are  also  to  be  taken  with  great  caution. 
If  afterward  there  is  reaction  and  if  the  skin  becomes  warm  and 
pink,  they  are  beneficial,  but  if  the  skin  becomes  cold  and  blue, 
they  are  injurious.  In  fact,  this  should  be  the  test  for  each  indi- 


KIDNEYS. 


421 


vidual  to  apply  to  his  own  case.  Bathing,  except  a  sponge-  or 
plunge-bath,  should  not  be  practised  when  the  vital  powers  are  low, 
as  early  in  the  morning,  nor  after  a  long  fast,  nor  should  it  be 
indulged  in  too  soon  after  eating ;  eleven  o'clock  in  the  morning 
is,  for  the  average  person,  a  proper  time  for  a  bath  of  considerable 
duration. 

THE  URINARY  APPARATUS. 

The  kidneys  (Fig.  238)  are  situated  in  the  lumbar  region  of 
the  abdominal  cavity,  one  on  each  side  of  the  spinal  column,  with 
the  upper  border  on  a  level  with  the  twelfth  dorsal,  and  the 


FIG.  238.— Longitudinal  section  through  the  kidney :  1,  cortex  ;  1',  medullary 
rays;  1",  labyrinth;  2,  medulla;  2',  papillary  portion  of  medulla;  2",  boundary 
layer  of  medulla ;  3,  transverse  section  of  tubules  in  the  boundary  layer ;  4,  fat  of 
renal  sinus;  5,  artery;  *,  transverse  medullary  rays;  A,  branch  of  renal  artery;  C, 
renal  calyx  ;  U,  ureter  (after  Tyson  and  Henle). 

lower  opposite  the  third  lumbar  vertebra.  The  dimensions  of  each 
are  approximately  :  Length,  10  cm. ;  breadth,  5  cm. ;  thickness, 
2.5  cm.  The  weight  is  from  125  to  180  grams. 

The  shape  of  the  kidney  is  like  that  of  a  bean,  the  internal 


422 


THE  URINARY  APPARATUS. 


border  being  concave  and  presenting  a  fissure — the  hilum — at 
which  the  vessels,  the  nerves,  and  the  ureter  enter  the  organ. 
When  the  kidney  is  longitudinally  cut  in  two,  it  is  seen  to  be 
made  up  of  an  external  or  cortical  portion — cortex — and  an  in- 
ternal or  medullary  portion — medulla.  The  medullary  portion  is 
made  up  of  numerous  pyramids  (those  of  Malpighi),  from  8  to  18 
in  number,  and,  dipping  down  between  them,  as  well  as  forming 

the  outer  part  of  the  kidney,  is 
the  cortical  portion.  Each  pyra- 
mid terminates  in  a  papilla  pro- 
jecting into  a  calyx,  which,  with 
the  calices  of  other  pyramids, 
forms  the  pelvis,  the  upper  dilated 
cavity  of  the  ureter. 

Tubuli  Uriniferi  (Figs.  239, 
240). — At  each  papilla  there  open 
about  20  uriniferous  tubules,  which 
can  be  traced  to  the  base  of  the 
pyramid.  Each  tubule  continues 
into  the  cortical  portion  of  the 
kidney,  where  it  is  larger  and 
becomes  convoluted,  narrowing 
again  and  entering  the  pyramid, 
in  which  it  again  becomes  straight, 
forms  a  loop,  and  re-enters  the 
cortical  portion,  again  becomes 
convoluted,  and  finally  terminates 
in  a  spherical  body,  the  Malpigh- 
ian  capsule  or  capsule  of  Bowman. 
This  complicated  structure 
may,  perhaps,  be  traced  more 
easily  in  the  opposite  direction. 
Beginning  with  the  Malpighian 
capsule  in  the  cortical  portion, 
there  is  next  the  convoluted 
tubule,  which,  as  it  passes  into 
the  medullary  portion,  becomes 
straight  and  is  known  as  the 
"descending  limb  of  Henle's 
loop."  This  bends  on  itself, 
forming  the  ascending  limb,  like- 
wise straight,  passes  back  into 

the  cortex,  becomes  convoluted,  and  enters  a  straight  collecting 
tube  which  opens  at  the  apex  of  a  pyramid. 

The  uriniferous  tubules  are  lined  with  epithelium,  which  varies 
at  different  parts  of  their  course.  The  epithelium  which  lines  the 
capsules  and  the  neck,  and  which  covers  the  glomerulus,  is  flattened, 


FIG.  239. — Diagram  of  two  urinif- 
erous tubules:  1,  Malpighian  tuft 
surrounded  by  Bowman's  capsule; 
2,  constriction  or  neck ;  3,  proximal 
convoluted  tubule ;  4,  spiral  tubule ; 

5,  descending  limb  of  Henle's  loop; 

6,  Henle's  loop ;   7  and  8,  ascending 
limb  of  Henle's  loop ;  9,  wavy  part  of 
ascending  limb  of  Henle's   loop;  10, 
irregular  tubule ;  11,  distal  convoluted 
tubule ;    12,   first    part  of   collecting 
tube ;  13  and  14,  straight  part  of  col- 
lecting tube ;    15,  excretory  duct  of 
Bellini    (Tyson    and    Brunton,   after 
Klein  and  Noble  Smith). 


PLATE  IV, 


A,  A,  right  and  left  kidneys;  B.  urinary  bladder;  C,  C,  right  and  left  ureters;  d, 

d,  renal  arteries  (Maclise). 


KIDNEYS. 


423 


and  the  cells  have  an  oval  nucleus  (Fig.  241).  This  changes  to 
a  thick  polyhedral  epithelium,  with  a  fibrillar  or  striated  structure, 
in  the  proximal  convoluted  tubule  and  spiral  tubule  of  Schachona. 
It  is  again  flat  in  the  descending  limb  of  Henle's  loop,  while  in 
the  ascending  limb  it  resembles  that  of  the  spiral  tubule.  The 
epithelium  in  the  irregular  or  zigzag  tubule  is  angular  and  markedly 


--"Artery  of 
capsule. 


Arched  collect-  - 
ing  tubule. 
.  Straight  col- 
lecting tu-  " 
bule. 

Distal  convo-  - 
luted  tu- 
bule. 

Malpighian 
corpuscle. 
Proximal  con-  t 
voluted  tu-    C, 
bule. 
Loop  of  Henle.  (~ 


Collecting 
tubule. 


Arteria  arcua- 
ta. 


Large  collect-  - 
ing  tubule. 


Glomer- 
ulus. 


arcuata. 


Papillary  duct. 


m 


FIG.  240. — Diagrammatic  scheme  of  uriniferous  tubules  and  blood-vessels  of  kidney ; 
drawn  in  part  from  the  descriptions  of  Golubew  (Bohni  and  Davidoff). 

striated  ;  in  the  second  convoluted  tube  it  is  like  that  in  the  first ;  in 
the  junctional  tubes,  flat  and  cubical ;  in  the  straight  or  collecting 
tubes,  clear  cubical  and  columnar;  and  in  the  ducts  of  Bellini, 
clear  columnar. 

The  following  table,  from  Schafer's  Essentials  of  Histology, 
exhibits  the  differences  in  the  epithelium  of  the  tubules  in  a  manner 
very  useful  for  reference  : 


424 


THE   URINARY  APPARATUS. 


Portion  of  tubule. 


Nature  of  epithelium. 


Position  of  tubule. 


Capsule 

First  convoluted  tube  . 

Spiral  tube 

Small  or  descending) 

tube  of  Henle. .  .  .  j 

Loop  of  Henle 

Larger  or  ascending  \ 

tube  of  Henle.  .  .  .  j 

Zigzag  tube 


Second  convoluted  tube 


Junctional  tube    .  .   .  . 

Straight  or  collecting) 

tube j 

Duct  of  Bellini     . 


/  Flattened,  reflected  over  glom-  ) 
1     erulus.  j 

f  Cubical,  fibrillated,  the  cells  > 
\  interlocking.  j 

Cubical,  fibrillated  (like  the  last). 

Clear  flattened  cells. 

Like  the  last. 

f  Cubical,  fibrillated,  sometimes  ) 
\  imbricated.  f 

(Cells  strongly  fibrillated;) 
<  varying  height ;  lumen  > 
(  small. 

f  Similar  to  first  convoluted 
tube,  but  cells  are  longer, 
with  larger  nuclei,  and  they 
have  a  more  refractive  as- 
pect. 

Clear,  flattened,  and  cubical  cells. 

/Clear  cubical  and  columnar) 

\    cells.  j 

Clear  columnar  cells. 


Labyrinth  of  cortex. 

Labyrinth  of  cortex. 

Medullary  ray  of  cortex. 
/  Boundary  zone    and  partly 
|     papillary  zone  of  medulla. 

Papillary  zone  of  medulla. 
/Medulla  and  medullary  ray 
I    of  cortex. 

Labyrinth  of  cortex. 


Labyrinth  of  cortex. 

f  Labyrinth  passing  to  medul- 
\     lary  ray. 

Medullary  ray  and  medulla. 
Opens  at  apex  of  papilla. 


Blood-vessels. — The  renal  artery  (Fig.  238),  which  supplies  the 
kidney,  is  a  branch  of  the  abdominal  aorta,  which  before  entering 


FIG.  241.— From  section  of  cortical  substance  of  human  kidney :  a,  epithelium 
of  Bowman's  capsule ;  6  and  d,  membrana  propria ;  c,  glomerular  epithelium ;  e, 
blood-vessels;  /,  lobe  of  the  glomerulus;  g,  commencement  of  uriniferous  tubule; 
h,  epithelium  of  the  neck ;  i,  epithelium  of  proximal  convoluted  tubule ;  X  240 
(Bohm  and  Davidoff). 


KIDNEYS.  425 

the  organ  subdivides  into  4  or  5  vessels.  It  is  from  these  vessels 
that  the  suprarenal  capsules  and  the  ureter  also  receive  their 
blood-supply.  When,  as  frequently  happens,  there  is  a  second 
artery,  it  is  called  the  inferior  renal  artery. 

The  branches  of  the  renal  artery  pass  toward  the  cortex 
and  end  as  proper  renal  arteries,  arterice  proprice  renales,  from 
which  are  given  off  the  interlobular  arteries  in  the  direction  of  the 
cortical  substance,  and  the  arteriolw  redce  toward  the  medullary 
pyramids.  From  the  interlobular  arteries  are  given  off  the  afferent 


Nuclei  of  en- 
dothelial 
cells  of  blood 
capillaries. 

Lumen  of  uri- 
niferous  tu- 
bule. 

Striated  bor- 
der. 


FIG.  242.— Section  of  proximal  convoluted  tubules  from  man ;  X  580  (Bohm  and 

Davidoff). 

vessels,  which  pierce  the  capsules  and  end  in  the  Malpighian  tufts. 
From  the  capsules  emerge  the  efferent  vessels,  which  form  a  venous 
plexus  about  the  uriniferous  tubes,  and  the  blood  ultimately 
leaves  the  kidney  by  the  renal  vein. 

Nerve-supply  of  the  Kidney. — The  nerves  of  the  kidney,  from 
15  to  20  in  number,  have  ganglia  upon  them,  and  are  from  the 
renal  plexus.  This  plexus  is  formed  from  the  solar  plexus,  semi- 
lunar  ganglion,  lesser  and  smallest  splanchnic  nerves.  So  far  as 
known,  the  nerves  are  distributed  to  the  arterioles  principally, 


426  THE   URINARY  APPARATUS. 

though  nerve-fibrils  are  described  as  ramifying  among  the  epithe- 
lium of  the  tubules. 

Function  of  the  Kidneys. — The  function  of  the  kidneys  is  to 
form  urine.  This  is  sometimes  spoken  of  as  a  secretion,  but  inas- 
much as  its  constituents  pre-exist  in  the  blood  when  that  fluid 
comes  to  the  kidneys,  and  these  organs  simply  remove  these  sub- 
stances from  the  blood,  urine  is  more  properly  an  excretion.  The 
ingredients  composing  the  urine  may,  from  a  physiologic  stand- 
point, be  divided  into  two  groups :  (1)  Water  and  some  of  the 
salts  ;  and  (2)  urea,  uric  acid,  and  allied  substances. 

The  first  group,  consisting  of  water  and  salts,  is  eliminated 
from  the  blood  while  that  fluid  is  passing  through  the  glomerulus 
within  Bowman's  capsule,  the  beginning  of  the  uriniferous  tubules  ; 
while  the  urea  group  is  excreted  while  the  blood  is  passing  through 
the  venous  plexus  surrounding  the  convoluted  portions  of  the 
tubule. 

Excretion  of  Water  and  Salts. — While  all  authorities  agree  that 
it  is  at  the  glomeruli  that  water  and  some  of  the  inorganic  salts 
are  eliminated  from  the  blood,  there  is  a  diversity  of  opinion  as  to 
the  factors  engaged  in  this  process  ;  some  regarding  it  as  a  simple 
filtration  in  which  the  glomerular  epithelium  plays  a  passive  part, 
while  others  attribute  to  these  cells  a  very  important  part  in  the 
process.  Whenever  the  renal  blood-supply  is  increased,  the 
quantity  of  urine  is  also  increased,  and  it  has  therefore  been 
assumed  that  this  increase  was  due  to  the  heightened  blood-press- 
ure within  the  glomerulus,  and  this  is  the  basis  of  the  filtration 
theory ;  but  it  has  been  pointed  out  that  under  these  circumstances 
there  is  an  increased  blood-flow  through  the  organ,  and  it  is  to 
this  that  Heidenhain  attributes  the  increased  secretion,  rather  than 
to  the  simple  increase  of  pressure  within  the  glomeruli.  This 
authority  is  one  of  the  principal  exponents  of  the  theory  that  the 
glomerular  epithelium  is  the  efficient  agent  in  the  elimination 
which  takes  place  within  Bowman's  capsule. 

Bowman,  in  1842,  advanced  the  opinion  that  "the  Malpighian 
bodies  might  be  an  apparatus  destined  to  separate  from  the  blood 
the  watery  portion "  of  the  urine.  On  the  other  hand,  he  held 
that  "  the  tubes  and  their  plexus  of  capillaries  were  probably  the 
parts  concerned  in  the  secretion  of  that  portion  of  the  urine  to 
which  its  characteristic  properties  are  due." 

In  1884  Ludwig  expressed  the  opinion  that  all  the  constituents 
of  the  urine  escape  from  the  blood  while  passing  through  the 
glomeruli,  and  that  this  separation  is  due  to  the  high  pressure 
under  which  the  blood  is  within  these  structures. 

Heidenhain  combated  the  view  of  Ludwig  on  various  grounds  : 
Among  others,  that  a  rise  of  arterial  pressure  elsewhere  in  the 
body,  as  in  the  salivary  glands,  does  not  cause  increased  transuda- 
tion  through  the  walls  of  the  blood-vessels ;  that  the  epithelium 


KIDNEYS.  427 

covering  the  glomeruli  would  offer  great  resistance  to  filtration ; 
that  if  the  renal  vein  is  ligated  and  the  pressure  within  the 
glomeruli  thereby  increased,  not  only  is  the  flow  of  urine  not  in- 
creased, but  it  is  actually  abolished;  and,  finally,  that  filtration 
will  not  explain  the  increased  flow  of  urine  when  water  and  crys- 
talloid substances  are  increased  in  the  blood.  Heidenhain,  as 
already  stated,  believes  that  the  cells  of  the  glomerular  epithelium 
act  as  secretory  cells  do  elsewhere,  and  by  the  power  which  they 
possess  as  living  cells  eliminate  water  and  inorganic  salts,  espe- 
cially sodium  chlorid,  from  the  blood. 

In  commenting  on  these  opinions,  Starling,  to  whose  admirable 
article  on  "  The  Mechanism  of  the  Secretion  of  the  Urine/7  in 
Schafer's  Text-book  of  Physiology,  we  are  much  indebted,  says : 
"  It  seems  probable  that  in  the  glomeruli  the  process  is  largely 
if  not  exclusively  physical,"  and  that  "  we  have  at  present  no  evi- 
dence that  the  cellular  covering  of  the  glomeruli  acts  otherwise  than 
passively  in  the  production  of  the  glomerular  part  of  the  secre- 
tion." He  also  refers  to  the  researches  of  Munk  and  Senator,  who 
have  reached  the  conclusion  that  water  and  part  of  the  urinary  salts, 
especially  sodium  chlorid,  are  transuded  through  the  glomeruli  iii 
direct  consequence  of  the  blood-pressure — i.  e.,  by  a  process  of  fil- 
tration, although  the  rapidity  of  the  blood-flow  is  equally  important. 
It  is  also  generally  accepted  that  when  serum-albumin,  hemo- 
globin, or  dextrose  escapes  from  the  blood  and  becomes  a  constitu- 
ent part  of  the  urine,  this  takes  place  while  the  blood  is  passing 
through  the  glomeruli. 

The  oncometer  (p.  338)  has  been  largely  used  in  connection 
with  the  various  experiments  which  have  been  conducted  to  deter- 
mine the  effects  of  increased  and  diminished  blood-pressure  on  the 
excretion  of  urine  by  the  kidney. 

Excretion  of  Urea,  Uric  Acid,  etc. — Bowman,  in  his  views  as 
to  the  manner  of  the  formation  of  urine,  expressed  the  opinion 
that  the  tubes  and  their  plexus  of  capillaries  were  probably  the 
parts  concerned  in  the  secretion  of  the  substances  forming  this 
second  group  of  urinary  constituents,  and  this  is  the  generally 
accepted  view  of  the  authorities  of  the  present  day.  It  is  also 
probably  true  that  some  water,  sodium  chlorid,  sulphates,  and 
phosphates  are  eliminated  from  the  blood  in  this  part  of  its  course 
through  the  kidney.  The  efficient  agents  in  this  elimination  are 
the  cells  lining  the  tubules,  and  especially  those  in  the  convoluted 
portions. 

Effects  of  Removal  of  the  Kidneys. — Removal  of  a  single  kidney 
for  a  diseased  condition  of  that  organ,  constituting  nephrectomy, 
is  not  an  uncommon  operation  at  the  present  day.  After  the 
operation  the  remaining  kidney  enlarges  and  performs  the  func- 
tions of  both.  Removal  of  both  kidneys  is  followed  by  a  fatal 
result. 


428  THE   URINARY  APPARATUS. 

Ureters. — From  each  kidney  passes  a  ureter,  a  tube  which 
connects  the  kidney  with  the  bladder,  and  through  which  the 
urine  is  discharged.  It  has  a  diameter  about  that  of  a  goose-quill 
and  a  length  of  about  40.6  cm.  It  has  3  coats :  External  or 
fibrous;  middle  or  muscular;  and  internal  or  mucous.  The 
muscular  tissue  is  of  the  plain  variety  and  arranged  in  2  layers: 
longitudinal  and  circular ;  a  third  layer,  also  longitudinal,  is  found 
near  the  bladder.  The  mucous  membrane  is  covered  with  transi- 
tional epithelium  (p.  34). 

When  the  ureters  reach  the  base  of  the  bladder,  they  pass  for 
about  2  cm.  between  the  muscular  and  mucous  coats,  and  then 
open  by  a  constricted  orifice  in  the  bladder. 

Function  of  the  Ureters. — The  urine  which  is  being  constantly 
formed  by  the  kidneys  passes  into  their  pelves,  and  by  peristaltic 
action  of  the  muscular  coat  of  the  ureters  is  carried  to  the  bladder, 
into  which  it  flows  intermittently.  The  actual  entrance  of  the 
urine  has  been  observed  in  a  case  of  ectopia  vesicce  in  a  boy.  This 
condition  consists  in  a  deficiency  in  the  abdominal  wall  and  in 
the  front  wall  of  the  bladder,  so  that  the  openings  of  the  ureters 


FIG.  243. — Casper's  ureter  cystoscope  :  li,  movable  lid  covering  groove  in  which 
moves  c,  the  ureteral  catheter ;  d,  handle  of  lid ;  o,  ocular  end ;  p,  prism ;  I,  lamp, 
»,  screw  for  making  and  breaking  connection  with  the  battery ;  m,  mandril. 

can  be  inspected.  In  this  case  the  flow  of  urine  into  the  blad- 
der was  intermittent,  and  about  the  same  in  amount  "for  each 
ureter. 

By  means  of  the  cystoscope  (Fig.  243)  it  has  been  determined 
that  the  peristaltic  action  of  the  ureters  is  both  intermittent  and 
alternate ;  exceptionally  it  may  be  synchronous.  At  intervals 
of  a  minute  or  more  urine  is  discharged  from  the  ureters  into  the 
bladder,  the  amount  varying;  but  averaging,  perhaps,  from  15  to 
30  drops. 

The  cause  of  this  peristaltic  contraction  is  not  definitely  deter- 
mined. Some  authorities  attribute  it  to  the  direct  stimulation  of 
the  muscular  tissue  by  the  accumulated  urine,  which  results  in  a 
wave  which  is  propagated  from  one  muscle-cell  to  another ;  while 
others  think  that  this  contractility  of  the  musculature  of  the 
r'  ureters  is  a  power  possessed  by  it  independent  of  any  direct  stim- 
ulation, either  mechanical  or  nervous.  Experiments  upon  the  rat 
have  demonstrated  that  when  the  ureter  is  cut  into  several  pieces, 
each  section  will  contract  peristaltically. 


BLADDER. 


429 


Bladder  (Fig.  244). — This  is  not  infrequently  spoken  of  as 
the  urinary  bladder,  and  when  moderately  distended  will  contain 
about  ^  liter ;  though  it  may  be  so  distended  as  to  contain  very 
much  more  than  this. 

It  has  4  coats :  peritoneal  or  serous,  muscular,  submucous,  and 
mucous.  The  muscular  coat  is  made  up  of  3  layers  of  plain 
muscular  fiber :  External  or  longitudinal,  middle  or  circular,  and 
internal,  which  is  also  longitudinal.  The  external  longitudinal 
layer  is  also  described  as  the  detrusor  urince  muscle,  and  the  aggre- 


FIG.  244.— Section  of  penis,  bladder,  etc. :  1,  symphysis  puhis ;  2,  prevesical 
space;  3,  abdominal  wall;  4,  bladder;  5,  urachus;  6,  seminal  vesicle  and  vas 
deferens ;  7,  prostate  ;  8,  plexus  of  Santorini ;  9,  sphincter  vesicse ;  10,  suspensory 
ligament  of  penis;  11,  penis  in  flaccid  condition;  12,  penis  in  state  of  erection  ;  13, 
glans  penis ;  14,  bulb  of  urethra ;  15,  cul-de-sac  of  bulb,  a,  Prostatic  urethra ;  b, 
membranous  urethra;  c,  spongy  urethra  (Testut). 

gation  of  the  fibers  of  the  circular  layer  around  the  neck  of  the 
bladder  and  the  beginning  of  the  urethra,  as  the  sphincter  vesicce. 
The  mucous  coat  or  mucous  membrane  is  covered  with  transitional 
epithelium,  and  contains  racemose  glands. 

Nerve-supply. — The  nerves  supplying  the  bladder  are,  according 
to  Langley  and  Anderson,  derived  from  (1)  the  second  to  the  fifth 
lumbar  nerves,  reaching  the  organ  through  the  sympathetic  chain, 
the  inferior  mesenteric  ganglion,  and  the  hypogastric  nerves ;  (2) 
the  second  and  third  sacral  spinal  nerves.  Stimulation  of  the 


430  THE   URINARY  APPARATUS. 

first  group  causes  feeble,  and  of  the  second  strong,  contraction  of 
the  bladder. 

Function  of  the  Bladder. — The  bladder  acts  as  a  reservoir  for 
the  urine  until  such  time  as  it  is  passed  in  the  act  of  urination  or 
micturition.  The  urine  is  retained  within  the  bladder  by  the  tonic 
contraction  of  the  sphincter  vesicse  in  the  same  manner  as  feces 
are  retained  in  the  rectum  by  the  sphincter  ani.  The  pressure  of 
the  urine  when  the  bladder  is  full  is  equal  to  only  1  cm.  of  mer- 
cury, while  it  takes  a  pressure  of  at  least  3  cm.  to  overcome  the 
elasticity  of  the  sphincter.  When  the  bladder  is  about  to  be 
emptied,  as  the  result  of  an  inhibitory  impulse,  the  sphincter  vesicse 
becomes  relaxed.  At  the  same  time  the  muscular  coat  of  the 
bladder  and  the  abdominal  muscles  contract,  and  the  urine  begins 
to  flow.  The  pressure  which  is  thus  exerted  equals  10  cm.  of 
mercury.  Although  the  starting  of  the  act  is  voluntary,  when 
once  it  has  begun  it  continues  under  the  influence  of  the  vesico- 
spinal  center  situated  in  the  lumbar  part  of  the  cord  until  the 
bladder  is  empty. 

Up  to  a  certain  point  the  brain  is  able  to  inhibit  the  center  and 
postpone  the  evacuation  of  the  bladder,  but  after  a  time,  if  too 
long  delayed,  the  resistance  of  the  sphincter  is  overcome  and  urine 
will  flow.  It  is  more  difficult  to  stop  the  act  after  it  has  once 
begun  than  to  delay  its  beginning,  for  the  urine,  flowing  over  the 
mucous  membrane  of  the  urethra,  stimulates  the  vesicospinal 
center,  and  the  efferent  impulses  to  the  contracting  muscles  are 
increased. 

If  the  mucous  membrane  of  the  bladder  is  inflamed,  as  in 
cystitis,  the  stimulation  of  the  center  may  be  so  great  as  to  pre- 
vent the  brain  from  inhibiting  the  evacuation,  and  this  may  occur 
when  only  a  small  quantity  of  urine  is  accumulated.  Or  it  may 
happen  that  the  spinal  cord  is  injured  or  diseased  in  the  upper 
or  middle  portion,  and  thus  all  sensation  caused  by  a  full  bladder 
may  be  abolished.  Under  these  circumstances  the  bladder,  when 
full,  will  be  emptied  by  the  reflex  action  of  the  vesicospinal  center. 
Or,  again,  if  the  lesion  of  the  cord  is  such  as  to  disorganize  this 
center,  then  there  will  be  no  reflex  action  of  the  cord,  and  the 
elasticity  of  the  tissues  about  the  neck  of  the  bladder  will  keep  the 
urine  in  that  viscus  until  the  elasticity  is  overcome  by  the  disten- 
tion,  when  the  urine  will  flow  in  drops  as  fast  as  it  comes  from 
the  kidneys;  but  the  bladder  will  not  empty  itself.  Inexperi- 
enced persons  are  often  deceived  by  this  dribbling  of  the  urine, 
thinking  that  its  discharge  is  evidence  that  the  bladder  is  perform- 
ing its  duty,  while  the  fact  is  that  it  is  evidence  of  paralysis  and 
retention. 

Urethra  (Fig.  244).— This  canal  extends  from  the  neck  of  the 
bladder  to  the  meatus  urinarim,  and  in  the  male  is  about  20.4  cm. 
and  in  the  female  about  3.7  cm.  in  length.  It  is  lined  with 


REACTION  OF  THE  URINE.  431 

mucous  membrane,  in  which  are  mucous  glands,  glands  of  Littre, 
and  opening  into  it  in  the  male  are  two  compound  racemose 
glands,  Cowper's  glands.  In  the  female  urethra  the  epithelium  is 
stratified.  In  the  male  urethra  it  is  stratified  near  the  meatus, 
transitional  in  the  prostatic  portion,  and  elsewhere  columnar. 

THE  URINE. 

Quantity. — The  amount  of  urine  voided  by  an  adult'  in 
twenty-four  hours  is  about  1500  c.c.,  although  it  may  vary  within 
normal  limits  from  1200  c.c.  to  1700  c.c.  In  health  the  increased 
drinking  of  fluids  and  lessened  formation  of  the  perspiration  will 
increase  the  amount  of  urine  excreted,  while  the  excretion  will  be 
diminished  if  the  quantity  of  liquids  drank  is  lessened  or  if  the 
perspiratory  glands  are  more  active.  It  is  a  matter  of  common 
observation  that  in  summer  the  urinary  flow  is  less  than  it  is  in 
winter. 

Color. — The  color  is  ordinarily  yellow,  though  it  may  be, 
even  in  health,  almost  colorless  or  reddish  brown.  The  urinary 
pigments  are  urochrome,  urobilin,  uroerythrin,  and  hematopor- 
phyrin. 

Urochrome. — This  is  the  essential  pigment  to  which  the  yellow 
color  is  due.  It  has  been  demonstrated  that  when  alcoholic  solu- 
tions of  pure  urochrome  are  treated  with  aldehyd  a  reducing 
action  is  produced  on  the  pigment  and  urobilin  is  produced.  This 
would  indicate  that  urochrome  is  an  oxidation-product  of  urobilin. 

Urobilin. — This  is  the  same  as  stercobilin  of  the  feces,  and  is 
probably  formed  from  the  bilirubin  of  the  bile.  Urobilin  exists 
in  small  amount  in  the  urine,  and  principally  in  the  form  of  a 
chromogen,  to  which  the  name  urobilinogen  has  been  given.  Uro- 
bilin and  hydrobilirubin  are  regarded  by  some  as  identical.  Hop- 
kins states  that  the  origin  of  urinary  bilirubin  is  probably  three- 
fold— from  absorption  of  the  ready-formed  pigment  in  the  bowel ; 
from  direct  production  in  the  liver  ;  and  from  reduction  of  the 
blood-pigment  in  the  organ,  independently  of  hepatic  agency. 

Uroerythrin. — This  coloring-matter  is  that  which  gives  the 
characteristic  color  to  the  pinkish  deposits  of  urates.  It  exists 
in  small  amount,  but  it  is  always  present  in  normal  urine. 

Hematoporphyrin. — Although  normally  present  in  but  small 
amount,  this  substance  may  exist  pathologically  in  considerable 
quantity. 

Reaction. — The  reaction  of  the  mixed  urine  passed  in  twenty- 
four  hours  is  acid  to  litmus,  due  to  the  presence  of  sodium  dihy- 
drogen  phosphate,  NaH2PO4,  or,  as  it  is  more  commonly  called, 
acid  sodium  phosphate. 

The  acidity  of  the  urine  is  subject  to  considerable  variation. 
It  is  increased  after  exercise  and  after  the  consumption  of  animal 


432 


THE   UEINE. 


food  ;  it  is  decreased  after  the  ingestion  of  vegetable  food,  because 
this  contains  compounds  of  organic  acids  which  by  oxidation  form 
carbonates,  and  these  latter  may  be  so  plentiful  as  to  make  the 
urine  alkaline. 

The  alkaline  tide  is  a  term  applied  to  the  condition  in  which 
during  the  period  when  hydrochloric  acid  is  being  set  free  as  a 
constituent  of  the  gastric  juice  the  urine,  through  the  elimination 
from  the  blood  of  the  bases,  becomes  less  acid  and  sometimes  even 
alkaline. 

There  is  also  a  difference  in  the  degree  of  acidity  of  the  urine 
at  different  times  of  the  day,  without  regard  to  the  food  taken. 

Specific  Gravity.—  This  varies  from  1015  to  1025,  being 
lower  when  the  quantity  of  urine  is  increased,  and  higher  when  it 
is  diminished.  It  may,  in  extreme  cases,  as  after  the  drinking  of 
large  quantities  of  fluid,  be  as  low  as  1005.  In  diseased  condi- 
tions, as  in  diabetes  mellitus,  the  quantity  is  greatly  increased  and 
this  is  accompanied  by  a  high  specific  gravity. 

Composition.  —  In  the  following  table  are  given  two  analyses 
by  Bunge  of  the  twenty-four  hours7  mixed  urine  of  a  young  man  : 
The  "meat  diet77  consisted  of  beef  with  a  little  salt  and  spring- 
water  ;  the  "  bread  diet  "  consisted  of  bread,  butter,  and  water  : 


Total  quantity  in  twenty-four  hours 
Urea  .    .    .    . 


Meat  diet. 
1672  c.c. 
67.2    rams 


Creatinin  .............  2.163 

Uric  acid      ............  1.398 

Sulphuric  acid  (total)        ......  4.674 

Phosphoric  acid      .........  3.4/37 

Lime     ..............  0.328 

Magnesia      ............  0.294 

Potash  ..............  3.308 

Soda      ..............  3.391 

Chlorin     .    .    ...........  3.817 


Bread  diet. 
1920  c.c. 
20.3  grams 

0.961 

9.253 

1.265 

1.658 

0.339 

0.139 

1.314 

3.923. 

4.996 


The  urine  of  an  adult  living  upon  an  ordinary  mixed  diet  and 
amounting  in  the  twenty  -four  hours  to  1500  c.c.  would  contain 
approximately  1440  c.c.  of  water  and  60  grams  of  solids,  of 
which  35  grams  would  be  urea. 

Urea,  CO(NH2)2.  —  Chemically  this  substance  is  an  amid  of 
carbonic  acid,  and  is  also  described  under  the  name  carbamid.  It 
is  isomeric  with  ammonium  cyanate,  (NH4)CNO,  and  was  pre- 
pared therefrom  by  Wohler  in  1828.  It  crystallizes  in  the  form 
of  colorless  needles  or  rhombic  prisms  ;  is  soluble  in  water  and 
alcohol,  but  is  insoluble  in  ether  and  chloroform. 

With  nitric  acid,  urea  becomes  urea  nitrate,  CO(NH2)2NO2OH, 
which  forms  in  its  crystallization  rhombic  tables;  the  angles  of 
these  are  usually  cut  off,  making  six-sided  crystals,  which  fre- 
quently overlap  one  another.  The  formation  of  these  crystals  is 
used  as  a  test  for  urea. 


COMPOSITION  OF  THE  URINE.  433 

With  oxalic  acid  urea  forms  urea  oxalate,  CO(NH2)2(COOH)a 
which  crystallizes  as  short  rhombic  prisms. 

Urea  is  converted  into  ammonium  carbonate  by  the  action  of 
the  ferment  Micrococcus  urece;  this  change  which  takes  place  in 
urine  declares  itself  by  the  ammoniacal  odor  which  is  developed. 
It  is  represented  by  the  following  equation  : 

CO(NH2)2      +      2H20      =     (NH4)2C03 

Urea.  Water.  Ammonium  carbonate. 

Urea  is  the  end-product  of  the  proteid  metabolism  of  the  body 
and  of  the  albuminoids  of  the  food.  When  a  meal  containing 
considerable  proteids  has  been  ingested,  and  the  urea  determined, 
the  amount  will  be  at  a  maximum  at  the  third  or  fourth  hour  ; 
this  is  supposed  to  indicate  the  absorption  of  peptones  from  the 
stomach.  A  second  maximum  occurs  at  the  sixth  or  seventh  hour, 
and  this  is  attributed  to  the  absorption  of  peptones  from  the 
intestine. 

Formation  of  Urea.  —  Urea  exists  in  the  blood  when  that  fluid 
reaches  the  kidney,  and  the  function  of  this  organ  is,  so  far  as 
urea  is  concerned,  simply  to  eliminate  it.  Without  recounting 
the  experimental  evidence,  which  is  ample  and  satisfactory,  it  is 
enough  to  say  that  urea  is  formed  by  the  cells  of  the  liver.  The 
most  satisfactory  explanation  of  the  manner  of  this  formation  is 
that  given  by  Dreehsel,  and  is  substantially  as  follows  :  Proteids 
undergo  hydrolytic  cleavage,  and  leucin,  tyrosin,  aspartic  acid,  and 
other  amido-bodies  are  formed  :  these  undergo  oxidation,  forming 
NH3,  CO2,  and  H2O  ;  NH3  and  CO2  unite  to  form  ammonium 

NH 
carbonate,  CO<AJJ  ,    which,    by  the   loss   of  a   molecule   of 


water,  brought  about  by  the  liver-cells,  becomes  urea  : 


Ammonium  carbonate.  Water.  Urea. 

DrechsePs  view  is  that  this  is  accomplished  in  two  stages  : 
First,  two  atoms  of  hydrogen  are  removed,  and  then  one  atom  of 
oxygen. 

A  series  of  experiments  by  various  physiologists  have  demon- 
strated that  when  the  liver  is  removed  from  dogs,  although  this 
operation  is  ultimately  fatal,  carbonates  appear  in  the  urine  and 
there  is  a  diminished  amount  of  urea.  That  any  urea  is  found 
demonstrates  that  the  liver  is  not  its  only  source  ;  but  where  else 
it  is  formed  is  not  known. 

Uric  Acid  (C5N4H/)3).  —  The  amount  of  this  substance  in  human 
urine  is  very  small,  being  on  an  average  about  0.8  gram,  but  it  is 
the  principal  nitrogenous  constituent  of  the  urine  of  birds  and 

28 


434  THE  URINE. 

reptiles,  and  is  the  end-product  of  their  proteid  metabolism,  as 
urea  is  that  of  mammals.  When  pure  it  crystallizes  in  the  form 
of  small  rhombic  crystals,  which  vary  much  in  shape  when  de- 
posited from  the  urine,  and  this  is  said  to  depend  upon  the  nature 
of  the  pigment  with  which  they  are  associated. 

Uric  acid  is  soluble  in  cold  water  to  the  extent  of  but  1  part 
in  15,000 ;  1  liter  of  boiling  water  will  dissolve  ^  gram.  It 
is  soluble  in  sulphuric  acid,  but  insoluble  in  ether  and  alcohol. 

The  presence  of  uric  acid  is  recognized  by  means  of  the 
murex id-test,  or,  as  it  is  sometimes  called,  WeidePs  reaction.  It 
is  applied  as  follows,  the  method  being  that  recommended  by 
Hopkins,  which  he  regards  as  the  most  delicate  method  of  apply- 
ing it:  If  a  small  quantity  of  uric  acid  is  placed  upon  a  watch- 
glass,  a  little  strong  nitric  acid  or  a  few  drops  of  bromin-water 
added,  and  the  whole  dried  upon  the  water-bath,  an  orange-red 
residue  is  obtained,  which,  if  touched  with  a  drop  of  ammonia, 
yields  a  fine  purple  color.  If  a  minute  quantity  of  sodium  hydrate 
solution  is  subsequently  added,  the  purple  color  changes  to  blue, 
while  on  warming  the  alkaline  solution  all  color  is  discharged. 
The  water-bath  should  always  be  used  for  evaporation  in  applying 
this  test,  and  if  the  watch-glass  is  allowed  to  remain  in  the  bath 
for  a  considerable  time  after  evaporation  is  complete,  a  red  color 
will  develop  without  further  treatment,  and  the  residue  will  dis- 
solve to  a  purple  solution  in  distilled  water.  It  is  on  account 
of  this  purple  color  that  the  test  receives  its  name.  From  the 
genus  Murex  were  obtained  various  colors  ;  two  of  these  mollusks, 
Murex  brandaris  and  Murex  truneuhis,  yielded  a  secretion  which, 
when  exposed  to  the  air,  became  purple.  The  celebrated  Tyrian 
purple  was  obtained  from  these  gastropods. 

Uric  acid  is  dibasic,  and  there  are  formed  by  it  three  forms  of 
salts  :  Neutral  tirafeg,  which  do  not  occur  in  the  urine  ;  acid  urates 
or  b i urates  ;  and  quadriurates. 

As  already  stated,  uric  acid  does  not  exist  free  in  urine — ?.  f.T 
in  recently  passed  urine  ;  though  after  standing  and  being  cooled 
uric  acid  is  deposited  as  such.  The  deposit  of  uric  acid  which 
ordinarily  occurs  is  that  known  as  brick-dust  or  fatcritious  deposit, 
and  consists  of  urates  in  an  amorphous  condition.  Although  these 
are  usually  regarded  as  biurates,  Roberts  considers  them  to  be 
quad  ri  urates. 

Sources  of  Uric  Acid. — In  a  paper  concerning  the  sources  of  uric 
acid,  published  in  the  Brooklyn  Medical  Journal  under  the  title 
44  The  Genesis  of  Uric  Acid,"  Chittenden  prefaces  his  consideration 
of  the  subject  by  emphasizing  two  vital  points : 

••  First,  the  close  chemical  relationship  of  the  purin  bases,  viz., 
adeniu,  hypoxanthin,  guanin,  xanthin,  and  the  methyl  xanthins, 
theobromin,  caffein,  etc.,  together  with  uric  acid,  which  is  likewise 


COMPOSITION  OF  THE   URISE. 


a  purin  body.     The  intimate  chemical  relationship  of  these  bodies 
is  indicated  by  the  following  structural  formulae  : 

X—  C  NH, 


HC 


HC      C—  N 

II 

N  —  C—  N 

Hypoxanthin. 

HN—  CO 

(NH,)C       C—  NH 
K_C  —  N 


C  —  N 


N—  C— 

Adenin. 


HN—  CO 
OC 


C  — 
| 
HN  —  C  — 


Guanin. 

HN—  CO 

OC      C— 

I 
HN—  C  —  N 

Xanthin. 


NH 

Uric  acid. 


X 


CO 


NH 


CH 


"  Purin,  as  has  been  shown  by  E.  Fischer,  has  the  formula  : 
N=CH 

HC    C—  NH 
N—  C—  N 

"The  purin  bases  and  uric  acid  are  derived  from  purin  by 
simple  substitution  of  the  various  hydrogen  atoms  by  hydroxyl, 
amid,  or  alkyl  groups,  as  is  plainly  evident  from  comparison  of 
the  different  formulae. 

"Secondly,  it  must  be  noted  that  all  true  nucleins  on  decompo- 
sition by  chemical  means  yield  more  or  less  of  the  above  purin 
bases,  as  was  first  pointed  out  by  Kossel.  This  means  that  all 
nucleins  contain  in  their  molecules  some  purin  bases  —  t.  e.,  in  a 
state  of  combination,  from  which  combination  they  can  be  split 
off  by  appropriate  means  either  in  the  body  or  by  chemical 
methods  outside  of  the  body.  Further,  as  these  nuclein  or  purin 
bases  stand  in  such  close  relationship  to  cell-nuclei,  it  is  easy  to 
see  how  the  quantity  of  these  substances  may  be  largely  increased 
whenever  from  any  cause  the  number  of  nucleated  cells  is  increased 
in  any  part  of  the  body.  Thus,  while  normal  blood  yields  only 
traces  of  purin  bases,  in  leukemia  the  amount  of  nuclein  bases 
may  be  increased  to  over  0.1  per  cent." 


436  THE  URINE. 

Prof.  Chittenden  concludes  his  admirable  paper  in  the  follow- 
ing" language  : 

"  In  man  uric  acid  has  a  twofold  origin ;  one  portion,  coming 
from  the  breaking  down  of  nuclein-containing  tissues  or  cell- 
elements  of  the  man's  own  body,  and  hence  is  of  endogenous 
origin,  while  the  other  portion — usually  the  larger — is  of  exogen- 
ous origin,  coming  from  the  transformation  of  free  and  combined 
purin  compounds  present  in  the  food.  The  uric  acid  of  endogen- 
ous origin  is  essentially  constant  in  amount  for  the  same  indi- 
vidual under  all  conditions  of  diet,  but  is  subject  to  slight  varia- 
tion in  connection  with  alterations  in  the  activity  of  the  tissues. 
Changed  conditions  embodying  increased  katabolism  of  the  tissue- 
elements,  increased  breaking  down  of  cells  and  cell-nuclei,  might 
naturally  be  expected  to  cause  slight  alteration  in  the  amount  of 
endogenous  uric  acid,  but  analytic  results  at  present  do  not  justify 
belief  in  any  profound  changes  in  the  uric  acid  output  due  to  this 
cause.  The  amount  of  endogenous  uric  acid  is,  therefore,  a 
physiologic  constant  for  a  given  individual,  and,  as  might  be  ex- 
pected, decided  variations  are  to  be  found  in  the  value  of  this 
constant  for  different  individuals.  In  other  words,  personal  idio- 
syncrasy, constitutional  differences,  etc.,  may  manifest  themselves 
in  the  amount  of  endogenous  uric  acid  produced.  Such  a  condition 
of  things  is  by  no  means  strange  or  out  of  harmony  with  physio- 
logic laws.  There  is  a  personality  in  every  man,  internal  as  well 
as  external,  and  the  individual  constancy  in  endogenous  uric  acid 
production  is  merely  another  illustration  of  the  general  truth  of 
this  law.  Individual  functional  peculiarities  are  as  liable  to 
existence  as  personal  peculiarities  of  form  and  structure. 

"  The  amount  of  exogenous  uric  acid  produced  in  the  body  is 
dependent  mainly  upon  two  factors,  viz.,  the  quantity  and  char- 
acter of  the  nucleins  contained  in  the  ingested  food,  and  the 
quantity  and  character  of  the  free  purin  bases  present  in  the  food. 
The  nucleins  owe  their  influence  solely  to  the  combined  purin 
bases  they  contain,  and  since  nucleins  from  different  glands  and 
tissues  differ  both  in  the  amount  and  character  of  the  purin  bases 
present  in  their  molecules,  it  follows  naturally  that  the  individual 
nuclein-containing  foods  have  different  values  as  sources  of  exogen- 
ous uric  acid.  Further,  since  all  nucleins  are  somewhat  slowly 
attacked  by  the  digestive  fluids,  it  follows  that  the  uric  acid 
coming  from  this  source  does  not  appear  at  once  in  the  urine,  but 
is  found  some  hours  after  digestion  has  been  under  way.  The  free 
purin  bases,  on  the  other  hand,  such  as  are  contained  in  meats, 
meat-juice,  meat-extracts  and  soups,  coffee,  cocoa,  etc.,  lead  to  a 
quicker  output  of  uric  acid,  owing  to  their  ready  solubility  and 
availability.  Differences  in  the  extent  of  this  form  of  exogenous 
uric  acid  production,  however,  are  traceable  to  differences  in  the 
nature  of  the  free  purin  bases ;  adenin,  hypoxanthin,  and  guanin, 


COMPOSITION  OF  THE   URINE.  437 

for  example,  showing  distinct  differences  in  the  extent  to  which 
they  are  individually  converted  into  uric  acid  in  the  body. 

"  Finally,  we  see  that  there  is  no  causal  relationship  whatever 
between  the  daily  urea  and  uric  acid  output.  They  come  from 
totally  different  lines  of  metabolism ;  they  stand  for  totally  dis- 
tinct chemico-physiologic  processes;  and  hence  any  attempt  to 
emphasize  the  so-called  ratio  of  urea  to  uric  acid  in  the  urine  is 
misleading,  and  shows,  furthermore,  a  lack  of  understanding  of 
the  true  genesis  of  these  two  excretory  products.  Between  uric 
acid  and  ordinary  proteid  metabolism  there  is  no  connection  what- 
ever. With  a  purely  non-nitrogenous  diet,  on  the  one  hand,  and 
a  diet  rich  in  eggs,  milk,  and  cheese,  on  the  other,  with  perhaps  a 
maximum  amount  of  contained  proteid,  the  output  of  uric  acid 
remains  practically  unchanged.  The  genesis  of  uric  acid  is  to  be 
found  solely  in  metabolism  of  the  tissue  nucleins  (endogenous)  and 
in  the  transformation  of  the  nucleins  and  free  purin  bases  of  the 
ingested  foods  (exogenous)." 

In  discussing  this  subject,  J.  Walker  Hall,  in  his  book,  "  The 
Purin  Bodies  of  Food  stuffs,"  etc.,  says  :  "  As  (  endogenous '  purins 
are  practically  waste-products  on  their  way  to  excretion,  so  when 
they  become  i  exogenous '  to  another  organism,  they  have  little  nu- 
tritive value  and  demand  early  and  rapid  elimination.  This  is 
generally  effected  by  the  oxidation  of  the  oxy-purins,  hypoxanthin 
and  xanthin,  to  uric  acid,  and  then  the  purin  ring  or  chain  in 
the  uric  acid  is  in  the  liver  partially  split  off  and  a  portion  of 
the  uric  acid  excreted  as  urea."  It  would  appear  from  this 
statement  that  there  is  a  certain  relationship  between  uric  acid 
and  urea,  but  this  is  quite  different  from  the  old  idea  that  a  cer- 
tain definite  ratio  exists  between  the  output  of  urea  and  uric 
acid  on  the  assumption  that  both  come  from  the  ordinary  proteid 
katabolism. 

There  is  evidence  looking  toward  the  synthetic  production  of 
uric  acid  in  the  liver,  but  this  is  not  yet  proven.  The  influence 
of  alcohol  and  alcoholic  fluids  in  the  excretion  of  uric  acid  is  dis- 
cussed elsewhere  (p.  161). 

Xanthin  Bases. — The  urine  contains  besides  xanthin,  the  follow- 
ing members  of  this  group  :  Heteroxanthin,  paraxanthin,  hypo- 
xanthin, guanin,  adenin,  and  carnin.  They  are  related  to  uric 
acid,  as  is  shown  by  the  formulae  given  on  page  435,  and  these  bases 
and  uric  acid  are  called  by  Kriiger  and  Wulff  attoxurie  substances, 
because  of  their  relation  to  alloxan  and  urea.  The  amount  of  the 
xanthin  bases  daily  excreted  in  the  urine  is  about  0.1  gram.  They 
are  increased  after  taking  green  vegetables  and  on  a  diet  contain- 
ing much  nucleins,  and  also  in  some  form  of  leukemia, 

Hippuric  Acid  (C9H9NO3). — Although  present  in  herbivora  in 
considerable  amount — 2  per  cent,  in  cattle — hippuric  acid  occurs 
in  human  urine  on  an  ordinary  diet  to  the  amount  of  but  about 


438  THE   URINE. 

% 

0.7  gram   per   diem,   being   increased    three   or   four   times   this 
amount  if  fruits  enter  largely  into  the  diet. 

Creatinin. — This  substance  exists  in  human  urine  under  a  mixed 
diet  to  the  extent  of  about  1  gram  in  the  twenty-four  hours.  Its 
principal  source  is  the  creatin  contained  in  the  meat  ingested,  as 
is  represented  by  the  following  equation  : 

C4H9N302  -  H20  =  C4H7N30 

Creatin.  Water.  Creatinin. 

It  is  possible  that  some  of  the  creatinin  in  the  urine  may  come 
from  the  creatin  of  the  muscular  tissue  of  the  body,  although 
this  is  not  established. 

Proteids. — In  the  urine  is  a  minute  quantity  of  a  nueleoproteid 
from  the  cells  lining  the  urinary  passages.  This  may  be  present 
in  sufficient  quantity  to  react  to  Heller's  test,  which  consists  in 
allowing  urine  to  flow  down  the  side  of  a  test-tube  in  which  is 
strong  nitric  acid.  The  urine  floats  on  the  acid,  and  where  the 
two  join  a  white  ring  of  coagulated  proteid  forms.  In  cystitis, 
an  inflammation  of  the  mucous  membrane  lining  the  bladder,  the 
quantity  of  the  nueleoproteid  may  be  increased,  and  this  is  precip- 
itated when  acetic  acid  is  added  to  the  urine.  The  nueleo- 
proteid of  the  urine  is  also  increased  in  leukemia. 

Albuminuria. — Under  some  circumstances  serum-albumin  and 
serum-globulin  are  found  in  the  urine,  constituting  albuminuria. 
These  doubtless  always  exist  in  minute  quantities  in  health,  but 
may  come  from  the  cells  of  the  passages  along  which  the  urine 
travels,  and  not  from  the  blood  as  it  flows  through  the  glomeruli, 
as  they  undoubtedly  do  in  true  albuminuria,  which  is  a  patho- 
logic condition. 

Peptonuria  and  Albumosuria. — These  conditions  are  character- 
ized by  the  presence  in  the  urine  of  peptones  and  albumoses, 
respectively.  We  have  already  seen  that  the  products  of  digestion, 
peptones,  are  changed  in  their  passage  through  the  gastric  and 
intestinal  walls  by  the  cells  into,  probably,  serum-albumin  and 
serum-globulin  ;  certainly,  they  do  not  enter  the  blood  as  peptones. 
If  either  wall  is  much  diseased,  as  in  cancer  of  the  stomach, 
the  peptones  and  albumoses  or  proteoses  may  not  be  changed, 
but  may  enter  the  blood  in  these  forms  and  appear  in  the  urine, 
being  eliminated  by  the  kidneys.  It  is  probably  in  the  form  of 
albumoses  or  proteases  rather  than  peptones  that  this  elimination 
takes  place.  This  condition  of  peptonuria  may  occur  in  connec- 
tion with  abscesses  or  collections  of  pus,  the  pus-cells  having 
broken  down,  and  peptone  being  one  of  the  products  which  is 
taken  up  by  the  blood  and  carried  to  the  kidneys,  where  it  is 
eliminated. 


COMPOSITION  OF  THE   URIXE.  439 

* 

Aromatic  Substances. — Hippuric  acid  or  ben zami do-acetic  acid 
belongs  to  the  aromatic  series,  by  reason  of  its  containing  the 
benzene  nucleus.  Besides  this,  there  are  other  aromatic  substances 
which  come  from  the  food  and  also  from  the  proteids  of  the  tissues. 
Among  these  are  phenol,  kresol,  pyrocatechin,  sometimes  inosit,  and 
various  carboxy 'acids.  Indoxyl,  which  is  produced  by  the  oxida- 
tion of  the  indol  that  is  absorbed  from  the  intestine,  and  skaioxyl, 
produced  in  the  same  manner  from  skatol,  also  occur  in  urine. 

Dextrose. — Ordinary  urine  contains  dextrose  to  the  amount 
of  from  0.08  to  0.18  gram  per  diem.  The  presence  of  dextrose 
in  normal  urine  has  been  and  still  is  denied,  but  the  most  recent 
investigations  seem  to  leave  no  doubt  upon  this  much  mooted 
question. 

We  have  seen  that  alimentary  glycosuria  may  occur  when 
an  excessive  amount  of  sugar  is  ingested.  In  diabetes  mellitu& 
the  quantity  of  dextrose  in  the  urine  may  be  very  great,  500 
or  600  grams  being  excreted  in  a  single  day.  The  methods  of 
recognizing  the  presence  of  dextrose  have  been  previously  referred 
to  (p.  87). 

Lactose. — The  presence  of  this  variety  of  sugar  in  the  urine 
constitutes  lactosuria,  and  this  condition  of  the  nursing  mother's 
urine  is  quite  constant.  Lactose  is  formed  by  the  mammary  gland, 
absorbed  by  the  blood,  and  eliminated  by  the  kidneys.  It  must 
be  inverted  before  it  can  be  changed  into  glycogen  ;  this  inversion 
takes  place  when  lactose  is  ingested  with  the  food,  but  when 
absorbed  by  the  blood  from  the  mammary  gland,  it  does  not  occur. 
Under  these  circumstances  lactose  enters  the  blood  directly  as 
lactose  and  is  excreted  in  the  urine. 

Lactosuria  is  a  condition  which  has  escaped  general  recognition, 
and  in  speaking  of  it  Hopkins  says :  "  If  the  urine  exhibits  the 
following  characters,  the  presence  of  lactose  is  established  almost 
without  the  possibility  of  doubt:  It  should  reduce  copper  and 
bismuth  solution ;  but  with  the  fermentation-test,  it  should  give 
negative  results  for  the  first  twenty-four  hours  of  the  experiment, 
and  it  should  give  no  definite  crystalline  precipitate  with  the 
phenylhydrazin  test  when  this  is  directly  applied.  On  the  other 
hand,  after  boiling  with  5  per  cent,  sulphuric  acid  for  a  short  time 
the  urine  should,  if  first  neutralized-  with  ammonia,  give  the 
phenylhydrazin  test  readily  :  crystals  of  dextrosazon  should  be  thus 
obtained,  and  with  proper  precautions  galactosazon  crystals  may 
also  be  distinguished.  Although  the  lactose  is.  converted  by  the 
mineral  acid  into  dextrose  and  galactose,  fermentation  is  not 
always  to  be  obtained  after  treatment,  as  the  large  amount  of 
sulphate  which  is  present  after  neutralizing  the  acid  interferes 
with  the  growth  of  the  yeast.  If  the  reducing  power  of  the 
urine  is  estimated,  this  should  be  found  increased  after  boiling 
with  mineral  acid,  but  unaffected  by  boiling  with  citric  acid." 


440  THE   URINE. 

Inorganic  Constituents. — The  inorganic  ingredients  which 
occur  in  the  urine  are  mainly  in  the  form  of  chlorids,  phosphates, 
sulphates,  and  carbonates,  combined  with  sodium,  potassium, 
ammonium,  calcium,  and  magnesium,  and  are  excreted  to  the 
amount  of  about  25  grams  per  diem,  of  which  about  15  grams  are 
sodium  chlorid,  derived  almost  exclusively  from  that  taken  in 
with  the  food. 

The  inorganic  constituents  eliminated  in  the  urine  come  from 
(1)  the  inorganic  constituents  of  the  food,  and  (2)  from  the  de- 
structive metabolism  of  the  body -tissues.  In  the  first  group  are 
the  chlorids  and  the  principal  part  of  the  phosphates;  in  the 
second,  the  sulphates,  which  occur  in  but  small  quantities  in  the 
food,  and  a  small  part  of  the  phosphates. 

Chlorids. — Although  the  urine  contains  some  potassium  chlorid, 
it  is  mainly  by  sodium  chlorid  that  these  salts  are  represented. 
Inasmuch  as  its  quantity  in  the  urine  depends  upon  that  taken 
in  with  the  food,  this  is  subject  to  considerable  variation.  In 
disease  any  process  which  results  in  taking  sodium  chlorid  from  the 
blood  will  correspondingly  diminish  its  excretion  in  the  urine  ; 
this  occurs  in  the  exudations  which  accompany  pneumonia  and 
pleurisy.  When  these  are  absorbed,  the  chlorid  of  sodium  again 
enters  the  blood  and  the  quantity  in  the  urine  is  increased. 

Phosphates. — In  the  metabolism  of  the  tissues  of  the  body 
some  of  the  phosphorus  contained  in  nuclein,  lecithin,  and  prota- 
gon  is  oxidized,  producing  phosphoric  acid,  which  in  the  form  of 
phosphates  is  excreted  in  the  urine ;  the  amount  of  this  is,  how- 
ever, small.  Most  of  these  salts  which  occur  in  the  urine  are 
derived  from  the  food ;  hence  their  quantity  is  increased  with  an 
animal  diet,  while  with  a  vegetable  diet  it  is  diminished.  The 
phosphates  of  plants  are  not  absorbed  by  the  animal,  because  of 
their  insolubility,  hence  in  the  urine  of  herbivorous  animals  these 
salts  are  deficient.  The  amount  of  phosphoric  acid  daily  excreted 
in  human  urine  is  about  3.5  grams. 

The  phosphates  exist  in  two  forms :  (1)  Alkaline  and  (2) 
earthy.  The  alkaline  phosphates  are  those  of  sodium  and  potas- 
sium ;  while  the  earthy  phosphates  are  those  of  calcium  and  mag- 
nesium. 

Sodium  dihydrogen  phosphate,  also  called  acid  sodium  phos- 
phate, NaH2PO4,  is  the  principal  factor  in  giving  urine  its  acid 
reaction,  although  associated  with  it  in  this  office  is  calcium 
dihydrogen  phosphate,  Ca(H2PO4)2.  When  the  reaction  of  the 
urine  is  neutral  there  are  also  present  di sodium  hydrogen  phos- 
phate, Na2HPO4,  calcium  hydrogen  phosphate,  CaHPO4,  and  mag- 
nesium hydrogen  phosphate,  MgHPO4.  When  the  urine  is  alka- 
line these  may  also  be  present,  accompanied  by  the  normal  phos- 
phates, Na3PO4,  Ca3(PO4)2,  Mg3(PO4)2,  or  these  latter  may  replace 
the  former. 


INORGANIC  CONSTITUENTS.  441 

When  the  urine  becomes  alkaline,  whether  as  a  result  of 
the  decomposition  of  urea  and  the  formation  of  ammonium  car- 
bonate or  by  the  addition  of  ammonia,  the  earthy  phosphates  are 
precipitated.  From  alkaline  decomposing  urine,  crystals  of 
ammonio-magnesium  phosphate,  magnesium  ammonium  phosphate, 
or  triple  phosphates,  by  all  of  which  names  they  are  known,  are 
deposited.  The  chemical  formula  of  this  deposit  is  NH4MgPO4 
-f  6H2O.  It  forms  coffin-lid  crystals  or  star-shaped  figures. 

Urine  that  is  slightly  acid  deposits  star-shaped  masses  of 
prisms  of  calcium  phosphate,  called  from  the  form  of  the  crystals 
stellar  phosphates. 

Sulphates. — Only  a  small  quantity  of  the  sulphates  comes  from 
the  food,  most  of  it  being  the  result  of  the  metabolism  of  the 
proteids  of  the  body,  into  which  sulphur  enters  as  a  component 
part.  These  salts  occur  in  the  urine  in  two  forms  :  (1)  Inorganic 
sulphates  and  (2)  ethereal  or  conjugated  suJphates.  The  total  amount 
of  sulphates  daily  excreted  in  the  urine  varies  from  1.5  grams  to 
3  grams,  of  which  about  one-tenth  is  in  the  form  of  the  conjugated 
sulphates.  The  conjugated  sulphates  consist  of  radicles  derived 
from  the  aromatic  substances  present  in  the  urine,  joined  with 
sulphuric  acid,  from  which  fact  they  derive  their  name.  Among 
the  most  important  of  the  ethereal  sulphates  are  phenol-potassium 
sulphate  and  indoxyl-potassium  sulphate  :  besides  these  are  kresol- 
potassium  sulphate,  skatoxyl -potassium  sulphate,  etc.  These 
salts  are  increased  when  the  putrefaction  of  proteid  substances  in 
the  intestines  is  increased.  Whenever,  therefore,  the  amount  of 
sulphuric  acid  in  the  urine  is  increased,  it  may  be  due  to  an  in- 
creased amount  of  sulphates  in  the  food  or  drink,  or  to  increased 
putrefaction  in  the  intestines. 

There  is,  according  to  Hopkins,  also  some  sulphur  in  the  urine 
in  the  form  of  neutral  sulphur,  as  contradistinguished  from  the 
"  acid  sulphur "  of  the  sulphates.  It  is  in  a  less  oxidized  form 
than  the  sulphates,  but  what  the  compounds  are  is  not  known.  It 
is  said  that  one-fifth  of  the  total  sulphur  of  the  urine  is  in  this 
form.  Some  of  this  may  come  from  the  taurin  of  the  bile. 

Carbonates. — When  the  urine  is  alkaline,  sodium,  calcium,  mag- 
nesium, and  ammonium  carbonates  are  present.  These  are  espe- 
cially abundant  after  a  vegetable  diet,  for  the  reason  that  the 
malates,  tartrates,  and  citrates  contained  in  such  food  are  con- 
verted into  carbonates,  which  are  eliminated  by  the  kidneys. 
Carbonic  acid  also  exists  in  acid  urines,  as  much  as  50  c.c.  per 
liter  having  been  found  present. 


442  MUSCLE  PHENOMENA. 

IRRITABILITY;  CONTRACTILITY;  ELECTRIC  PHENOMENA 
OF  MUSCLE. 

Irritability  is  the  property  possessed  by  living  tissues  by  virtue 
of  which  they  respond  to  certain  external  agents  called  irritants 
or  stimuli.  A  stimulus,  therefore,  is  an  agent  which  is  capable  of 
producing  in  living  tissues  certain  changes  by  which  is  manifested 
the  fact  that  they  are  living,  the  character  of  these  changes  varying 
according  to  the  tissue  which  is  the  subject  of  the  stimulation. 
When  this  change  consists  in  one  of  form,  it  is  contractility. 
Thus,  simple  protoplasm,  as  in  the  ameba,  will,  when  touched, 
draw  in  the  processes  or  pseudopodia  which  it  had  previously  put 
out  (p.  24).  Here  the  touch  was  the  stimulus  which  caused  the 
irritability  of  the  protoplasm  to  manifest  itself  by  contraction. 
Or  if  a  muscle  is  stimulated  by  an  electric  current,  it  shortens, 
thus  manifesting  its  irritability  by  contraction.  In  both  these 
instances  the  response  to  the  stimulus  is  a  change  of  form.  If, 
however,  a  current  of  electricity  is  passed  through  a  nerve,  the 
closest  inspection  fails  to  reveal  any  change  in  the  nerve  itself: 
it  neither  moves  its  position  nor  in  any  wise  changes  its  form  ; 
and  yet  a  nerve  is  irritable — i.  e.,  has  the  property  of  responding 
to  a  stimulus.  If  it  is  a  motor  nerve — that  is,  one  distributed  to 
a  muscle — when  it  is  stimulated  its  contractility  will  be  mani- 
fested by  a  contraction  of  that  muscle ;  or  if  it  is  a  secretory 
nerve — that  is,  one  supplying  a  'gland — its  irritability  will  be 
manifested  by  an  increased  activity  of  the  gland. 

It  is  riot,  however,  essential  that  in  order  to  manifest  contrac- 
tility muscles  should  be  stimulated  through  the  motor  nerve  which 
is  distributed  to  them,  as  a  stimulus  applied  directly  to  the  muscle 
itself  will  cause  the  muscle  to  contract.  That  muscular  tissue  pos- 
sesses irritability  independently  of  the  nerves  distributed  to  it  was 
for  a  long  time  in  dispute,  but  is  now  conceded  by  all  authorities, 
the  proof  which  was  furnished  by  Claude  Bernard's  experiment 
being  incontrovertible.  This  consists  in  destroying  the  brain  of  a 
frog  by  pithing  it — i.  e.,  passing  a  blunt  needle  into  the  cranial 
cavity  and  moving  it  about.  This  destroys  consciousness ;  but 
the  circulation  of  blood  continues.  The  left  sciatic  nerve  is  then 
dissected  out,  and  a  ligature  passed  beneath  it,  and  all  the  tissues 
of  the  thigh  excepting  the  nerve  are  tightly  tied  :  thus  is  cut  off 
the  blood-supply  to  all  the  parts  below  the  ligature  ;  but  the  nerve 
is  at  the  same  time  uninjured.  Under  the  skin  of  the  back  a  few 
drops  of  a  2  per  cent,  solution  of  curare  are  then  injected.  If  after 
some  time,  about  half  an  hour,  the  nerve  is  stimulated,  there  will 
be  no  contraction  of  the  muscles  supplied  by  it ;  but  if  the  stimulus 
is  applied  directly  to  the  muscles,  they  will  respond.  Experiment 
shows  that  curare  poisons  the  motor  end-plates,  so  that  although 
the  nerve  carries  the  current  to  this  end-organ,  its  influence  can 


IRRITABILITY. 


443 


pass  no  farther.  It  has  also  been  demonstrated  that  muscular 
tissue  in  which  there  are  no  nerves  will  respond  to  stimuli ;  so 
that  of  the  existence  of  independent  muscular  irritability  there  is 
no  doubt. 

Stimuli.— Stimuli  may  be  general  or  special. 

General  Stimuli. — These  are  electrical,  chemical,  mechanical, 
and  thermic.  A  current  of  electricity  will  stimulate  a  muscle  or  a 
nerve ;  certain  chemicals  will  also  stimulate  them  ;  but  there  are 
some  of  these  agents  which  will  stimulate  a  nerve  and  not  a 
muscle ;  still  others  will  stimulate  a  muscle  and  produce  no  effect 
upon  a  nerve.  A  blow  will  stimulate  either  a  muscle  or  a  nerve, 
and  is  an  instance  of  a  mechanic  stimulus,  and  heat  or  cold 
suddenly  applied  will  cause  a  response  in  either. 

Special  stimuli  are  those  whose  influence  is  restricted  to  a  single 
nervous  apparatus ;  thus  light  affects  only  the  retina ;  sound- 
waves, only  the  organ  of  Corti  ;  and  the  senses  of  smell  and  taste 
require  special  stimuli  to  excite  them. 

The  manner  in  which  stimuli  act  is  not  thoroughly  understood. 
It  is  compared  by  Sir  William  Gowers  to  the  blow  that  explodes 
dynamite  or  the  match  which  ignites  a  mass  of  gunpowder. 

Although  any  of  the  stimuli  above  mentioned  may  be  used  to 
demonstrate  irritability  and  to  study  it,  still  it  has  been  found  that 
the  most  reliable  and  satisfactory  results  are  obtained  when  an 


FIG.  245. — Experiment  for  determining 
the  irritability  of  nerves. 


FIG.  246.— Daniell  cell. 


electric  stimulus  is  used,  as  this  is  more  readily  controlled  and 
measured  than  any  of  the  other  varieties  of  stimuli,  and  for  this 
purpose  a  muscle-nerve  preparation  is  made  (Fig.  245).  It  consists 
of  the  gastrocnemius  muscle  of  a  frog  with  the  sciatic  nerve 
attached,  a  portion  of  the  bone  being  also  removed  by  which  it 
may  be  clamped  in  an  appropriate  holder.  The  electric  current 
may  be  applied  to  the  muscle  directly,  constituting  direct  stimula- 
tion, or  to  the  nerve  through  which  it  passes  to  the  muscle,  indirect 


444 


MUSCLE  PHENOMENA. 


stimulation;  the  result  in  either  case  being  a  shortening  or  con- 
traction of  the  muscle,  which  may  be  made  manifest  by  some 
device  attached  to  the  tendon  of  the  muscle. 

Battery. — For  the  generation  of  the  current  the  Daniell  cell 
(Fig.  246)  is  the  one  best  adapted  and  most  commonly  employed. 
In  it  polarization  is  prevented  and  its  constancy  is  very  great. 
Polarization  consists  in  a  diminution  in  the  intensity  of  the  cur- 
rent, caused  by  a  film  of  hydrogen  which  forms  on  the  copper  plate. 
The  Daniell  cell  consists  of  a  glass  jar  holding  dilute  sulphuric  acid 
or  a  solution  of  copper  sulphate,  in  which  is  a  sheet  of  copper  of  a 
cylindric  form.  Within  the  latter  is  a  porous  jar  containing  a  solu- 
tion of  zinc  sulphate,  within  which  is  a  zinc  prism.  To  keep  the 
solution  of  copper  sulphate  saturated,  crystals  of  this  salt  are  placed 
in  a  perforated  pocket  attached  to  the  copper  plate.  The  action  of 
the  sulphuric  acid  upon  the  zinc  results  in  chemical  changes  by  which 
a  current  of  electricity  is  generated  when  the  zinc  and  copper  are 
metallically  connected.  The  current  within  the  cell  flows  from  the 
zinc  to  the  copper,  while  outside  it  flows  from  the  copper  to  the  zinc. 
The  zinc  is  the  positive  plate,  and  the  copper  the  negative :  but  the 
end  of  the  wire  which  is  connected  with  the  copper  is  the  positive 
pole  or  anode,  and  that  connected  with  the  zinc  plate  is  the 
negative  pole  or  kathode.  When  the  unattached  ends  of  these  wires 
connecting  the  zinc  and  the  copper  are  brought  into  contact  with 
a  nerve  a  current  of  electricity  flows  through  the  nerve,  the  direc- 
tion being  from  the  anode  to  the  kathode.  The  wires  are  also 
termed  electrodes,  though  this  term  is  more  commonly  applied  to 
the  terminations  of  the  wires  attached  to  suitable  holders.  When 

the  electrodes  are  brought 
into  communication  through 
the  intervening  nerve  the 
circuit  is  closed,  and  a  con- 
traction of  the  muscle  oc- 
curs ;  when  one  of  them,  or 
both,  is  removed  from  the 
nerve  the  circuit  is  broken, 
and  another  contraction  fol- 
lows ;  or  the  same  results 
will  follow  if  the  muscle  is 
directly  stimulated  without 
the  intervention  of  the  nerve. 
Keys. — A  more  conven- 
ient method  of  stimulating 
a  nerve  or  muscle  is  by 
placing  the  one  or  the  other 
upon  the  electrodes,  which 


FIG.  247.— Electric  key. 


are  not  connected  directly,  but  through  the  intermediary  of  a  key. 
When  the  key  is  open  the  circuit  is  broken,  and  when  it  is  closed 


IRRITABILITY. 


445 


the  circuit  is  also  closed  and  a  current  passes.  The  closing  of  the 
key  is  make;  its  opening,  break;  these  being  abbreviated  expres- 
sions to  imply  that  the  circuit  is  closed  or  made,  and  open  or 
broken. 

Du  Bois-Reymond  Key  (Fig.  247). — By  this  key  the  circuit 


FIG.  248.— Electric  circuiting. 

may  be  either  closed  or  the  current  short-circuited.  In  Fig.  248 
these  two  methods  of  the  use  of  the  key  are  shown.  At  a  the 
current  is  passing  through  the  nerve  because  the  key  is  closed, 
and  at  6  it  is  not  so  passing,  because  the  key  is  open.  When  used 


FIG.  249. — Schema  of  induction  apparatus. 

in  the  manner  shown  at  c  and  d  the  battery  is  at  all  times  connected 
with  the  electrodes  which  are  in  connection  with  the  nerve,  so  that 
the  current  is  at  all  times  taking  this  path  when  the  key  is  open  at 
d  ;  but  when  the  key  is  closed,  as  at  c,  the  key  offering  less  resist- 


UOOTABILITY* 


•u: 


duood  in  tho  secondary  coil,  \vhioh  is  manifested  by  a  contraction 
of  the  muscle.  Tho  effect  upon  tho  muscle  is  brief,  and  it  returns 
to  its  former  condition,  and  so  long  as  the  onrront  is  flowing  no 
further  change  takes  place  in  it ;  but  the  moment  the  primary 
current  is  broken  the  muscle  again  contracts,  because  of  the  pro- 
duction of  another  induced  current.  It  will  be  recalled  that  with 
the  direct  lottery  current  the  closing  of  the  circuit,  or  the  ttu?&, 
produced  tho  greater  effect  upon  the  muscle;  in  the  induced 
current  it  is  the  break  which  produces  the  more  powerful  shock. 

Iht  tfoiV/frywowfs  Indudorium  (Fig.  250),— This  induction 
apparatus  is  the  one  most  commonly  used  in  physiologic  labora- 
tories. 

To  render  the  make  ami  break  shocks  of  the  secondary  coil 


I 


*.  353,  m— Pohrs  mercury  commutator. 

more  equal,  Helmholtx  connected  one  |x>lo  of  the  Ivitterv  with  r 
(Fig.  2oi>),  and  the  other  with  A,  and  A  and  r  with  a  short  and 
thick  wire.  On  account  of  the  wire  between  r  and  .1.  the  primary 
current  is  never  opened,  but  passes  through  the  primary  coil,  anil 
when  the  vibrating  spring  and  r  come  into  contact,  the  current  is 
short  -circuited. 

^fatHMtorimftfc  Ettctmlcs. — When  a  muscle  or  other  tissue 
is  placed  upon  metal  electrodes  through  which  a  current  is  passing, 
the  electrodes  hoeome  polamed  as  a  result  of  the  decomposition 
taking  place  in  the  tissue,  and  consequent!?  currents  are  set  up 
which  materially  interfere  with  a  proper  interpretation  of  the 
effects  of  the  current  from  the  battery  or  from  the  induced  cur- 
rent, as  the  ease  may  bo.  To  avoid  this,  special  forms  of  electrodes 
have  boon  devised  which  are  known  as  HnpoliirizaMt  or  MOH- 
polarisabl*  dectrod(&  Fig.  -M  shows  such  electrodes.  Kaeh  one 


448 


MUSCLE  PHENOMENA. 


consists  of  a  glass  tube,  at  one  end  of  which  is  an  opening ; 
the  lower  part  of  this  tube  is  filled  with  China  clay,  mixed  with 
normal  saline  solution,  which  projects  a  little  through  the  open- 
ing so  that  it  may  come  into  contact  with  the  tissue  to  be  in- 
vestigated. The  portion  of  the  tube  above  the  clay  is  filled  with 
a  saturated  solution  of  zinc  sulphate,  into  which  dips  an  amalga- 
mated zinc  wire.  When  the  experiment  is  of  long  duration  the 
form  represented  by  the  middle  figure  in  the  illustration  is  best 
adapted;  the  U-shaped  tube  is  filled  with  the  zinc  sulphate  solu- 


FIG.  254.— Method  of  recording  muscular  contraction  (Lombard). 

tion,  and  into  one  end  dips  the  wire,  and  into  the  other  a  glass 
tube  filled  with  clay,  on  which  the  tissue  rests. 

PohVs  Commutator  (Fig.  252). — In  order  to  reverse  the  direction 
of  the  current,  PohPs  mercury  commutator  is  used.  This  consists 
of  a  block  of  some  insulating  material,  as  paraffin  or  wood,  with 
six  cups  containing  mercury,  each  of  which  is  connected  to  a 
binding-post  In  Fig.  253,  A,  it  will  be  seen  that  a  and  b  are  con- 
nected with  the  battery,  c  and  d  with  the  electrodes,  and  e  and  / 
with  movable  wires  in  such  manner  that  c  connects  with  /  and 
d  with  e.  Above  the  block  is  a  bridge  of  some  insulating  mate- 
rial, glass  or  vulcanite,  to  which  two  semicircles  of  wire  are 
attached,  one  of  which  is  connected  with  a  wire  dipping  into  the 
cup  a,  and  the  other  with  a  wire  dipping  into  the  cup  b.  This 
bridge  can  be  rocked  back  and  forth,  so  that  if  the  ends  dip  into 
the  cups  c  and  d,  a  will  be  connected  with  c,  and  b  with  d  ;  while 


IRRITABILITY. 


449 


if  they  dip  into  e  and  /,  a  will  be  connected  with  e,  and  through 
the  cross-wire  with  d,  and  b  will  be  connected  with/,  and  through 
the  cross-wire  with  c.  This  arrangement  permits  the  battery- 
current  to  pass  by  way  of  a  and  e  down  the  nerve,  and  back  to 
the  battery  by  way  of  d  and  b  ;  or  from  the  battery  through  a,  e, 
and  d,  and  up  the  nerve  and  back  to  the  battery  by  way  of  c,  /, 
and  b. 

In  Fig.  253,  jB,  the  cross-wires  have  been  removed,  and,  as 
shown  by  the  diagram,  the  current  can  be  sent  through  c  and  d 
to  one  part  of  the  nerve,  or  through  e  and  /  to  another,  by  rocking 
the  bridge  back  and  forth. 

Myographs. — --In  order  properly  to   study  the  effects  of  the 


FIG.  255.— Spring  myograph  :  A,  B,  iron  uprights,  between  which  are  stretched 
the  guide-wires  on  which  the  travelling  plate  a  runs ;  fc,  pieces  of  cork  on  the  guides 
to  check  gradually  the  plate  at  the  end  of  its  excursion  and  prevent  jarring ;  6, 
spring,  the  release  of  which  shoots  the  plate  along ;  h,  trigger-key,  which  is  opened 
by  the  pin  d  on  the  frame  of  the  plate  (Stewart). 

induction  shocks  upon  the  nerves  and  muscles  it  is  necessary  to 
have  some  method  of  recording  the  movements  of  the  muscles  which 
these  shocks  produce.  Such  an  instrument  is  the  myograph.  The 
nerve-muscle  preparation  has  already  been  described.  The  tendon 
of  the  muscle  is  attached  to  a  lever,  and  to  this  latter  is  attached  a 
writing-point,  which  rests  against  a  piece  of  paper  wrapped  around 
a  revolving  drum,  the  paper  revolving  with  the  drum.  When  the 
muscle  contracts,  it  raises  the  lever  and  an  upward  line  is  made  by 
the  point  on  the  paper ;  when  the  muscle  relaxes,  the  lever  falls 
and  the  point  makes  a  descending  line.  Inasmuch  as  this  drum 
is  revolving  all  the  time,  these  lines  take  the  form  of  curves. 
Such  a  record  is  a  myogram  or  muscle-curve,  and  may  be  preserved 

29 


450 


MUSCLE  PHENOMENA. 


for  the  purpose  of  study.     Fig.  254  represents  the  method  of 
recording  muscular  contraction. 

Other  forms  of  the  myograph  are  the  spring  myograph  (Fig. 
255)  and  the  pendulum  myograph  (Fig.  256). 


FIG.  256.— Pendulum  myograph ;  at  the  left,  as  seen  from  the  front :  A,  bearings 
on  which  the  pendulum  swings ;  P,  pendulum ;  G,  G',  glass  plates  carried  in  the 
frames  T,  T ;  a,  pin  which  opens  the  trigger-key.  The  key,  when  closed,  is  in  con- 
tact with  c,  and  so  completes  the  circuit  of  the  primary  coil  (Stewart). 

Time-markers  or  Chronographs. — In  order  to  know  and  record 
the  length  of  time  consumed  by  various  phenomena  which  are  the 
subject  of  investigation,  various  forms  of  time-markers  are  used 
which  make  a  record  on  the  drum  at  the  same  time  that  the  myo- 


IRRITABILITY. 


451 


gram  is  being  made.  Such  an  one  is  the  electric  signal  of  Deprez 
(Fig.  258),  which  is  an  electromagnet  whose  circuit  is  closed  and 
opened  by  the  second  pendulum  of  a  clock  or  a  metronome. 
Or  for  this  purpose  a  tuning-fork  may  be  used  which  vibrates 


FIG.  257. — Time-marker;  arrangement  for  marking  two  intervals:  D,  seconds 
pendulum,  with  platinum  point,  E,  soldered  on  ;  A,  mercury  trough,  into  which  E 
dips  at  the  end  of  its  swing ;  B,  Daniell  cell ;  C,  electromagnets,  which  draw  down 
writing-lever  F  when  the  current  is  closed  by  E  dipping  into  A  ;  G,  spring  (or  piece 
of  India  rubber),  which  raises  .Fas  soon  as  current  is  broken  (Stewart). 


FIG.  258. — Electromagnetic  time-marker  connected  with  metronome.  The  pen- 
dulum of  the  metronome  carries  a  wire  which  closes  the  circuit  when  it  dips  into 
either  of  the  mercury  cups,  Hg  (Stewart). 

one  hundred  times  in  a  second,  the  writing-point  being  attached 
to  one  of  its  prongs. 

Moist  Chamber. — In  order  to  preserve  the  preparation  in  as 
normal  condition  as  possible  during  an  experiment,  it  is  enclosed 
in  a  chamber  the  air  of  which  is  kept  moist. 

Simple  Muscular  Contraction. — When  the  muscle-nerve  prep- 
aration is  stimulated  by  a  single  induction  shock,  a  single  con- 
traction of  the  muscle  results ;  this  is  a  twitch  or  a  simple  muscular 


452  MUSCLE  PHENOMENA. 

contraction,  and  its  myogram  is  shown  in   Fig.  259.     This  is  a 
simple  muscle-curve. 

Latent  Period. — The  moment  that  the   stimulus  reaches   the 
muscle  is  represented   by  a  in  the  illustration,  but  the  upward 


FIG.  259. — Myogram  from  gastrocnemius  muscle  of  frog;  beneath,  the  time  is  re- 
corded in  0.005  second  :  a,  moment  of  excitation  ;  ft,  beginning  of  contraction :  c, 
height  of  contraction  ;  d,  end  of  contraction  (Lombard). 

curve  begins  at  6.  So  that  between  these  events  there  is  an 
interval  of  0.006  second,  as  shown  by  the  lowest  line,  in  which 
the  curves  are  made  by  a  time-marker.  This  interval  is  the  latent 
period.  At  6  the  curve  begins  rapidly  to  rise,  then  more  slowly, 


FIG.  260. — Superposition  of  contractions:  1  is  the  curve  when  only  one  stimulus 
is  thrown  in  ;  2,  when  a  second  stimulus  acts  at  the  time  when  curve  1  has  nearly 
reached  its  maximum  height  (Stewart). 

when  it  reaches  its  highest  point,  c.  Then,  as  the  muscle  begins 
to  relax,  there  is  a  downward  curve  until  the  line  is  reached  from 
which  the  curve  started,  this  line  being  the  abscissa;  the  descend- 
ing curve  shows  that  the  relaxation  is  at  first  rapid,  then  becomes 
slower,  and  occupies  a  longer  time  than  the  contraction.  From 
a  to  b  occupies  about  0.006  second  ;  from  b  to  c,  about  0.05  second  ; 
from  c  to  d,  about  0.07  second.  Helmholtz,  in  his  experiments 


IRRITABILITY.  453 

upon  the  frog's  gastrocnemius,  found  that  the  latent  period  occupied 
yj-g-  second ;  the  rise  of  the  curve,  or  the  stage  of  contraction 
proper,  I^-  second;  and  the  fall  or  stage  of  elongation,  Y^-Q  :  or 


FIG.  261. — Development  of  incomplete  tetanus  and  contracture,  by  indirect 
stimulation.  A  gastrocnemius  muscle  of  a  frog  was  indirectly  stimulated  by 
breaking  induction-shocks,  of  medium  strength,  applied  to  the  sciatic  nerve. 
The  rate  was  about  8  per  second,  as  shown  by  comparison  of  the  seconds  traced 
at  the  bottom  of  the  figure  with  the  oscillations  caused  by  the  separate  contractions. 

-jig-  second  in  all.  A  close  inspection  of  the  myogram  will  show 
a  slight  rise  after  d  ;  this  is  due  to  the  elasticity  of  the  muscle,  and 
constitutes  the  stage  of  elastic  after-vibration  or  contraction-remain- 
der. Sometimes  more  than  one  of  these  curves  are  produced. 
Since  the  time  of  Helmholtz's  experiments  other  observers  have 
found  that  the  true  latent  period  is  much  shorter,  certainly  not 
more  than  ^Vo"  second,  and  probably  even  shorter  than  this,  for 


FIG.  262. — Effect  of  rapid  excitations  to  produce  tetanus.  Experiment  with  a 
gastrocnemius  muscle  of  a  frog,  excited  directly  with  breaking  induction-shocks 
of  medium  strength,  at  the  rate  of  33  per  second.  The  weight  was  about  15  grams. 
The  time  record  gives  fiftieths  of  a  second  (Lombard). 

it  is  highly  probable  that  changes  begin  immediately  in  the  muscle 
upon  the  receipt  of  the  stimulus,  although  these  changes  are  not 
at  once  apparent.  The  muscle-curve  differs  in  the  muscles  of 
different  animals  and  also  in  those  of  the  same  animal. 

Summation  of  Stimuli. — If  a  muscle  which  has  been  stimulated 
is  again  stimulated  before  the  effect  of  the  first  stimulation  has 


454 


MUSCLE  PHENOMENA. 


passed,  a  second  curve  will  be  produced,  which  will  be  higher 
than  the  first  (Fig.  260),  due  to  the  addition  of  the  second  stimu- 
lation to  the  first.  This  is  the  summation  of  stimulation,  summa- 
tion of  effects,  or  superposition  of  contraction. 

Tetanus. — When  a  series  of  stimuli  are  added  one  to  another 
before  the  effects  of  the  preceding  ones  have  passed,  so  that  the 
muscle  at  no  time  becomes  completely  relaxed,  the  condition  of 
tetanus  is  produced  :  incomplete  tetanus,  if  the  effect  of  each  stimu- 
lation can  be  seen  in  the  separate  curves  (Fig.  261),  and  complete 
tetanus,  where  these  have  disappeared  and  their  place  is  taken  by  a 


TOO 


800 


900 


1000 


1100 


1200 


1300 


1400 


1500 


1600 


1700 


FIG.  263.— Effect  of  fatigue  on  the  height  of  muscular  contractions.  The  figure 
is  a  reproduction  of  parts  of  a  record  of  over  1700  contractions  made  by  an  isolated 
gastrocnemius  muscle  of  a  frog.  The  contractions  were  isotonic,  the  weight  being 
about  20  grams.  The  stimuli  were  maximal  breaking  induction-shocks,  and  were 
applied  directly  to  the  muscle  at  the  rate  of  25  per  minute.  Between  the  first  group 
of  66  contractions  and  the  following  groups  a  rest  of  five  minutes  was  given  ;  after 
this  rest  the  work  was  continued  without  interruption  for  about  one  and  a  half 
hours.  The  second  group  of  contractions,  that  immediately  following  the  period  of 
rest,  •contains  the  first  20  contractions  of  the  new  series:  the  next  group  the  100th 
to  the  110th  ;  the  next  the  200th  to  the  210th,  and  so  on  (Lombard). 

continuous  line  (Fig.  262).     Voluntary  tetanus  is  the  term  applied 
to  the  normal  voluntary  contraction  of  a  muscle.     The  impulses 
sent  out  by  the  nerve-cells  are  generated  and  emitted  with  such 
frequency  as  to  produce  tetanus,  and  not  a  simple  contraction. 
The  character  of  the    simple    muscle-curve  is  modified  by : 


IRRITABILITY.  455 

1.  The  load  ;  2.  The  temperature  ;  3.  Previous  stimulation  ;  4.  The 
character  of  the  muscle  itself;  and  5.  Drugs. 

1.  Effect  of  the  Load. — The  extent  to  which  a  muscle  contracts 
is  increased  up  to  a  certain  point  with  the  increase  of  the  load ; 
but  when  this  point  is  reached  it  diminishes,  and  if  the  load  is 
sufficiently  increased,  its  power  to  lift  it  at  all  ceases. 

2.  Effect  of  Temperature. — Up  to  a  certain  point  cold  increases 
the  contraction ;   beyond  this  point  it  diminishes  it ;    moderate 
warmth  also  increases  the  height  of  the  contraction,  but  excessive 
heat   (exceeding  40°  C.)  coagulates  the  proteids  of  the  muscle, 
producing  heat-rigor. 

3.  Effect  of  Previous  Stimulation. — When  a  muscle  is  stimu- 
lated, each  curve  is  a  little  higher  than  the  preceding  one  for  a 
time,  the  curve  being  called  a  staircase;  then,  as  the  stimulation 
is  continued,  the  curve  falls,  and  finally  there  is  no  response  to 
the  stimulation — the  muscle  is  fatigued. 

Cause  of  Fatigue  of  Muscles. — This  is  explained  in  the  case  of 
the  muscle-nerve  preparation  by  the  fact  that  the  destruction  or 
katabolism  of  the  muscular  tissue  predominates  over  its  anabolism 
or  building  up,  and  after  a  time  its  contractile  power  is  lost. 


FIG.  264. — Myogram  of  muscle  poisoned  with  veratrin  and  that  of  a  normal 
muscle  :  a,  myogram  from  a  normal  gastrocnemius  muscle  of  a  frog — the  waves  at 
the  close  are  due  to  the  recoil  of  the  recording  lever ;  6,  myogram  from  a  gastroc- 
nemius muscle  poisoned  with  veratriii,  recorded  at  the  same  part  of  the  drum 
(Lombard). 

Fatigue  also  occurs  as  a  result  of  the  .accumulation  of  the  prod- 
ucts of  contraction,  sarcolactic  acid  anji  acid  potassium  phosphate, 
which  to  a  certain  extent  act  to  prevent  contraction,  and  when 
these  are  removed  by  the  circulating  blood  during  a  period  of  rest 
following  muscular  activity,  the  contractile  power  is  restored. 

In  the  fatigue  of  muscles  which  follows  their  use  as  the  result 
of  volition,  the  cause  is  chiefly  in  the  nerve-cells  in  which  the 
voluntary  impulses  are  generated. 

4.  Effect  Due  to  the  Character  of  the  Muscle. — Some  muscles 
contract  more  slowly  than  others,  even  in  the  same  individual ;  as, 


456  MUSCLE  PHENOMENA. 

for  instance,  those  of  the  leg  than  those  of  the  arm.  The  same 
difference  is  seen  in  the  corresponding  muscles  of  different  animals. 

5.  Effect  of  Drugs. — The  effect  of  drugs  upon  muscular  contrac- 
tion is  well  illustrated  by  injecting  veratrin  under  the  skin  of  a 
frog:  the  principal  characteristic  of  the  muscle-curve  produced 
being  the  extreme  prolongation  of  the  period  of  relaxation 
(Fig.  264). 

Rigor  Mortis. — It  has  already  been  stated  (p.  62)  that  the 
coagulation  of  the  muscle-plasma  is  the  cause  of  rigor  mortis  or 
cadaveric  rigidity,  in  which  the  muscle  becomes  opaque  and  stiff, 
and  loses  its  elasticity  and  extensibility ;  at  the  same  time  it 
becomes  warmer  and  acid  in  reaction.  Rigor  usually  appears  in 
from  one  hour  to  five  hours  after  death,  although  this  is  subject 
to  great  variation,  coming  on  more  rapidly  in  muscles  that  are 
feeble  than  in  those  that  are  strong  and  vigorous.  Thus  in  per- 
sons who  have  been  in  good  health,  dying  suddenly,  it  comes  on 
slowly ;  while  when  death  occurs  after  protracted  illness  it  comes 
on  quickly,  and  remains  but  a  short  time.  Animals  which  have 
been  hunted,  and  whose  muscles  are  consequently  exhausted  by 
fatigue,  are  the  subjects  of  early  rigor  mortis.  There  are,  how- 
ever, instances  in  which  rigor  has  come  on  very  early  in  those 
who  were  presumably  in  health  at  the  time,  although  it  is  pos- 
sible that  these  were  not  exceptions,  and  that  the  cause  of  the 
early  appearance  was  due  to  muscular  exhaustion  ;  as,  for  instance, 
soldiers  killed  in  battle  being  found  with  one  eye  closed  and  the 
other  open  in  the  act  of  taking  aim.  It  has  been  said  that  after 
death  from  lightning  or  in  the  heat  of  passion,  rigor  mortis  is 
entirely  absent ;  but  it  is  more  than  probable  that  in  such  cases 
it  comes  on  early  and  disappears  without  having  been  ob- 
served. 

Rigor  mortis,  as  a  rule,  is  first  observed  in  the  neck  and  lower 
jaw,  then  in  the  upper,  and  later  in  the  lower  extremities,  passing 
off  in  the  same  order.  There  are,  however,  exceptions  to  this. 
It  may  remain  for  from  one  to  six  days. 

Little  is  known  about  rigor  mortis  of  involuntary  muscle, 
although  this  condition  has  been  seen  in  the  heart,  stomach,  and 
uterus. 

Muscular  Tone. — If  a  relaxed  muscle  is  divided,  the  t\vo  ends 
separate — i.  e.,  each  portion  of  the  divided  muscle  contracts,  so  that 
even  in  a  so-called  relaxed  muscle  this  is  in  a  state  of  tonic  con- 
traction, and  this  condition  is  muscular  tone  or  muscular  tonus. 
The  advantage  which  accrues  from  this  is  that  when  the  muscles 
are  called  upon  to  perform  any  work  they  are  already  in  a  posi- 
tion to  effect  results  quickly,  which  would  not  be  the  case  if  it 
were  necessary  to  bring  them  from  a  state  of  complete  relaxa- 
tion to  one  of  effective  contraction.  It  is  as  if  one  desired  to 


IRRITABILITY. 


457 


move  a  boat  by  a  rope,  and  before  exerting  any  influence  on  the 
boat  was  compelled  to  take  up  a  considerable  amount  of  slack. 

Muscular  tone  is  a  reflex  action  depending  upon  the  reception 
by  the  cord  of  afferent  impulses,  under  which  stimulation  motor 
impulses  are  sent  out  to  the   muscles ;  and  if  the  afferent  nerve 
are  cut,  the  tone  disappears. 

Peristalsis. — The  difference  in  the  manner  of  contraction  of 
voluntary  muscle,  as  the  skeletal  muscles,  as  compared  with 
that  of  involuntary  muscle,  as  that  of  the  intestines,  is  very 
marked,  for  while  the  action  of  the  former  takes  place  rapidly 
and  throughout  the  entire  muscle,  the  action  of  the  latter  is 
slow,  and  moves  from  point  to  point  as  a  wave,  at  a  rate  of 
about  30  mm.  per  second,  the  contraction  occurring  at  one  part  of 
the  intestines  while  it  has  disappeared  at  another,  the  circular  coat 
being  especially  active  in  the  movement.  It  is  called  also  vermicular 
contraction.  When  the  movement  is  in  the  direction  opposite  to 
the  normal,  as  in  the  intestine  from  below  upward,  or  in  the  stomach 
from  the  pylorus  toward  the  cardia,  it  is  reversed  peristalsis. 

^ — ^ 


CL 

c 

4 

&         - 

b 

d 

\ 


FIG.  265. — Schema  to  show  the  direction  of  currents  to  be  obtained  from 
muscle.  The  schema  represents  a  cylindric  piece  of  muscle  with  normal 
longitudinal  surface  (o  c  and  6  d),  and  two  artificial  cross  sections  (a  6  and  c  d). 
The  position  of  the  equator  is  shown  by  line  e.  The  unbroken  lines  connect  points 
of  different  potential,  and  the  arrows  show  the  direction  which  the  currents  would 
take  were  these  points  connected  with  a  galvanometer.  The  broken  lines  connect 
points  of  equal  potential  from  which  no  current  would  be  obtained  (Lombard). 

Rhythmicality. — Involuntary  muscular  tissue  exhibits  the  prop- 
erty of  contracting  and  relaxing  with  a  certain  degree  of  regu- 
larity or  rhythm,  as  in  the  spleen,  where  there  are  a  true  systole 
and  a  diastole,  recurring  about  once  each  minute,  as  demonstrated 
by  the  oncometer  (p.  338). 

Electric  Phenomena  (Fig.  265). — A  normal  muscle  in  a  condi- 
tion of  rest  is  iso-electric — i.  e.,  it  is  "  equally  electric  throughout, 
and  hence  has  no  electric  current " ;  the  same  is  true  of  dead 
muscle.  If,  however,  the  muscle  is  cut,  the  electrical  condition 
is  changed,  and  if  the  part  that  is  cut  and  the  normal  part  are 
connected  to  a  galvanometer,  the  movement  of  the  magnet  at  once 


458 


MUSCLE  PHENOMENA. 


demonstrates  the  existence  of  an  electric  current  flowing  from  the 
normal  to  the  cut  portion.  If  the  muscle  is  caused  to  contract, 
the  needle  of  the  galvanometer  will  return  to  the  position  of  rest. 
The  first  current  was  formerly  called  the  current  of  rest,  but  is  now 
known  as  the  current  of  injury  or  demarcation  current  ;  while  the 
second  is  the  current  of  action,  or  negative  variation  current. 

Du  Bois  Reymond  explained  the  current  of  rest  by  supposing 
that  in  the  normal  muscle  at  rest  there  were  electric  currents  due 
to  the  fact  that  muscle  was  made  up  of  electromotive  molecules, 
and  that  each  of  these  molecules  is  positive  at  the  center  and 
negative  at  the  ends,  and  this  difference  of  electric  tension  be- 
comes manifest  when  the  muscle  is  cut  and  the  negative  ends  are 
exposed.  Hermann,  however,  denies  the  existence  of  currents  in 


FIG.  266. — Secondary  tetanus  (Lombard). 

normal  muscle,  and  attributes  their  generation  to  the  injury  to  the 
muscle  caused  by  its  action,  chemic  changes  being  thus  brought 
about.  Other  injury  than  cutting  will  produce  the  same  result, 
and  as  these  changes  take  place  at  the  point  between  the  normal 
and  injured  tissue  the  term  "  demarcation"  has  been  applied  to 
the  current  thus  produced. 

It  should  be  said,  however,  that  there  are  authorities  who  hold 
with  Du  Bois  Reymond  that  normal  muscle  in  a  condition  of  rest 
is  the  seat  of  electromotive  forces,  which  require  changed  condi- 
tions in  muscle  to  bring  them  forth. 

It  has  been  already  stated  that  dead  muscle  is  iso-electric ; 
dead  muscular  tissue  is,  however,  electrically  negative  to  normal 
living  muscle. 

Secondary  Contraction  (Fig.  266). — To  demonstrate  secondary 
contraction  two  nerve-muscle  preparations  are  made,  and  the 
nerve  of  one  is  placed  upon  the  muscle  of  the  other.  Such  an 
arrangement  constitutes  a  physiologic  rheoscope  or  rheoscopic  frog. 
When  the  nerve  of  the  first  preparation  is  stimulated,  not  only  its 
muscle,  but  also  that  of  the  second  preparation,  contracts.  If  the 
stimulation  is  single,  a  secondary  contraction  or  twitch  results ; 
while  if  the  stimuli  cause  tetanus  of  the  first  muscle,  there  will 
be  secondary  tetanus  of  the  second  muscle. 


IRRITABILITY.  459 

The  explanation  of  these  secondary  contractions  would  seem 
to  be  that  the  current  passes  through  the  first  preparation  into  the 
second ;  but  if  the  nerve  of  the  second  is  tied,  the  secondary  con- 
traction does  not  take  place,  so  that  this  explanation  is  not  a  true 
one.  Du  Bois  Raymond's  explanation  is  that  each  stimulus  applied 
to  the  first  nerve  causes  a  contraction  of  its  muscle  and  a  current 
of  action,  which  stimulates  the  nerve  of  the  second  preparation, 
and  a  contraction  of  its  muscle  follows. 


IV.  NERVOUS  FUNCTIONS. 


GENERAL  CONSIDERATIONS. 

THERE  is  a  most  intimate  relationship  existing  between  the 
different  organs  of  the  body — so  intimate,  indeed,  that  not  one  of 
the  whole  number  can  be  'said  to  be  entirely  independent  of  the 
others.  Many  illustrations  of  this  dependency  might  be  given,  but 
one  will  suffice. 

The  respirations  of  an  individual  at  rest  are  not  far  from  16 
per  minute,  and  the  pulsations  of  the  radial  artery  are,  under  the 
same  condition,  about  70.  If,  now,  he  exercises  violently,  the 
respirations  will  be  found  to  have  greatly  increased,  amounting 
perhaps  to  30  per  minute,  while  at  the  same  time  the  pulsations 
of  the  artery  will  have  reached  120  per  minute.  Is  this  change 
from  the  quiescent  condition  a  mere  coincidence,  or  is  there  a 
reason  for  it?  If  the  latter,  how  has  the  change  been  brought 
about? 

During  a  resting  condition  the  muscles  of  the  body  do  not 
make  great  demand  upon  the  blood,  and  with  the  heart  beating 
70  times  per  minute  the  muscles,  as  well  as  the  other  tissues,  are 
receiving  all  the  material  they  need  for  the  performance  of  their 
functions.  The  16  respirations  a  minute  are  also  sufficient  to 
supply  the  blood  with  all  the  oxygen  required  and  to  remove  from 
it  the  necessary  amount  of  carbon  dioxid.  When,  however,  the 
muscles  are  called  upon  for  the  increased  exertion  above  referred 
to,  they  must  have  a  greater  supply  of  the  necessary  materials,  to 
furnish  which  a  larger  amount  of  blood  must  be  sent  to  them. 
Then,  too,  as  a  result  of  the  extra  work,  more  muscular  tissue  is 
wasted,  and  the  waste  must  be  taken  away  rapidly  to  the  organs 
whose  duty  it  is  to  eliminate  it.  To  send  the  larger  supply  of 
blood  the  heart  must  beat  faster,  and  to  provide  the  increased 
oxygen  and  to  remove  the  additional  carbon  dioxid  the  respiratory 
movements  must  be  more  rapid.  The  muscles  of  the  body  have 
not  the  power  within  themselves  to  increase  their  activity,  but 
when  acted  upon  properly  from  without  they  have.  Neither  has 
the  heart-muscle  the  power  to  beat  more  quickly  until  influenced 
thereto  by  some  influence  outside  itself.  Equally  powerless  are 
the  agencies  which  produce  the  respiratory  movements.  These 
outside  influences,  by  which  the  muscles  contract  and  by  which 
the  heart  and  the  respiratory  apparatus  act  in  harmony,  are 

460 


NERVES.  461 

derived  from  the  nervous  system,  a  collection  of  organs  one  of 
whose  functions  is  to  cause  the  different  organs  to  act  harmo- 
niously. The  effect  of  a  want  of  harmony  under  the  circumstances 
just  supposed  would  be  most  disastrous.  If  the  nervous  force 
was  not  at  command  to  make  the  muscles  respond  when  their 
increased  action  was  desired,  there  would  be  a  condition  of  paral- 
ysis, or  if,  when  the  muscles  attempted  to  perform  this  added  task, 
the  heart  should  fail  to  respond,  the  effort  would  be  fruitless ;  and 
equally  unavailing  would  be  the  attempt  if  at  the  crucial  moment 
the  lungs  and  other  respiratory  organs  should  be  unresponsive. 
Many  other  illustrations  of  the  interdependence  of  the  organs 
might  be  given,  but  a  little  reflection  will  suggest  them  almost 
ad  infinitum. 

The  simplest  movements  that  are  made  require  for  their  per- 
formance the  conjoint  action  of  several,  often  many  muscles,  and 
were  it  not  for  the  exciting  and  controlling  power  of  the  nervous 
system,  instead  of  the  harmony  which  is  everywhere  and  at  all 
times  apparent,  there  would  result  the  utmost  confusion. 

In  what  has  been  said  thus  far  reference  has  been  had  only  to 
the  individual,  as  if  he  was  alone  on  the  face  of  the  earth  and 
interested  only  in  himself;  but  there  are  other  human  beings  with 
whom  he  is  constantly  brought  into  relation,  and  a  world  of  other 
animate  objects  as  well  as  an  infinite  amount  of  inanimate  matter. 
This  relationship  is  also  accomplished  through  the  nervous  system, 
principally  "by  means  of  the  special  senses.  It  will,  therefore,  be 
seen  that  the  nervous  functions  are  those  which  bring  the  different 
organs  of  the  body  into  harmonious  relations  with  one  another, 
and,  in  addition,  bring  the  individual,  through  the  special  senses 
— sight,  hearing,  etc. — into  relation  with  the  world  outside. him. 

The  nervous  system  is  made  up  of  collections  of  nervous 
tissue,  which  is  composed  of  two  kinds  of  matter — nerve-fibers 
and  nerve-cells,  with  neuroglia ;  these  have  been  already  de- 
scribed (p.  63). 

NERVES. 

Nerve-fibers  associated  together  form  nerves,  and  these  con- 
duct impulses  from  within  outward,  from  without  inward  or  from 
one  nerve-center  to  another.  Whether  it  is  the  function  of  a 
given  nerve  to  do  the  one  or  the  other  does  not  depend  upon  any- 
thing in  the  nerve  itself,  but  upon  its  relations  ;  and  there  is  every 
reason  to  believe  that  were  it  possible  to  separate  a  nerve  from  its 
anatomic  connections  and  attach  it  to  different  structures,  it  would 
be  just  as  capable  of  acting  in  its  new  relations  as  it  did  in  the 
old  ;  just  as  a  copper  wire  will  carry  equally  well  a  current  of 
electricity  to  ring  a  bell  or  to  supply  a  motor  or  to  turn  a  hand  on 
a  dial :  The  result  depends  not  upon  the  wire,  but  upon  the 
mechanism  with  which  it  is  in  connection. 


462  NERVES. 

.•*. 

Classification  of  Nerves. — There  are  three  kinds  of  nerves, 
classified  according  to  the  direction  in  which  they  carry  impulses : 
1.  Efferent;  2.  Afferent;  and  3.  Intercentral. 

Efferent  Nerves. — Inasmuch  as  nerves  of  this  kind  carry  im- 
pulses away  from  nerve-centers,  they  are  also  called  centrifugal 
nerves.  They  were  formerly  spoken  of  as  motor  nerves.  All 
motor  nerves  are  efferent,  for  they  carry  impulses  outward,  but  all 
efferent  nerves  are  not  motor.  A  nerve  which  carries  an  impulse 
to  a  muscle,  and  thus  brings  about  motion,  is  properly  called  a 
"  motor  nerve  "  ;  but  one  that  conducts  an  impulse  to  a  gland,  the 
results  of  which  are  the  activity  of  its  cells  and  the  production  of 
a  secretion,  is  improperly  named  a  motor  nerve,  although  it  is  un- 
questionably an  efferent  nerve.  Secretory  is  a  much  more  appro- 
priate name.  Efferent  nerves  may  be  divided  as  follows :  (1) 
motor  ;  (2)  vasomotor  ;  (3)  accelerator ;  (4)  secretory ;  (5)  trophic  ; 
and  (6)  inhibitory. 

Motor  nerves  terminate  in  muscles,  and  convey  to  them  im- 
pulses which  cause  and  regulate  their  contraction. 

Vasomotor  nerves,  although  distributed  to  the  muscular  tissue 
of  blood-vessels,  and  thus  act  as  motor  nerves,  regulate  the 
amount  of  blood  supplied  to  a  part,  and  it  seems  wise  to  separate 
them  from  the  purely  motor  nerves  and  put  them  in  a  class  by 
themselves. 

Accelerator  nerves  are  nerves  which  carry  impulses  that  increase 
the  rhythmic  action  of  an  organ,  as  the  sympathetic  nerves  to 
the  heart. 

Secretory  Nerves. — The  impulses  which  these  nerves  carry  to 
glands  bring  about  their  secretion.  The  chorda  tympani  is  a 
striking  example. 

Trophic  nerves  are  supposed  by  some  to  govern  the  nutrition  of 
the  structures  to  which  they  are  distributed,  entirely  independently 
of  the  regulation  of  the  blood-supply.  It  is  still  a  mooted  ques- 
tion whether  such  nerves  exist. 

Efferent  inhibitory  nerves  carry  impulses  which  restrain  or 
inhibit  the  action  of  the  organs  to  which  they  are  distributed. 
The  pneumogastric,  so  far  as  the  heart  is  concerned,  is  such  a 
nerve.  Without  its  restraining  influence  the  heart  would  beat 
much  faster. 

Afferent  Nerves. — The  fact  that  these  nerves  carry  impulses  to 
the  nerve-centers  has  led  to  their  being  called  also  centripetal 
nerves.  They  were  formerly  called  sensory  nerves,  but  there  is  the 
same  impropriety  in  using  these  terms  synonymously  as  in  the  case 
of  efferent  and  motor  nerves.  All  sensory  nerves  are  afferent,  but 
all  afferent  nerves  are  not  sensory.  Afferent  nerves  may  be  divided 
as  follows,  although  the  distinction  is  by  no  means  so  well  marked 
as  in  the  efferent  nerves  :  (1)  Sensory  ;  (2)  nerves  of  special  sense  ; 
(3)  thermic  nerves  ;  (4)  excitoreflex  ;  and  (5)  inhibitory. 


DETERMINATION  OF  THE  FUNCTION  OF  A  NERVE.    463 

Sensory  Nerves. — When  these  nerves  are  stimulated  an  impulse 
is  carried  to  a  nerve-center ;  if  this  center  is  the  brain,  the  sen- 
sation may  be  a  conscious  one,  and  may  or  may  not  be  painful. 

Nerves  of  Special  Sense. — The  impulses  carried  by  these  nerves 
do  not  give  rise  to  pain,  but  with  each  nerve  is  connected  a  special 
sensation  :  With  the  olfactory,  the  sense  of  smell ;  with  the  optic, 
the  sense  of  light ;  and  with  the  auditory,  the  sense  of  hearing. 

Thermic  Nerves. — It  is  believed  by  some  writers  that  there  are 
special  nerves  which  convey  the  sense  of  temperature  only ;  but 
this  is  still  an  unsettled  question. 

Exeitoreflex  Nerves. — In  these  nerves  there  is  an  impulse  car- 
ried to  a  nerve-center  without  producing  a  conscious  sensation : 
this  center  is  excited,  and  from  it  or  from  another  center  with 
.which  it  is  in  communication  there  goes  out  an  impulse  that,  if  it 
is  a  gland  to  which  it  is  distributed,  produces  secretion  :  such  a 
nerve  would  be  an  excitosecretory  nerve.  Or  if  it  is  distributed  to 
a  muscle,  it  produces  motion,  and  would  in  that  case  be  considered 
an  excitomotor  nerve. 

Afferent  Inhibitory  Nerves. — The  afferent  inhibitory  nerves  are 
also  called  centro-inhibitory,  to  distinguish  them  from  the  efferent 
inhibitory  nerves.  The  centro-inhibitory  nerves  carry  impulses  to 
nerve-centers,  which  are  so  affected  as  to  prevent  them  from  send- 
ing out  impulses.  A  familiar  instance  is  that  of  pinching  the  lip 
to  prevent  sneezing.  It  is,  however,  doubtful  whether  there  exists 
a  separate  class  of  nerves  performing  this  function,  rather  than 
ordinary  sensory  fibers  which  act  in  this  peculiar  manner  for  the 
moment. 

Intercentral  Nerves. — The  nerve-centers  are  intimately  con- 
nected with  one  another  by  nerves  which  are  neither  afferent  nor 
efferent,  and  which  are  called  intercentral.  As  has  been  said,  even 
the  simplest  movements  of  the  body  bring  into  action  several,  and 
sometimes  many  muscles ;  of  course,  this  action  is  more  obvious 
in  complex  movements.  To  accomplish  this,  various  nerve-centers 
must  be  at  work ;  and  that  they  may  act  harmoniously  and  pro- 
duce coordinated  movements  it  is  essential  that  they  should  be  in 
intimate  relationship.  Study  for  a  moment  the  intricate  mechanism 
brought  into  play  in  the  ordinary  act  of  picking  up  a  pin  from 
the  floor,  and  it  will  be  readily  understood  how  essential  it  is  that 
the  nerve-centers  responsible  for  these  movements  should  act  in 
the  most  perfect  harmony,  sending  to  each  muscle  just  the  right 
amount  of  nerve-force  and  at  exactly  the  right  moment ;  other- 
wise the  act  could  not  be  accomplished  in  the  perfect  manner 
that  it  is. 

Determination  of  the  Function  of  a  Nerve. — The  func- 
tion of  a  nerve  may  be  determined  by  (1)  dividing  it,  and  observ- 
ing what  function  has  been  lost ;  or  (2)  stimulating  it,  and  observing 
the  effect  of  the  stimulation.  Thus  when  a  motor  nerve  is  divided, 


464  NERVES. 

there  is  a  loss  of  power,  or  paralysis  of  motion,  in  the  muscle  sup- 
plied by  the  nerve.  If,  on  the  other  hand,  a  galvanic  current  is 
passed  through  the  nerve,  there  will  follow  contraction  of  the 
muscle.  Similarly  a  paralysis  of  sensation  will  follow  division  of 
a  sensory  nerve ;  and  when  such  a  nerve  is  stimulated,  sensation 
will  result.  When  a  nerve  is  thus  divided,  one  portion  will  remain 
in  communication  with  the  nerve-center,  and  is  called  the  central 
or  proximal  end ;  while  the  other,  which  remains  in  communica- 
tion with  the  periphery,  is  the  distal  or  peripheral  end.  Stimu- 
lation of  the  central  end  of  a  motor  nerve  produces  no  effect ; 
while  the  motion  referred  to  above  results  from  stimulation  of  its 
peripheral  end.  In  the  case  of  a  sensory  nerve,  it  is  the  reverse. 

Wallerian  Degeneration. — When  a  nerve  is  divided  the 
first  result  is  a  loss  of  its  function.  Afterward  the  nerve  under- 
goes Wallerian  degeneration,  which  results  in  changes  in  its 
structure  that  can  readily  be  seen.  Inasmuch  as  each  nerve-fiber 
develops  from  a  cell  which  later  nourishes  it,  if  the  connection 
between  the  two  is  severed,  the  nerve-fiber  undergoes  Wallerian 
degeneration,  and  in  the  case  of  a  nerve  which  is  made  up  of 
nerve-fibers  the  whole  nerve  undergoes  this  change.  This  degener- 
ation consists,  in  the  case  of  medullated  nerves,  in  the  death  of  the 
axis- cylinder,  the  breaking  up  of  the  medullary  sheath  into  drops 
of  myelin,  which  are  later  absorbed,  and  the  multiplication  of 
the  nuclei  of  the  primitive  sheath.  In  non-medullated  nerves 
the  only  result  is  the  death  of  the  axis-cylinder.  Degeneration 
begins  very  soon  after  the  section — within  a  day  or  two — 
and  throughout  the  entire  severed  portion  of  the  nerve  at  the 
same  time.  Thus  the  course  of  a  nerve,  or  a  collection  of 
nerves,  may  be  traced  throughout  its  entire  extent.  These  changes 
are  believed  to  be  due  to  the  severance  of  the  nerve  from  its 
trophic  center.  If  an  anterior  root  of  a  spinal  nerve  is  divided, 
the  distal  end,  being  separated  from  the  gray  matter  of  the  cord 
which  is  its  center  of  nutrition,  undergoes  degeneration,  while  the 
end  which  remains  connected  with  the  cord  retains  its  integrity. 
If  a  posterior  root  is  divided  between  the  cord  and  the  ganglion, 
the  degeneration  takes  place  between  the  cord  and  the  ganglion ; 
while  if  divided  below  the  ganglion,  the  degeneration  takes  place 
in  that  portion  separated  from  the  ganglion,  showing  that  the 
ganglion  is  the  nutritive  center  for  the  posterior  root. 

Regeneration  of  Nerves.— If  the  two  ends  of  a  divided 
nerve  are  brought  together  and  retained  there,  a  regeneration  may 
take  place,  and  the  new  structure  has  all  the  properties  of  the 
original  nerve.  It  will  be  remembered  that  in  the  degeneration 
which  follows  division  of  a  nerve  there  is  an  increase  in  the 
nuclei  of  the  sheath.  These  form  a  continuous  thread  of  pro- 
toplasm within  the  old  sheath,  and  around  this  protoplasm  a  new 
sheath  develops,  the  whole  forming  an  embryonic  nerve-fiber, 


ELECTROTONUS.  465 

which  unites  with  the  proximal  portion  of  the  old  fiber  still  in 
connection  with  its  nutritive  center,  and  hence  has  undergone  no 
degenerative  change.  Such  a  regenerated  fiber  has  both  conduc- 
tivity and  irritability,  the  former  appearing  as  early  as  the  third 
week,  but  the  latter  not  manifesting  itself  until  afterward.  At 
this  period  of  the  regeneration  there  is  neither  myelin  nor  axis- 
cylinder,  and  the  fiber  is  responsive  to  mechanical  stimuli,  but 
not  to  induction  shocks,  which  latter  property  returns  only  after 
the  axis-cylinder  is  developed.  The  medullary  substance  later 
appears  and  forms  a  tube ;  and  still  later  the  axis-cylinder  is 
formed,  having  its  origin  in  the  central  end  of  the  nerve — i.  e.y 
the  portion  which  is  still  in  communication  with  the  cell  from 
which  the  original  axis-cylinder  was  developed.  The  complete 
regeneration  of  a  nerve  may  take  months. 

So  far  as  known,  regeneration  does  not  occur  in  the  central 
nervous  system. 

NERVE-IMPULSES. 

The  function  of  nerve-fibers  is  to  conduct  impulses,  and  this 
from  centers  to  the  periphery,  from  the  periphery  to  centers, 
or  from  one  center  to  another.  Although  much  study  has  been 
given  to  the  subject,  exactly  what  a  nerve-impulse  is  has  never 
been  determined.  Except  an  electrical  change  in  the  nerve  itself, 
and  the  results  of  the  reception  of  the  impulses  at  the  termination 
of  the  nerve,  as  motion  in  a  motor  nerve,  secretion  in  a  secretory 
nerve,  etc.,  there  is  no  evidence  of  the  fact  that  impulses  have 
travelled  over  the  nerve.  Chemical,  mechanical,  or  thermic 
changes,  if  they  occur,  have  never  been  demonstrated. 

The  stimuli  which  excite  muscle  will  also  stimulate  nerves ; 
these  are  electrical,  mechanical,  chemical,  and  thermic ;  and  what 
has  been  said  of  these  applies  in  general  to  nerves.  It  should  be 
called  to  mind,  however,  that  induction-shocks  stimulate  nerves 
more  powerfully  than  a  voltaic  current  j  while  in  the  case  of 
muscle  it  is  the  voltaic  current  which  is  the  more  powerful 
stimulus. 

Velocity  of  Nerve-impulses  (Fig.  267). — In  the  motor 
nerves  of  human  beings  nervous  impulses  travel  at  the  rate  of 
33  meters  a  second,  and  in  sensory  nerves,  from  30  to  33  meters 
in  the  same  length  of  time. 

Electrotonus. — Although  contraction  of  a  muscle  takes  place 
at  the  make  and  break  of  a  constant  current  which  is  passed 
through  the  nerve  distributed  to  it,  and  although  no  apparent 
change  takes  place  in  the  nerve  at  either  of  these  moments,  or 
indeed  while  the  current  is  passing;,  still  during  the  latter  period 
important  changes  are  actually  taking  place,  though  they  are  not 
visible ;  these  are  changes  in  the  electrical  condition  of  the  nerve, 
in  its  excitability  and  also  in  its  conductivity,  and  are  collectively 

30 


466 


NEE  VE-IMP  ULSES. 


called  electrotonus.  This  has  been  concisely  denned  as  "a  change 
of  condition  in  nerves  traversed  by  an  electric  current."  It  also 
occurs  in  muscles. 


FIG.  267. — Arrangement  for  measuring  the  velocity  of  the  nerve-impulse:  A, 
travelling  plate  of  spring  myograph:  M,  muscle  lying  on  a  myograph  plate;  N, 
nerve  lying  on  two  pairs  of  electrodes,  E  and  E' ;  C,  Pohl's  commutator  without 
cross-wires;  K,  knock-over  key  of  spring  myograph  (only  the  binding  screws 
shown);  K',  simple  key  in  primary  circuit;  B,  battery;  P,  primary  coil;  8, 
secondary  coil  (Stewart). 

That  an  electrical  change  is  produced  in  a  nerve  by  passing  a 
constant  current  through  it,  the  polarizing  current,  may  be  demon- 
strated by  connecting  the  nerve  with  a  galvanometer.  The 


FIG.  268. — Electrotonic  alterations  of  irritability  caused  by  weak,  medium,  and 
strong  battery  currents :  A  and  E  indicate  the  points  of  application  of  the  elec- 
trodes to  the  nerve,  A  being  the  anode,  B  the  kathode.  The  horizontal  line  repre- 
sents the  nerve  at  normal  irritability ;  the  curved  lines  illustrate  how  the  irrita- 
bility is  altered  at  different  parts  of  the  nerve  with  currents  of  different  strengths. 
Curve  yl  shows  the  effect  of  a  weak  current,  the  part  below  the  line  indicating  de- 
creased, and  that  above  the  line  increased  irritability  ;  at  xl  the  curve  crosses  the 
line,  this  being  the  indifferent  point  at  which  the  katelectrotouic  effects  are  com- 
pensated for  by  anelectrotonic  effects;  y1  gives  the  effect  of  a  stronger  current,  and 
y3,  of  a  still  stronger  current.  As  the  strength  of  the  current  is  increased  the  effect 
becomes  greater  and  extends  farther  into  the  extrapolar  regions.  In  the  intrapolar 
region  the  indifferent  point  is  seen  to  advance  with  increasing  strengths  of  current 
from  the  anode  toward  the  kathode. 

current  near  the  kathode  is  the  katelectrotonic  current,  while  that 
near  the  anode  is  the  anelectrotonic  current.  These  currents  occur 
only  as  the  result  of  passing  a  constant  current  through  a  nerve, 


ELECTROTONUS.  467 

and  cease  when  the  current  ceases.  They  exist  in  living  medul- 
lated  nerves  only,  or  if  at  all  in  degenerated  nerves  but  to  a  slight 
degree. 

At  the  time  of  the  passage  of  the  current  there  is  an  increase 
in  the  excitability  or  irritability  of  the  nerve  in  the  kathodic 
region,  and  a  decrease  in  the  anodic  region  ;  the  increase  is  katelec- 
trotonus,  and  the  decrease,  anelectrotonus.  After  the  opening  of 
the  current  the  conditions  are  reversed,  the  excitability  being 
temporarily  increased  in  the  anodic,  and  decreased  in  the  kathodic 


FIG.  269. — Diagram  of  changes  of  excitability  and  conductivity  produced  in  a 
nerve  by  a  voltaic  current:  E,  changes  of  excitability  during  the  flow  of  the 
current,  according  to  Pfliiger.  The  ordinates  drawn  from  the  abscissa  axis  to  cut 
the  curve  represent  the  amount  of  the  change.  C  (1),  changes  of  conductivity 
during  the  flow  of  a  moderately  strong  current;  conductivity  greatly  reduced 
around  kathode;  little  affected  at  anode.  C  (2),  changes  of  conductivity  during 
flow  of  a  very  strong  current ;  conductivity  reduced  both  in  anodic  and  kathodic 
regions,  but  less  in  the  former.  C',  changes  of  conductivity  just  after  opening  a 
moderately  strong  current ;  conductivity  greatly  reduced  in  region  which  was 
formerly  anodic;  little  affected  in  region  formerly  kathodic  (Stewart). 

area.  The  indifferent  point  is  the  point  at  which  there  is  no 
change  in  the  excitability  of  the  nerve,  where  the  katelectro- 
tonic  and  anelectrotonic  effects  counteract  each  other;  this  will 
change  its  position  according  to  the  intensity  of  the  current, 
approaching  the  kathode  as  the  intensity  increases.  Fig.  268 
shows  the  changes  which  take  place  according  as  the  intensity 
of  the  current  is  increased. 

The  conductivity  of  a  nerve  is  also  affected  by  the  constant 
current,  the  changes  being  shown  in  Fig.  269. 


468 


THE  NERVOUS  SYSTEM. 


THE  NERVOUS  SYSTEM. 

The  nervous  system  is  divided  into  two  subdivisions :  the 
cerebrospinal  system  and  the  sympathetic  system. 

The  cerebrospinal  system  includes  the  brain  and  spinal  cord, 
which  together  form  the  cerebrospinal  axis,  and  the  nerves  which 
come  from  them,  namely,  the  cranial  and  spinal  nerves. 

SPINAL  CORD. 

The  spinal  cord  is  situated  in  the  vertebral  canal,  and  is 
covered  by  three  membranes — the  dura  mater,  arachnoid,  and 
pia  mater.  It  is  about  0.43  meter  in  length,  and,  in  general, 
is  of  a  cylindrical  shape  ;  it  weighs  42.5  grams.  It  extends  from 
the  medulla  oblongata  above  to  the  first  lumbar  vertebra  below, 
where  it  ends  in  the  filum  terminate,  although  in  fetal  life  it 
extends  to  the  bottom  of  the  sacral  canal. 

Enlargements  of  the  Spinal  Cord. — Two  enlargements 
along  the  course  of  the  spinal  cord  are  noteworthy.  The  cervical 


FIG.  270. — Different  views  of  a  portion  of  the  spinal  cord  from  the  cervical 
region,  with  the  roots  of  the  nerves.  In  A  the  anterior  surface  of  the  specimen  is 
shown,  the  anterior  nerve-root  of  its  right  side  being  divided;  in  B  a  view  of  the 
right  side  is  given;  in  C  the  upper  surface  is  shown  ;  in  D  the  nerve-roots  and  gang- 
lion are  shown  from  below :  1,  the  anterior  median  fissure ;  2,  posterior  median 
fissure ;  3,  anterior  lateral  depression,  over  which  the  anterior  nerve-roots  are  seen 
to  spread  ;  4,  posterior  lateral  groove,  into  which  the  posterior  roots  are  seen  to 
sink  ;  5,  anterior  roots  passing  the  ganglion  ;  5',  in  A,  the  anterior  root  divided  ;  6, 
the  posterior  roots,  the  fibers  of  which  pass  into  the  ganglion,  6  ;  7,  the  united  or 
compound  nerve;  7',  the  posterior  primary  branch,  seen  in  A  and  I)  to  be  derived 
in  part  from  the  anterior  and  in  part  from  the  posterior  root  (Allen  Thomson). 

enlargement  extends  from  the  third  cervical  to  the  first  or  the 
second  dorsal  vertebra,  and  the  lumbar  enlargement  is  at  the 
eleventh  and  twelfth  dorsal  vertebrae.  From  the  cervical  en- 
largement go  off  the  nerves  which  supply  the  upper,  and  from  the 
lumbar  those  which  supply  the  lower,  extremities. 


SPINAL   CORD. 


469 


470 


THE  NERVOUS  SYSTEM. 


C  D 

FIG.  272. — Four  cross-sections  of  the  human  spinal  cord:  A,  cervical  region;  in  the 
plane  of  the  sixth  spinal  nerve-root ;  B,  lumbar  region ;  (7,  thoracic  region  j  D,  sacral 
region;  X  7  (from  preparations  of  H.  Schmaus)  (Bohm  and  Davidoff). 


SPINAL  CORD.  471 

Fissures  (Fig.  270). — On  the  anterior  surface  of  the  spinal 
cord  is  a  groove,  the  anterior  median  fissure,  which  extends  to  the 
anterior  white  commissure.  On  the  posterior  surface  is  also  a  so- 
called  fissure,  the  posterior  median  fissure,  which  is  filled  with 
connective  tissue  and  blood-vessels,  and  extends  to  the  posterior 
gray  commissure.  It  will  thus  be  seen  that  the  anterior  and 
posterior  fissures  nearly  divide  the  cord  into  two  symmetrical 
halves,  which  are  connected  by  the  commissures. 

At  a  little  distance  from  the  anterior  median  fissure  on  each 
side  is  the  anterolateral  fissure.  Strictly  speaking,  this  is  not  a 
fissure,  being  rather  a  line  of  small  openings  at  which  emerge  the 
anterior  roots  of  the  spinal  nerves.  In  front  of  the  posterior 
median  fissure  and  on  either  side  is  the  posterolateral  fissure.  Here 
emerge  the  posterior  roots  of  the  nerves.  The  posterior  intermedi- 
ate furrow  is  between  the  posterior  median  and  posterolateral 
fissures. 

Columns. — The  anterior  and  posterior  median  fissures  divide 
the  cord  into  two  symmetrical  halves,  and  the  anterolateral  and 
posterolateral  fissures  subdivide  each  half  into  three  columns 
called  main  columns:  anterolateral,  posterolateral,  and  posterior 
median. 

.  Anterolateral  Column. — This  includes  that  portion  of  the  cord 
between  the  anterior  median  and  the  posterolateral  fissure.  It  is 
divided  by  some  anatomists  into  an  anterior,  situated  between  the 
anterior  median  fissure  and  the  anterior  nerve-roots,  and  a  lateral, 
the  portion  between  these  roots  and  the  posterolateral  fissure 
(Fig.  271). 

Posterolateral  Column. — This  is  the  portion  between  the  postero- 
lateral fissure  and  the  posterior  intermediate  furrow. 

Posterior  Median  Column. — This  is  also  called  posteromedial 
column.  It  is  situated  between  the  intermediate  furrow  and  the 
posterior  median  fissure.  The  posterolateral  and  posterior  median 
are  sometimes  described  together  as  the  posterior  column. 

Section  of  the  Spinal  Cord  (Fig."  273). — A  cross-section  of 
the  spinal  cord  shows  a  central  gray  substance  and  an  external 
white  substance.  The  gray  matter  presents  the  appearance  of  two 
crescents,  with  the  concavities  outward,  joined  together  by  a  band 
of  gray  matter,  the  gray  commissure.  The  points  of  the  crescents 
are  the  horns  or  cornua,  two  anterior  and  two  posterior.  The 
posterior  cornua  come  nearly  to  the  surface  of  the  cord  at  the 
posterolateral  fissure,  while  between  the  surface  and  the  extremi- 
ties of  the  anterior  cornua  there  is  considerable  white  matter. 
The  arrangement  of  the  white  matter  into  columns  is  readily 
discerned  in  this  section.  In  the  gray  commissure  is  a  small 
canal — the  central  canal — which  communicates  with  the  fourth 
ventricle  of  the  brain,  and  contains  cerebrospinal  fluid.  This 
is  a  colorless  alkaline  fluid  containing  sodium  chlorid  and  other 


472  THE  NERVOUS  SYSTEM. 

inorganic  salts,  and  about  0.1  per  cent,  of"  proteids,  principally 
proto-albumose,  with  some  serum-globulin,  and  rarely  peptone. 
Serum-albumin,  fibriuogen,  and  nucleoproteid  are  absent.  It  also 
contains  a  non-nitrogenous  reducing  substance  considered  by 
Claude  Bernard  to  be  sugar,  but  by  Halliburton  to  be  pyrocatechin 
derived  from  the  proteids. 

The  central  canal  is  lined  with  columnar  epithelium,  which  in 
fetal  life  is  ciliated,  but  the  cilia  are  often  absent  in  the  adult. 
The  canal  is  of  special  interest  in  connection  with  the  develop- 
ment of  the  cord.  Sections  of  the  cord  at  different  levels  show 
that  the  white  substance  is  most  abundant  in  the  upper  part,  and 


FIG.  273. — Transverse  section  of  half  the  spinal  cord,  in  the  lumbar  enlargement 
(semi-diagrammatic) :  1,  anterior  median  fissure  ;  2,  posterior  median  fissure ;  3,  cen- 
tral canal  lined  with  epithelium  ;  4,  posterior  commissure ;  5,  anterior  commissure ; 
6,  posterior  column  ;  7,  lateral  column  ;  8,  anterior  column  (the  white  substance  is 
traversed  by  radiating  trabeculse  of  pia  mater) ;  9,  fasciculus  of  posterior  nerve-root, 
entering  in  one  bundle ;  10,  fasciculi  of  anterior  roots,  entering  in  four  spreading 
bundles  of  fibers ;  b,  in  the  cervix  cornu,  decussating  fibers  from  the  nerve-roots 
and  posterior  commissure ;  c,  posterior  vesicular  columns.  About  half-way  between 
the  central  canal  and  7  is  seen  the  group  of  nerve-cells  forming  the  tractus  inter- 
mediolateralis ;  e,  e,  fibers  of  anterior  roots;  e',  fibers  of  anterior  roots  which 
decussate  in  anterior  commissure  (Allen  Thomson). 

gradually  becomes  less  abundant  as  the  examination  is  made  down 
the  cord.  The  cervical  and  lumbar  enlargements  are  due  to  the 
increased  amount  of  gray  matter  at  these  points. 

Minute  Structure  of  the  Cord. — Neuroglia  supports  both 
the  white  and  the  gray  matter  of  the  spinal  cord,  and  occurs  also 
under  the  pia  mater,  around  the  central  canal,  forming  the  sub- 
stantia  gelatinosa  centralis,  and  at  the  apex  of  the  posterior  horn, 
forming  the  substantia  cinerea  gelatinosa  of  Rolando  or  substantia 
gelatinosa  lateralis. 

The  white  substance  is  made  up  of  medullated  nerve-fibers  and 
blood-vessels,  in  addition  to  neuroglia.  The  medullated  nerve- 


SPINAL  CORD.  473 

fibers  in  sections  stained  with  carrnin  or  anilin  blue-black  appear 
as  clear  areas  with  the  stained  axis-cylinder  in  the  center,  the 
clear  space  being  the  medullary  substance. 

The  gray  matter  consists  of  nerve-fibers,  of  nerve-cells  and 
their  processes,  together  with  neuroglia  and  blood-vessels. 

Tracts  Of  the  Cord. — The  course  which  the  nerve-fibers 
take  in  the  columns  of  the  cord  has  been  determined  by  two 
methods:  the  embryologic  and  the  degenerative. 

The  embryologic  method,  or  method  of  Flechsig,  consists  in 
studying  the  cord  at  different  stages  of  its  development ;  and  as  in 
some  tracts  the  medullary  substance  forms  at  an  earlier  period 
than  in  others,  these  can  be  thus  differentiated  or  distinguished 
from  one  another. 

The  degenerative,  or  Wallerian,  method  consists  in  studying 
the  degeneration  which  occurs  in  nerve-fibers  when  separated 
from  their  nutritive  or  trophic  centers  (p.  464).  Sections  of  the 
cord  in  which  the  degeneration  has  taken  place  are  stained  with 
Marches  solution,  consisting  of  Miiller's  fluid  2  parts,  and  1  per 
cent,  osmic  acid  1  part :  the  degenerated  fibers  stain  black,  while 
the  other  portion  remains  practically  unstained.  A  tract  in  which 
this  degeneration  takes  place  belo\v  the  injury  or  point  of  section 
is  a  descending  tract,  and  the  degeneration  is  a  descending  degenera- 
tion ;  while  a  tract  in  which  the  process  occurs  above  the  lesion 
is  an  Ascending  tract,  and  the  change,  an  ascending  degeneration. 

These  methods  have  demonstrated  the  following  tracts  in  the 
cord  (Fig.  271),  into  which  the  main  columns  may  be  considered 
as  divided.  Each  tract  or  fasciculus  may  be  considered,  Gray 
says,  as  a  distinct  anatomic  system  and  endowed  with  special 
functions : 

1.  Direct  Pyramidal   Tract. — This  is  also  called  fasciculus  of 
Turck,  and  is  situated  in  the  anterolateral  column  next  to   the 
anterior  median  fissure.    It  is  continuous  with  the  non-decussating 
fibers  of  the  pyramid    of  the  medulla.     Besides   this   tract,  the 
anterolateral  column  contains : 

2.  Crossed  Pyramidal  Tract. — The  fibers  of  this  tract  are  con- 
tinuous with  those  forming  the  decussation  of  the  pyramid  of  the 
medulla. 

3.  Direct    Cerebellar    Tract. — Continuous   with   the   restiform 
body.  % 

4.  Anterolateral  Ground-bundle. — Continuous  with  the  forma- 
tio  reticularis  of  the  medulla. 

5.  Anterolateral  Descending  Cerebellar  Tract  (Lowenthal). 

6.  Anterolateral  Ascending  Cerebellar  Tract  (Gowers). 

7.  Tract  of  Lissauer. 

The  posterior  column  contains  : 

8.  Poster omedian,  also  called  posteromesial  and  column  of  Goll, 
which  is  continuous  with  the  funiculus  gracilis  of  the  medulla. 


474 


THE  NERVOUS  SYSTEM. 


9.  Poster olateralj  also  called  column  of  33urdach,  which  is  con- 
tinuous with  the  fuiiiculus  cuneatus. 

10.  Comma  tract. 

The  position  and  relation  of  these  tracts  can  be  better  under- 
stood by  reference  to  the  illustrations  than  by  any  verbal  descrip- 
tion. 

Grouping  of  the  Nerve-cells  (Fig.  274). — Some  of  the 
nerve-cells  of  the  cord  are  distributed  through  the  gray  matter, 
while  others  are  arranged  in  groups,  the  latter  being  larger,  and 
characterized  by  their  branching ;  they  are  multipolar  nerve-cells. 

Cells  of  the  Anterior  Horn. — In  the  anterior  cornu  are  three  of 
these  groups:  1.  Near  the  tip  on  the  inner  side;  2.  At  the  base 
on  the  inner  side ;  and  3.  On  the  outer  side  of  the  gray  matter. 


Posterior  horn T~ 

cell. 

Crossed  pyram- 
idal column. 
Golgi  cell  of 
posterior  horn. 
Direct   cerebel 
lar  column. 
Column  cells. 

Golgi's  com  mis- 
sural  cells. 
Gowers'  col-*.-' 

umn. 
Motor  cells. N 


Collaterals 
ending  in 
the  gray 
matter. 


•Direct  pyramidal  column. 

FIG.  274. — Schematic  diagram  of  the  spinal  cord  in  cross-section,  after  von 
Lenhossek,  showing  in  the  left  half  the  cells  of  the  gray  matter,  in  the  right  half 
the  collateral  branches  ending  in  the  gray  matter  (Bohm  and  Davidoff ). 

Each  cell  of  the  anterior  cornu  gives  off  an  axis-cylinder  process 
which  passes  out  into  the  anterior  nerve-roots. 

Cells  of  the  Posterior  Horn. — These  are  smaller  than  those  of 
the  anterior  cornu,  but  their  axis-cylinder  processes  do  not  pass 
into  the  posterior  nerve-roots. 

Clarke's  Column. — This  group  of  cells  is  most  marked  in  the 
thoracic  region,  and  is  situated  at  the  base  of  the  posterior  cornu. 
Their  axis-cylinder  processes  pass  into  the  direct  cerebellar  tract. 

Intermediolateral  Tract. — This  group  is  situated  on  the  outer 
side  of  the  gray  matter  in  what  is  called  the  lateral  horn  between 
the  anterior  and  posterior  cornua. 

Middle  Cell-group. — These  He  in  the  middle  of  the  crescent. 

Nerve-fibers  of  the  Gray  Matter.— These  are,  as  a  rule, 
smaller  than  those  in  the  white  substance.  In  the  posterior  cornu 


SPINAL  COED.  475 

they  form  Gerlach's  nerve-network,  in  which  small  and  larget 
nerve-fibers  exist  together.  These  fibers  can  be  traced  to  the 
medullated  fibers  of  the  posterior  nerve-roots,  and  also  to  the 
processes  of  the  ganglion-cells,  thus  bringing  these  cells  into  con- 
nection with  the  posterior  nerve-roots  through  the  network. 

The  fibers  of  the  anterior  horn  are  directly  continuous  with  the 
axis-cylinder  processes  of  the  ganglion-cells. 

The  following  illustration  (Fig.  275)  represents  the  relations 
between  the  nerve-cells,  the  skin,  and  a  muscle. 

Spinal  Nerves. — There  are  thirty-one  pairs  of  spinal  nerves, 
which  are  distributed  to  the  neck,  trunk,  and  extremities.  Each 


FIG.  275. — Schematic  diagram  of  a  sensorimotor  reflex  arc  according  to  the 
modern  neuron  theory ;  transverse  section  of  spinal  cord ;  mN,  motor  neuron ;  sN, 
sensory  neuron;  C1,  nerve-cell  of  the  motor  neuron;  C2,  nerve-cell  of  the  sensory 
neuron  ;  d,  dendrite;  n,  neuraxis  of  both  neurons ;  t,  telodendrons  ;  M,  muscle-fiber; 
h,  skin  with  peripheral  telodendron  of  sensory  neuron  (Bohm  and  Davidoff). 

of  these  arises  by  two  roots  ;  an  anterior  or  motor,  and  a  posterior 
or  sensory  root. 

Anterior  Roots. — These  are  traced  through  the  anterolateral 
column  to  the  cells  df  the  gray  matter  of  the  anterior  cornu. 
Around  the  cells  is  an  interlacement  of  ramified  nerve-endings, 
which  come  especially  from  the  collaterals  of  the  posterior  root- 
fibers  and  from  those  of  the  fibers  of  the  white  substance  of  the 
cord. 

Posterior  Roots. — These  are  characterized  by  the  presence  upon 
each  of  a  ganglion,  except  the  posterior  root  of  the  first  cervical 
nerve,  which  frequently  possesses  no  ganglion.  These  roots  have 
their  origin  in  the  cells  of  the  ganglion,  and  pass  into  the  postero- 
lateral  column,  some  entering  the  marginal  bundle  of  Lissauer, 


476 


THE  NERVOUS  SYSTEM. 


and  some  passing  into  the  posterior  cornu.  When  the  fibers  of 
the  posterior  root  enter  the  cord  they  bifurcate,  one  branch  passing 
upward,  the  other  downward.  From  the  main  fiber,  and  also  from 
the  branches,  pass  collaterals,  which  end  in  the  gray  matter  in 
arborization,  and  in  the  nerve-cells  of  the  anterior  and  posterior 
cornua.  In  the  same  manner  end  the  main  fiber  and  its  branches ; 
some,  however,  pass  upward  in  the  posterolateral  and  posteromesial 


FIG.  276.— Transverse  section  through  half  the  spinal  cord,  showing  the  ganglia : 
A,  anterior  cornual  cells;  B,  axis-cylinder  process  of  one  of  these  going  to  posterior 
root ;  c,  anterior  (motor)  root ;  D,  posterior  (sensory)  root ;  E,  spinal  ganglion  on 
posterior  root ;  F,  sympathetic  ganglion  ;  G,  ramus  communicans ;  H,  posterior 
branch  of  spinal  nerve ;  7,  anterior  branch  of  spinal  nerve ;  a,  long  collaterals  from 
posterior  root-fibers  reaching  to  anterior  horn  ;  6,  short  collaterals  passing  to  Clarke's 
column  ;  c,  cell  in  Clarke's  column  sending  an  axis-cylinder  (d)  process  to  the  direct 
cerebellar  tract:  e,  fiber  of  the  anterior  root;  /,  axis-cylinder  from  sympathetic 
ganglion  cell,  dividing  into  two  branches,  one  to  the  periphery7,  the  other  toward 
the  cord  ;  g,  fiber  of  the  anterior  root  terminating  by  an  arborization  in  the  sympa- 
thetic ganglion  ;  h,  sympathetic  fiber  passing  to  periphery  (Ramon  y  Cajal). 

columns,  and  end  in  the  medulla  by  arborizing  around  the  cells  of 
the  nucleus  gracilis  and  cuneatus. 

Spinal  Ganglia. — The  structure  of  these  ganglia  has  been 
already  described.  Beyond  the  ganglion  the  two  roots  unite  to 
form  the  trunk  of  the  spinal  nerve,  which  passes  out  through  the 
inter  vertebral  foramen,  and  gives  off  a  recurrent  branch  to  the 
dura  mater  of  the  cord.  It  then  divides  into  a  posterior  division, 
which  is  distributed  to  the  posterior  part  of  the  body.,  and  an  ante- 


SPINAL  CORD. 


477 


rior  division  which  goes  to  the  anterior  part ;  each  division  contains 
fibers  from  both  roots. 

Functions  of  the  Spinal  Cord. — The  functions  of  the 
spinal  cord  are  of  two  kinds :  1.  A  conductor  of  impulses,  by 
virtue  of  the  fibrous  nervous  matter  which  it  contains ;  and  2. 
A  nerve-center,  by  virtue  of  its  nerve-cells. 

As  a  Conductor  of  Impulses. — The  spinal  cord  is  the  principal 
channel  through  which  all 
impulses  from  the  trunk 
and  the  extremities  pass 
to  the  brain,  and  all  im- 
pulses to  the  trunk  and 
extremities  pass  from  the 
brain.  If  through  disease 
"or  injury  the  cord  is  disor- 
ganized at  any  point,  all 
power  to  produce  volun- 
tary motion  in  the  parts 
below  the  injury  is  lost, 
and  conscious  sensation  in 
these  parts  is  from  that 
moment  abolished.  The 
cord  therefore  acts  as  a 
conductor  of  impulses, 
both  motor  and  sensory, 
between  the  brain  and  the 
trunk  and  extremities  ;  the 
different  kinds  of  impulse 
follow  different  paths  in 
the  cord. 

Concluding-paths  in  the 
Cord. — The  paths  by  which 
voluntary  motor  impulses 
traverse  the  cord  are  fairly 
well  ascertained.  These  im- 
pulses originate  in  the  pyr- 
amidal cells  of  the  cerebral 


cortex,  and  pass  through  the 
pyramids  in  the  medulla, 
crossing  principally  at  the 


FIG.  277.— Schema  showing  pathway  of  the 
sensory  impulses.  On  the  left  side,  S,  &,  repre- 
sent afferent  spinal  nerve-fibers  ;  C,  an  afferent 
cranial  nerve-fiber.  This  fiber  in  each  case  ter- 
minates near  a  central  cell,  the  neuron  of  which 

" .  *  p1      , "  crosses  the  middle  line  and  ends  in  the  opposite 

decussation     OI     the     pyra-      hemisphere  (van  Gehuchten). 

mids,  and  to  a  less  degree 

in  the  upper  part  of  the  cord,  to  the  opposite  side,  whence  they 
follow  the  course  of  the  pyramidal  tracts,  direct  and  crossed,  arbo- 
rizing around  the  cells  of  the  anterior  cornua ;  from  which  the 
anterior  roots  arise  to  be  distributed  to  the  muscles. 

The  course  pursued  by  the  sensory  impulses  (Fig.  277)  is  not 


478  THE  NERVOUS  SYSTEM. 

so  well  understood  as  is  that  of  the  motor.  Bat  the  best  opinions 
may  be  summarized  as  follows  : 

Tactile  and  muscular  sense-impressions  pass  up  the  posterior 
columns  to  the  nucleus  gracilis  and  nucleus  cuneatus,  by  the 
internal  arcuate  fibers  and  fillet  to  the  optic  thalamus,  by  the 
posterior  part  of  the  internal  capsule  to  the  Kolandic  area  of  the 
opposite  side. 

Painful  impressions,  and  those  of  heat  and  cold,  pass  up  the 
gray  matter  of  the  cord  from  cell  to  cell  to  the  optic  thalamus, 
and  by  the  fibers  of  the  corona  radiata  to  the  cortex. 

Afferent  impulses  reach  the  cerebellum  by  Clarke's  column, 
direct  cerebellar  tract,  restiform  body,  and  inferior  peduncles. 
The  fibers  composing  the  tract  of  Gowers  have  their  origin  in 
cells  at  the  base  of  the  anterior  cornu,  on  the  opposite  side,  and 
its  cerebellar  fibers  pass  to  the  middle  lobe  by  the  superior 
peduncles. 

There  are  other  fibers  in  the  cord,  which  have  their  origin  in 
the  cerebellum  ;  but  although  their  existence  has  been  ascertained 
their  destination  is  not  certainly  determined,  though  it  is  thought 
by  some  that  they  arborize  around  cells  in  the  anterior  cornua. 

As  a  Nerve-center. — Besides  the  function  which  the  cord  per- 
forms as  a  conductor  of  motor  and  sensory  impulses,  it  also  acts 
as  a  nerve-center  in  which,  by  virtue  of  its  nerve-cells,  afferent 
impulses  are  received  and  motor  impulses  are  generated. 

Voluntary  motion  in  the  extremities,  which  motion  originates 
in  the  brain,  is  abolished  when  the  cord  is  divided  and  its  ana- 
tomic connection  with  the  brain  cut  off;  but  there  still  remains 
the  power  of  exciting  muscular  contractions  in  these  muscles,  due 
to  the  cells  of  the  cord  itself. 

Reflex  Action. — If  a  frog  is  decapitated,  it  has  no  longer  the 
power  of  producing  voluntary  movements ;  but  if  the  skin  of  a 
foot  is  irritated  by  pinching,  the  foot  is  pulled  away  from  the 
source  of  irritation.  This  is  an  instance  of  reflex  action.  A  slight 
pinch  will  cause  only  the  one  foot  to  be  withdrawn ;  but  if  it  is 
stronger,  the  other  foot  may  also  be  withdrawn.  This  is  known 
as  a  spreading  of  reflexes.  Such  movements  are  not  spontaneous, 
but  they  require  the  application  of  a  stimulus  for  their  production. 
The  irritation  does  not  act  upon  the  muscles  directly,  but  through 
the  medium  of  nerves,  an  afferent  nerve  carrying  the  sensory 
impulse  inward  to  the  cord,  and  an  efferent  nerve  conducting  a 
motor  impulse  outward  to  the  muscles.  If  either  of  these  nerves 
is  divided,  the  action  does  not  take  place ;  nor  does  it  if  the  gray 
matter  is  broken  up.  For  the  performance  of  a  reflex  act,  there- 
fore, three  things  are  necessary — an  afferent  nerve,  a  nerve-center, 
and  an  efferent  nerve,  all  in  a  physiologic  condition. 

This  can  be  readily  understood  by  reference  to  Fig.  275,  where 
h  represents  the  skin,  from  which  passes  an  afferent  nerve  to  the 


SPINAL  COED.  479 

center,  and  C1  represents  a  cell  in  the  anterior  cornu  of  the  cord, 
from  which  passes  a  motor  impulse  to  the  muscle  M. 

In  the  human  subject,  when  the  cord  is  injured  or  diseased  at 
any  point,  so  as  to  cut  off  communication  between  the  brain  and 
extremities,  but  is  still  intact  below  this  point,  tickling  of  the 
soles  of  the  feet  will  be  followed  by  their  withdrawal,  although 
the  individual  will  be  entirely  unconscious  of  any  sensation. 
This  is  also  an  instance  of  reflex  action.  As  in  the  frog,  so  in 
man,  the  three  structures  mentioned  must  exist  in  a  state  of 
integrity  for  the  performance  of  this  act. 

It  is  not  essential,  however,  that  the  cord  be  diseased  in  order 
to  have  it  manifest  reflex  action  :  this  property  is  one  which 
normally  resides  in  the  cord.  Thus  if  the  hand  comes  in  contact 
with  a  flame,  it  is  immediately  withdrawn.  This  is  not  a  voluntary 
act,  for  the  act  of  withdrawal  takes  place  before  the  sensation  of 
pain  is  felt  in  the  brain.  It  is  a  purely  reflex  act,  in  which  the 
gray  matter  of  the  cord,  after  being  stimulated  by  an  impulse 
carried  to  it  by  an  afferent  nerve,  generates  an  impulse  which  is 
conveyed  by  an  efferent  nerve  to  the  muscles  concerned  in  with- 
drawing the  arm.  The  afferent  nerve,  nerve-center,  and  efferent 
nerve  form  a  reflex  arc.  If  the  attention  was  fixed  upon  the 
subject  at  the  time  the  burn  was  received,  it  might  be  possible 
to  prevent  the  withdrawal.  This  would  be  an  instance  of  inhibi- 
tion of  reflex  action. 

Reflex  Time. — From  the  moment  when  the  stimulus  is 
applied  to  the  moment  when  the  reflex  action  takes  place  is  an 
appreciable  interval  of  time,  part  of  which  is  occupied  by  the 
passage  of  the  afferent  impulse  to  the  center,  part  by  the  passage 
of  the  efferent  nerve  to  the  muscle,  part  by  the  latent  period  of 
the  muscular  contraction,  and  part  by  the  reception  of  the  afferent 
impulse  and  the  generation  of  the  efferent  impulse  in  the  center 
itself;  this  latter  is  the  reflex  time.  In  the  frog  it  varies  from 
0.008  to  0.015  second.  Heat  and  an  increase  in  the  strength  of 
the  stimulation  lessen  it. 

Reflexes  in  Man. — The  presence  or  absence  of  certain 
reflexes  is  made  use  of  to  determine  the  presence  or  absence  of 
certain  diseases  in  the  human  subject.  They  are  included  in  two 
groups,  superficial  and  deep. 

Superficial  Reflexes. — Of  these,  there  are  many,  but  the  princi- 
pal ones  are : 

1.  Plantar. — Tickling  the  sole  of  the   foot  causes  its  with- 
drawal. 

2.  Gluteal. — Pricking  of  the  skin  over  the  gluteus  causes  a 
contraction  of  that  muscle. 

3.  Cremasteric. — Stimulating  the  skin  on  the  inner  side  of  the 
thigh  causes  a  retraction  of  the  testicle. 


480  THE  NERVOUS  SYSTEM. 

4.  Abdominal. — Stimulating  the  skin  of  the  abdomen  causes 
a  contraction  of  muscles  in  this  region :   when  this  occurs  in  the 
epigastric  region  it  constitutes  the  epigastric  reflex. 

5.  Nasal. — Stimulation  of  the  nasal  mucous  membrane  causes 
sneezing. 

6.  Conjunctival. — Touching  the  eyeball  causes  closure  of  the 
eyelids. 

Deep  Reflexes. — These  are  called  also  tendon  reflexes,  but  are 
not  true  reflexes  as  are  the  superficial  ones,  being  caused  by  direct 
stimulation  of  the  muscles  or  their  tendons. 

1.  Tendo  Achillis  Reflex. — If  while  the  extended  leg  is  sup- 
ported at  the  knee  a  hand  is  firmly  pressed  against  the  ball  of  the 
foot,  a  tap  on  the  tendo  Achillis  causes  the  gastrocnemius  and 
soleus  to  contract  and  draw  the  heel  up  quickly.     This  may  exist 
or  not  during  health. 

2.  Ankle-clonus. — The  leg  being  supported,  the  ball  of  the  foot 
is  suddenly  pressed  so  as  to  put  the  muscles  of  the  calf  on  the 
stretch,  and  there  results  a  series  of  clonic  contractions  of  these 
muscles   which   cease  when    the   pressure   is  removed.      This  is 
absent  in  health. 

3.  Patellar  Reflex  or  Knee-jerk. — If  one  thigh  is  crossed  over 
the  other,  a  tap  on  the  tendon  below  the  patella  causes  a  forward 
movement  of  the  leg.      This  is  present  in  health,  but  may  be  in- 
creased or  abolished  in  disease. 

Other  Functions  of  the  Cord  as  a  Nerve-center. — The  power  of 
the  spinal  cord  to  respond  to  afferent  impulses  independently  of 
the  will  is  of  great  advantage  in  preserving  the  body  from  injury. 
The  attempt  to  retain  one's  equilibrium  after  slipping  on  a  side- 
walk, and  the  raising  of  the  arms  in  front  of  the  face  to  ward  off 
an  unexpected  blow,  are  both  instances  of  this  action. 

Walking r,  playing  on  musical  instruments,  and  similar  acts  are 
all  performed  under  the  influence  of  the  gray  matter  of  the  cord. 
To  start  them  requires  the  action  of  the  brain,  but  when  once  they 
are  begun  their  continuance  is  accomplished  by  the  cord,  and  the 
brain  can  be  busy  about  other  things  without  interfering  in  the 
slightest  degree  with  the  perfection  of  their  performance.  Indeed, 
any  attempt  to  control  them  is  more  apt  to  hinder  than  to  help 
them.  Thus  in  coming  rapidly  down  a  flight  of  steps,  if  the 
spinal  cord  is  permitted  to  take  charge  of  the  act  the  descent  will 
be  made  with  ease  and  safety,  but  if  each  step  is  made  as  the 
result  of  volition,  the  chances  of  stumbling  or  of  tripping  are  very 
much  increased. 

The  reflex  action  of  the  cord  may  be  diminished  by  shock  to 
the  nervous  system  ;  thus  in  the  frog  immediately  after  decapita- 
tion the  reflex  power  cannot  be  excited,  but  after  a  short  time  it 
manifests  itself  under  the  influence  of  a  stimulus.  A  similar 


SPINAL  CORD.  481 

diminution  of  the  reflex  power  of  the  cord  may  be  caused  by 
opium,  by  chloroform,  and  by  some  other  substances,  while  the 
reflex  action  is  increased  by  strychnin.  If  under  the  skin  of  the 
decapitated  frog  a  solution  of  strychnin  is  injected,  the  cord  in  a 
short  time  becomes  so  irritable  that  a  stimulus  which  before  would 
have  had  no  effect  will  now  produce  the  most  marked  results,  a 
slight  blow  upon  the  skin  sufficing  to  throw  the  animal  into  a  con- 
vulsive state.  In  tetanus  the  same  irritable  condition  of  the  cord 
exists,  and  in  this  state  the  patient  may  be  thrown  into  convulsions 
by  the  simple  opening  and  closing  of  a  door. 

Special  Centers  in  the  Cord. — It  is  the  practice  to  speak 
of  certain  centers  as  existing  in  the  spinal  cord — that  is,  of 
definite  collections  of  cells  which  preside  over  definite  functions. 
Among  these  centers  the  following  have  been  described  :  Musculo- 
tonic,  respiratory,  cardio-accelerator,  vasomotor,  sudorific,  cilio- 
spinal,  genitospinal,  anospinal,  vesicospinal,  trophic,  for  erection 
of  the  penis,  for  parturition,  and  others. 

Musculotonic  Center. — This  center  is  continually  discharging 
impulses  which  keep  the  muscular  system  in  a  condition  of  slight 
contraction :  this  is  called  muscular  tone.  It  is  questionable 
whether  this  condition  is  to  be  attributed  to  any  special  center 
rather  than  to  the  action  of  all  those  cells  whose  function  it  is  to 
send  out  motor  impulses. 

Respiratory  Center. — The  respiratory  center  is  in  the  medulla, 
but  experiments  in  which  this  structure  has  been  destroyed  while 
some  respiratory  movements  persisted  demonstrate  that  to  a  cer- 
tain extent,  doubtless  very  slight,  the  spinal  cord  controls  the 
respiratory  processes. 

Cardio-accelerator  Center. — The  spinal  cord  through  the  cardiac 
nerves  and  plexus  sends  impulses  to  the  heart,  causing  it  to  beat 
more  rapidly — that  is,  they  accelerate  its  movements.  These 
impulses  are  not  constantly  emitted  as  are  the  inhibitory  impulses, 
which  travel  by  the  pneumogastric. 

Vasomotor  Center. — The  vasomotor  center  in  the  cord  is  entirely 
subsidiary  to  that  in  the  medulla. 

Sudorific  Center. — The  existence  of  special  nerves  controlling 
the  secretion  of  sweat  seems  to  be  demonstrated.  These  nerves 
come  from  the  spinal  cord,  being  a  part  of  the  anterior  roots. 

Ciliospinal  Center. — Nerve-fibers  pass  from  this  center  to  the 
iris,  and  they  are  concerned  in  the  dilatation  of  the  pupil.  These 
fibers  come  out  from  the  cord  through  the  anterior  roots  of  the 
spinal  nerves,  from  the  fifth  cervical  to  the  fifth  thoracic,  and 
join  the  cervical  sympathetic. 

Genitospinal  Center. — The  genitospinal  is  the  center  which 
governs  the  emission  of  semen,  and  is  situated  in  the  lumbar 
region  of  the  cord.  Sensory  impulses  from  the  glans  penis  reach 
this  center  through  afferent  nerves  and  stimulate  it,  and  from  it 


482  THE  NERVOUS  SYSTEM. 

go  out  efferent  impulses  which  cause  contraction  of  the  muscular 
fibers  of  the  vasa  deferentia,  seminal  vesicles,  and  accelerator 
urinae,  the  result  of  which  is  to  produce  an  ejection  of  semen. 

Anospinal  Center. — The  act  of  defecation  is  governed  by  the 
anospinal  center  and  has  been  already  described  (p.  266). 

Vesicospinal  Center.— The  act  of  micturition  is  under  the  in- 
fluence of  the  vesicospinal  center.  This  act  has  been  already 
described  (p.  430). 

Trophic  Centers. — It  has  already  been  seen  that  when  nerve- 
fibers  are  divided  they  undergo  degeneration,  and  that  this  is  ex- 
plained by  the  fact  that  under  these  circumstances  their  connection 
with  certain  nerve-cells  is  severed,  and  that  they  are  thus  deprived 
of  the  nutritive  influence  which  such  centers  exert.  Such  centers 
are  called  trophic  centers,  and  the  cells  of  the  anterior  cornua  of 
the  cord  and  the  ganglia  on  the  posterior  roots  of  the  spinal  nerves 
are  familiar  illustrations.  That  these  are  true  trophic  centers  for 
nerves  seems  to  be  beyond  dispute,  but  this  is  an  entirely  different 
question  from  that  which  deals  with  trophic  nerves  as  regulating 
the  nutrition  of  tissues  other  than  nerves.  About  the  existence 
of  such  nerves  there  is  considerable  doubt. 

Other  Centers. — Some  writers  describe  a  center  for  erection  of 
the  penis,  and  locate  it  in  the  lumbar  enlargement.  The  afferent 
nerves  from  the  penis  cause  this  center  to  send  out  efferent  im- 
pulses by  which  the  blood-vessels  are  dilated  and  the  muscles  are 
compressed,  thus  preventing  the  return  of  the  venous  blood  from 
the  penis  and  bringing  about  erection.  A  center  for  parturition 
is  described  as  being  located  in  the  lumbar  region  of  the  cord, 
above  the  centers  already  mentioned ;  under  the  influence  of  this 
the  muscular  tissue  of  the  uterus  contracts  at  the  proper  time  and 
expels  the  fetus.  Other  reflex  centers  are  described,  but  the 
tendency  to  extend  the  number  of  such  centers  seems  to  be  beyond 
what  the  actual  facts  warrant.  However,  enough  has  been  said 
to  show  the  great  importance  of  the  spinal  cord  as  a  nervous 
center,  independently  of  its  function  as  a  conductor  of  nervous 
impulses  to  and  from  the  brain. 

Functions  of  Spinal  Nerves. — Stimulation  of  an  anterior 
root  causes  contraction  in  the  muscle  to  which  it  is  distributed, 
while  its  division  is  followed  by  a  loss  of  motion  in  the  same 
muscle.  In  neither  instance  is  sensation  affected.  If  after  the 
division  the  distal  portion  of  the  nerve  is  stimulated,  muscular 
contraction  will  follow,  while  stimulation  of  the  proximal  end, 
that  which  is  in  connection  with  the  cord,  will  produce  no  effect. 
The  anterior  roots  are  therefore  efferent  and  motor,  and  are  dis- 
tributed to  muscles. 

Stimulation  of  a  posterior  root  causes  a  sensation  of  pain  in  the 
part  to  which  the  nerve  is  distributed.  Division  of  the  root 
causes  a  loss  of  sensation  in  that  part.  If  after  division  the 


THE  BRAIN.  483 

distal  portion  of  the  nerve  is  stimulated,  no  effect  is  produced, 
while  stimulation  of  the  proximal  portion  produces  sensation. 
The  posterior  roots  are  therefore  afferent  and  sensory  and  are  dis- 
tributed to  the  skin.  The  two  roots  uniting  form  a  mixed  nerve 
— that  is,  one  in  which  there  are  both  motor  and  sensory  fibers. 

Recurrent  Sensibility. — When  the  distal  end  of  a  divided  an- 
terior root  is  stimulated,  besides  the  muscular  contraction  which 
follows  there  is  also  some  pain  produced.  If  the  trunk  of  the 
nerve  beyond  the  ganglion  is  divided,  and  then  the  anterior  root 
is  stimulated,  no  muscular  contraction  results,  but  the  pain  is  felt 
as  before.  If,  however,  the  posterior  root  is  divided,  no  sensation 
is  produced.  The  sensation  experienced  when  the  anterior  root  is 
stimulated  is  accounted  for  by  the  presence  in  this  root  of  some 
sensory  fibers  which  pass  up  into  it  for  a  short  distance  and  form 
a  loop,  returning  to  the  junction  of  the  two  roots,  and  then  pur- 
suing their  course  in  the  posterior  root.  These  are  called  recurrent 
sensory  fibers.  The  impulse  passes  along  these  fibers  to  the  point 
of  junction  of  the  two  roots,  and  then  along  the  posterior  root  to 
the  nerve-center. 

Function  of  the  Spinal  Ganglia. — As  has  already  been  stated, 
upon  each  posterior  root  of  a  spinal  nerve,  with  one  exception,  is 
a  ganglion.  When  examined  under  the  microscope,  the  root-fibers 
spread  out,  passing  between  groups  of  large  cells  having  promi- 
nent nuclei  and  a  diameter  of  about  100  p.  With  one  of  these 
ganglion-cells  a  root-fiber  is  in  communication,  and  the  function 
of  these  cells  is  to  form  the^  fibers  and  to  regulate  their  nutrition ; 
they  are  true  trophic  centers. 

THE  BRAIN. 

The  6mm,  or  encephalon  (Figs.  278,  279),  is  that  part  of  the 
cerebrospinal  axis  situated  within  the  cranium  or  skull.  Its 
divisions  are  sometimes  described  as  the  forebrain,  including  the 
hemispheres,  with  the  olfactory  lobe,  the  corpora  striata,  and  the 
optic  thalami ;  the  midbrain,  being  the  corpora  quadrigemina  and 
the  crura  cerebri ;  and  the  hindbrain—tfiat  is,  the  cerebellum,  the 
pons  Varolii,  and  the  medulla  oblongata. 

In  the  adult  male  the  brain  weighs,  on  an  average,  1415  grams ; 
its  weight  in  the  female  is  about  1245  grams.  In  278  cases  of  males 
in  which  the  brain  was  weighed  the  maximum  was  1841  grams 
and  the  minimum  963  grams.  In  191  cases  of  females  the  max- 
imum Avas  1586  grams  and  the  minimum  878  grams.  The  brain 
of  Cuvier,  the  great  naturalist,  weighed  1815  grams;  that  of  an 
idiot  weighed  651  grams.  The  brain  of  a  mulatto  not  remarkable 
for  intelligence  weighed  1927  grams.  The  forebrain  weighs  about 
1245  grams  in  the  adult  male. 

The  gray  matter  of  the  brain  is  in  some  parts  on  the  surface, 


484 


THE  NERVOUS  SYSTEM. 


as  in  the  convolutions  of  the  cerebrum ;  in  other  parts  it  is 
deeply  situated,  as  in  the  basal  ganglia — i.  e.,  the  corpora  striata, 
optic  thalami,  etc.  (p.  499) ;  while  in  still  other  parts  it  is  scattered 
about  without  any  fixed  arrangement,  as  in  the  pons  Varolii.  The 
white  matter  is  made  up  of  fibers  which  come  from  the  spinal 
cord ;  of  fibers  having  their  origin  in  the  gray  matter,  and  which, 
escaping  from  the  skull,  go  to  their  points  of  distribution  as  the 


FIG.  278.— Base  of  brain :  i;  2,  3,  cerebrum  ;  4  and  5.  longitudinal  fissure ;  6, 
fissure  of  Sylvius;  7,  anterior  perforated  spaces;  8,  infundibulum  ;  9,  corpora  albi- 
cautia ;  10,  posterior  perforated  space  ;  11,  cruri  cerebri ;  12,  pons  Varolii ;  13,  junc- 
tion of  spinal  cord  and  medulla  oblongata ;  14,  anterior  pyramid ;  14X,  decussation 
of  anterior  pyramid;  15,  olivary  body;  16,  restiform  body;  17,  cerebellum;  19, 
crura  cerebelli;  21,  olfactory,  sulcus;  22,  olfactory-  tract;  23,  olfactory  bulbs;  24, 
optic  commissure;  25,  motor  oculi  nerve:  26,  patheticus  nerve;  27,'  trigeminus 
nerve  ;  28,  abducens  nerve ;  29,  facial  nerve ;  30,  auditory  nerve ;  31,  glossopharyn- 
geal  nerve;  32,  pneumogastric  nerve;  33,  spinal  accessory  nerve;  34,  hypoglossal 
nerve. 

cranial  nerves ;  and  of  still  other  fibers  connecting  the  ganglia 
with  one  another,  forming  commissures. 

The  Medulla  Oblongata.— The  medulla  oblongata,  or  bulb,  is 
the  continuation  of  the  spinal  cord,  and  is  about  2.5  cm.  long,  2  cm. 
broad,  and  1.2  cm.  thick.  It  is  composed  of  gray  and  white  matter. 
The  gray  matter,  which  in  the  cord  has  the  characteristic  double 
crescentic  shape,  approaches  more  and  more  the  posterior  surface 


THE  BRAIN. 


485 


of  the  cord  as  the  region  of  the  medulla  is  reached,  and  the  pos- 

terior cornua  become  more  and  more  external,  the  whole  mass  of 

gray  matter  flattening  out,  until  in  the  medulla  it  forms  a  layer 

the  outer  portions  of  which  represent  the  posterior  horns  and  the 

middle  portions  the  anterior.    The 

posterior  columns  separate  in  the 

medulla,  the  central  canal  coming 

to  the  surface  posteriorly  and  end- 

ing in  the  fourth  ventricle,  the  floor 

of  which  is  the  gray  matter  above 

referred  to,  which  is,  however,  not 

limited  to  this  site,  but  is  pres- 

ent  also   about  the  aqueduct  of 

Sylvius.     From  this  gray  matter 

arise  all  the  cranial  nerves  except- 

ing the  olfactory  and  optic. 

The  medulla,  like  the  cord,  has 
an  anterior  and  a  posterior  median 
fissure.  At  the  lower  part  of  the 
anterior  fissure  are  fibers  that  cross 
from  side  to  side,  the  decussation  of 
the  anterior  pyramids.  The  pos- 
terior fissure  of  the  cord  widens 
out  and  forms  the  fourth  ventricle. 
Some  of  the  cranial  nerves  come 
out  from  the  medulla,  and  serve  as 
boundaries  to  describe  the  different 
portions  of  the  medulla.  That  por- 
tion of  white  matter  between  the 
anterior  median  fissure  and  the 
roots  of  the  hypoglossal  nerve  is 

the  anterior  pyramid.  The  lat- 
prnl  pommn  i«s  hpfwppii  flip  rnnt^ 
OI  the  hypoglossal  and  those  OI 

the    glossopharyngeal,    the    pneu- 

/    P  .      , 

mogaStriC,    and    the    Spinal    acces-      and   3,   the    inferior  maxillary   divi- 

SOry.       At    the    upper    portion   the      sions;   VI,  the  left  abducens  nerve; 

!  .  J         i     J      v       i  ,1  i        VII.   VIII,   the  facial  and   auditory 

olivary  body  lies  between  the  col-     ner;es  .  jx-xi,  the  glossopharyngeal, 

limn  and  the  pyramid.      The  pOS-      pneumogastric,  and   spinal   accessory 

terior  column  is  between  the  lat-     ^^K^ci 

eral   column  or  tract  and  the   pOS-      cervical  nerve  (Nancrede). 

terior  median  fissure.  It  is  com- 
posed of  three  smaller  columns  separated  by  shallow  grooves,  the 
most  external  being  the  funiculus  of  Rolando,  next  the  funiculus 
cuneatus,  and  the  most  internal  the  funiculus  gracilis,  the  first 
two  being  joined  in  the  upper  part  of  the  medulla  to  form  the 
restiform  body.  The  outer  portion  of  .the  pyramid  is  derived 


FIG.  279.— View,  from  below,  of  the 
connection  of  the  principal  nerves 
with  the  brain :  I',  the  right  olfactory 
tract ;  II,  the  left  optic  nerve ;  II',  the 
right  optic  tract  (the  left  tract  is  seen 


III,  the  left  oculomotor  nerve  ;  IV,  the 
trochlear;  V,V,  the  large  roots  of  the 
trifacial  nerves:  +  +,  the  lesser  roots 
(the  +  of  the  right  side  is  placed  on 
the  Gasserian  ganglion)  ;  1,  the  oph- 
thalmic;  2,  the  superior  maxillary; 


486  THE  NERVOUS  SYSTEM. 

from  the  direct  pyramidal  tracts  of  the  same  side,  while  the  decus- 
sation  consists  of  the  libers  of  the  crossed  pyramidal  tract  of  the 
lateral  column. 

In  the  restiform  bodies  are  to  be  found,  besides  the  funiculus 
of  Rolando  and  the  funiculus  cuneatus,  fibers  of  the  direct  cere- 
bellar  tract  of  the  lateral  column.  These  bodies  form  the  inferior 
peduncles  of  the  cerebellum.  The  funiculus  of  Rolando  is  the 
enlarged  head  of  the  posterior  cornu  of  the  cord,  and  is  therefore 
gray  matter.  The  funiculus  cuneatus  is  the  continuation  of 
Burdach's  column  of  the  cord,  and  the  funiculus  gracilis  is  the 
continuation  of  GolPs  column. 

Functions  of  the  Medulla  Oblongata. — Conduction. — All  the 
impulses,  whether  afferent  or  efferent,  passing  between  the  brain 
and  the  cord  must  pass  through  the  medulla. 

Nerve-centers. — Experiments  have  demonstrated  that  all  the 
brain  above  the  medulla  and  all  the  spinal  cord  may  be  removed 
and  yet  life  be  maintained,  provided  that  the  origin  of  the  phrenic 
nerves  is  left  intact;  while  if  all  these  structures  are  undisturbed 
and  the  medulla  is  destroyed,  death  will  result.  The  centers  in 
the  medulla  are  both  reflex  and  automatic. 

Reflex  Centers. — One  of  the  most  important  of  these  centers  is 
that  which  presides  over  deglutition.  As  has  been  seen  in  dis- 
cussing this  process,  the  first  stage  of  the  act  is  voluntary ;  but 
as  soon  as  the  food  has  passed  into  the  pharynx,  the  act  becomes 
involuntary.  The  mucous  membrane  of  the  pharynx  is  stimu- 
lated by  the  food,  and  the  afferent  fibers  of  the  glossopharyngeal 
transmit  the  impulse  to  the  medulla,  in  which  a  motor  impulse  is 
generated,  and  out  along  the  efferent  fibers  comes  the  impulse  to 
the  constrictors  of  the  pharynx.  Centers  for  vomiting,  coughing, 
sucking,  and  for  other  movements  are  described. 

The  act  of  vomiting  is  a  reflex  one,  in  which  the  fibers  of  the 
pneumogastric  serve  as  afferent  fibers,  the  impulses  stimulating 
the  center  in  the  medulla,  from  which  emanate  motor  impulses 
to  the  respiratory  and  other  muscles  concerned  in  the  act.  If  the 
act  of  vomiting  is  brought  on  by  stimulating  the  pharynx  with  a 
feather  or  with  a  finger,  the  glossopharyngeal  is  the  carrier  of  the 
afferent  impulses.  Afferent  impulses  producing  vomiting  may  also 
come  from  other  organs,  such  as  the  kidneys,  or  the  testicles  when 
injured. 

Central  Vomiting. — In  central  vomiting  the  center  is  stimu- 
lated by  impulses  which  come  from  the  cerebrum. 

^  Merycism,  or  Rumination. — The  power  to  ruminate,  by  virtue 
of  which  animals  chew  the  cud,  is  possessed  by  some  human  in- 
dividuals, who  can  regurgitate  the  food  whenever  they  feel  so 
disposed,  and  chew  it  again. 

Automatic  Centers. — Besides  reflex  centers,  which  require  a 
stimulus  from  without  to  bring  them  into  action,  the  medulla 


THE  BRAIN.  487 

possesses  automatic  centers  which  generate  and  emit  impulses 
independently  of  stimuli  from  without. 

Respiratory  Center. — This  center  is  situated  in  the  floor  of  the 
fourth  ventricle,  and  when  injured,  respiration  ceases  immediately. 
Some  authorities  place  it  among  the  reflex  centers.  It  may,  in- 
deed, be  excited  reflexly,  but  there  are  reasons  for  believing  it  to 
possess  automatic  powers  as  well.  If  the  spinal  cord  is  divided 
below  the  medulla,  although  the  respiratory  movements  of  the 
thorax  cease,  those  of  the  nose  and  larynx  continue.  Under  these 
circumstances  no  afferent  impulses  can  be  transmitted  through 
the  spinal  nerves,  and  the  only  channel  is  the  cranial  nerves ; 
but  if,  while  the  medulla  and  cord  are  left  undisturbed,  the 
cranial  nerves  are  cut,  respiration  continues.  These  two  series 
of  experiments  show  that  respiration  will  continue  independently 
of  stimuli  from  without — that  is,  automatically. 

The  principal  nerves  that  transmit  the  efferent  impulses  pro- 
ducing the  respiratory  movements  are  the  intercostals  to  the  inter- 
costal muscles,  and  the  phrenics  to  the  diaphragm.  The  respiratory 
center  is  double,  so  that  one  side  may  act  after  the  other  is  injured. 
Division  of  one  phrenic  paralyzes  only  the  side  of  the  diaphragm 
to  which  it  is  distributed.  The  respiratory  center  may  also  be  ex- 
cited reflexly.  The  afferent  fibers  under  these  circumstances  are 
those  of  the  pneumogastric. 

Cardio-inhibitory  Center. — In  the  cardio-inhibitory  center  are 
generated  those  impulses  which,  travelling  to  the  heart  by  the 
vagus  nerve,  inhibit  or  restrain  the  action  of  that  organ.  These 
fibers  convey  impulses  to  the  heart  and  to  the  muscular  fibers  of 
the  superior  vena  cava,  some  of  which  diminish  the  frequency  of 
the  heart's  action,. while  others  lessen  the  strength  of  its  contrac- 
tions. This  center  can  be  stimulated  directly,  as  when  the  blood 
is  very  venous  or  when  the  blood-pressure  in  the  cerebral  arteries  is 
increased.  It  may  also  be  stimulated  reflexly,  as  when  the  sensory 
nerves  of  the  abdominal  viscera  are  irritated,  as  is  shown  in  Goltz's 
percussion  experiment,  by  percussion  of  the  abdomen  of  a  frog. 

Cardio-accelerator  Center. — Fibers  from  this  center,  whose  ex- 
istence is  not  absolutely  demonstrated,  convey  impulses  to  the 
heart  which  increase  the  frequency  of  its  beats,  and  there  are  also 
fibers  which  transmit  impulses  that  increase  the  force  of  the 
systole.  These  fibers  pass  down  the  spinal  cord  and  thence  into 
the  sympathetic  through  the  communicating  branches  of  the  in- 
ferior cervical  and  the  six  upper  thoracic  nerves. 

Vasomotor  Center. — The  principal  vasomotor  center  is  situated 
in  the  medulla,  in  the  floor  of  the  fourth  ventricle,  extending  from 
its  upper  part  to  a  point  about  4  mm.  from  the  calamus  scriptorius. 
When  the  center  is  destroyed  there  is  a  marked  fall  in  arterial 
blood-pressure,  due  to  the  loss  of  tone  in  the  small  blood-vessels. 
After  a  while  the  pressure  is  increased  under  the'  influence  of 
stimuli  sent  out  from  the  subsidiarv  vasomotor  centers  in  the  oord. 


488  THE  NERVOUS  SYSTEM. 

When  the  center  is  stimulated,  arterial  pressure  is  increased  on 
account  of  the  constriction  of  the  vessels. 

Vasomotor  Nerves. — The  vasomotor  nerves,  which  originate  in 
the  cells  of  the  vasomotor  center  in  the  bulb,  pass  down  the  lateral 
column  of  the  spinal  cord,  and  it  is  believed  that  they  arborize 
around  the  cells  of  the  subsidiary  centers  in  the  spinal  cord, 
although  the  precise  location  of  these  centers  has  not  been  deter- 
mined. The  cells  in  these  subsidiary  centers  give  rise  to  axis- 
cylinders  which  form  a  part  of  medullated  nerve-fibers  that  enter 
as  component  parts  of  the  anterior  roots  of  the  spinal  nerves. 

Vasoconstrictor  Nerves. — These  nerves  carry  impulses  which 
cause  constriction  of  the  arterioles.  They  pass  out  from  the  cord 
in  the  anterior  roots  of  the  spinal  nerves  from  the  second  thoracic 
to  the  second  lumbar,  which  they  leave  by  the  white  rami  com- 
municantes,  passing  into  the  sympathetic  ganglia  situated  along  the 
vertebral  column.  These  ganglia  contain  cells  around  which  the 
nerve-fibers  arborize,  and  they  are  spoken  of  as  cell  stations.  From 
these  cells  axis-cylinder  processes  are  given  off  which  are  continued 
as  non-medullated  fibers  and  which  carry  the  impulses  that  orig- 
inate in  the  vasomotor  centers. 

Vasodilator  Nerves. — The  description  of  the  vasoconstrictor 
fibers  just  given  applies  in  general  to  the  vasodilator,  though  there 
are  some  marked  exceptions,  for  while,  as  a  rule,  they  pass  out 
together,  still  some  do  not.  A  striking  example  of  this  is  the 
chorda  tympani,  which  is  given  off  from  the  facial.  Nor  do  the 
dilator  nerves  arborize  around  the  cells  of  the  ganglia  of  the 
sympathetic  chain,  but  pass  through  these  and  lose  their  medullary 
sheaths  in  the  collateral  ganglia,  such  as  the  semilunar,  around 
whose  cells  they  arborize. 

Depressor  Nerve-fibers. — Between  the  heart  and  the  medulla 
are  nerve-fibers  which  carry  impulses  from  the  heart  to  the  vaso- 
motor nerve-center,  which  impulses  inhibit  the  center,  and  thus 
diminish  the  impulses  to  the  muscular  coat  of  the  arteries,  thereby 
causing  the  arteries  to  dilate  and  reducing  arterial  pressure.  In 
the  rabbit  these  fibers  are  together  and  form  the  depressor  nerve, 
but  in  most  animals  they  are  joined  with  the  fibers  of  the  pneumo- 
gastric.  By  means  of  these  fibers  the  nerve-center  can  be  inhibited 
and  arterial  pressure  lessened,  thus  reducing  the  work  of  the 
heart. 

Pons  Varolii. — The  pons  Varolii  (tuber  annulare  or  meso- 
cephalon)  is  situated  just  above  the  medulla,  and  is  composed 
of  three  sets  of  fibers  and  of  some  gray  matter.  The  first  set 
consists  of  superficial  transverse  fibers  which  cross  the  upper 
part  of  the  medulla  and  connect  the  two  hemispheres  of  the  cere- 
bellum, forming  at  the  sides  the  crura  cerebelli  or  middle 
peduncles.  The  second  is  made  up  of  longitudinal  fibers  which 
come  from  the  pyramids  of  the  medulla  and  pass  on  to  help  form 
the  crura  cere_bri.  The  third  set  is  also  transverse  and  is  deeply 


THE  BRAIN. 


489 


situated,    connecting   the   middle    peduncles   of    the   cerebellum. 
Among  its  fibers  are  collections  of  gray  matter. 

Functions  of  the  Pons  Varolii. — The  anatomic  relations  of  the 
pons  show  that  it  must  serve  as  a  conductor  of  impulses  both  to 
and  from  the  centers  above.  As  to  the  function  of  its  gray  matter, 
comparatively  little  is  known,  save  that  from  a  portion  of  it  some 
of  the  cranial  nerves  arise.  If  it  is  stimulated  or  divided,  pain 
and  spasms  are  produced.  When  a  lesion  is  situated  in  the  lower 
half  of  the  pons,  there  result  facial  paralysis  on  the  same  side  as 
the  lesion,  and  motor  and  sensory  paralysis  on  the  opposite  side 
of  the  body.  This  is  called  alternate  paralysis.  If  the  lesion  is 
in  the  upper  half  of  the  pons,  the  facial  paralysis  and  that  of  the 
body  are  on  the  same  side.  When  the  pons  is  suddenly  and  ex- 
tensively injured,  a  condition  of  hyperpyrexia  is  often  produced, 
the  temperature  rising  rapidly  within  an  hour.  This  is  probably 


M)endrite. 


Blood-vessel. -V— — 


^0:  -    '     -f«-  r  ..-        c     .»-  ?  -o^ .  Nerve-fiber 

^  layer. 

4;  -~*-"" •••"—•-i-  •  •  j 

FIG.  280. — Section  through  the  human  cerebellar  cortex  vertical  to  the  surface  of 
the  convolution;  treatment  with  Miiller's  fluid;  x  115  (Bohrn  and  Davidoff). 

due  to  the  influence  of  the  gray  matter  in  the  floor  of  the  fourth 
ventricle,  or  possibly  to  the  involvement  of  some  special  heat- 
regulating  center. 


I 


THE  BRAIN. 


491 


The  Cerebellum.— The  cerebellum  (Figs.  280,  281)  is  com- 
posed externally  of  gray  matter,  which  also  penetrates  into  the 
substance  of  the  organ,  forming  with  the  white  matter  the  laminae. 
In  the  central  part  of  the  cerebellum  is  white  matter,  in  which  is 
imbedded  a  collection  of  gray  matter,  the  corpus  'dentatum.  The 
cerebellum  is  connected  with  the  rest  of  the  encephalon  by  the 
superior,  the  middle,  and  the  inferior  peduncles.  The  superior 
peduncles  (processus  e  cerebello  ad  testes)  connect  the  cerebellum 
with  the  cerebrum ;  the  middle  peduncles  (crura  cerebelli)  con- 
nect the  two  cerebellar  hemispheres;  the  inferior  (processus  ad 
medullam)  connect  the  cerebellum  and  medulla  oblongata. 

The  gray  matter  consists  of  two  layers,  an  inner  or  granular 
layer,  composed  of  nerve-cells,  principally  small  in  size,  and 
neuroglia ;  and  an  outer  or  molecular  layer,  composed  of  fine  nerve- 
fibers  and  nerve-cells.  Between  these  two  layers  are  the  cells 
of  Purkinje,  which  are  flask-shaped,  and  from  the  base  of  each  of 
which  is  given  off  a  neuron,  which  is  continued  as  an  axis-cylinder 


Dendrite. 


Cell-bod  v. 


Neuraxis. 


Neuraxis. 


FIG.  282.— Cell  of  Purkinje  from  the  human 
cerebellar  cortex ;  chrome-silver  method ;  X  120 
(Bohm  and  Davidoff). 


—  Claw-like  telo- 
dendron  of 
dendrite. 


FIG.  283.— Granular  cell 
from  the  granular  layer  of 
the  human  cerebellar  cortex ; 
chrome-silver  method;  x  100 
(Bohm  and  Davidoff). 


of  a  medullated  nerve-fiber  of  the  white  center.  From  the  opposite 
side  are  given  off  dendrons  which  pass  into  the  gray  matter.  In 
discussing  the  structure  of  the  cerebellum,  Schafer  says :  "  The 
dendrons  of  the  cells  of  Purkinje  spread  out  in  planes  trans- 
verse to  the  lamellae  of  the  organ,  so  that  they  present  a  different 
appearance  according  to  whether  the  section  is  taken  across  the 


492  THE  NERVOUS  SYSTEM. 

lamellae  or  along  them.  These  dendrons  are  invested  at  their 
attachment  to  the  cell,  and  to  some  extent  along  their  branchings, 
by  basketworks  formed  by  the  terminal  arborizations  of  certain 
fibers  of  the  medullary  center.  The  body  of  the  cell  of  Purkinje 
is  further  invested  by  a  feltwork  of  fibrils  formed  by  the  arboriza- 
tion of  axis-cylinder  processes  of  the  same  nerve-cells  in  the  outer 
layer  of  the  gray  matter.  Each  cell  has  therefore  a  double  invest- 
ment of  this  nature,  one  covering  the  dendrons,  the  other  the  body 
of  the  cell.  Ramifying  among  the  granule-layer  are  peculiar 
fibers  derived  from  the  white  center,  and  characterized  by  having 
pencils  of  fine  short  branches  at  t intervals  like  tufts  of  moss. 
These  are  termed  by  Cajal  the  moss-fibers;  they  end  partly  in  the 
granule-layer,  partly  in  the  molecular  layer." 

Functions  of  the  Cerebellum. — If  the  surface  of  the  cerebellum 
is  irritated,  no  muscular  movements  are  produced,  nor  is  there  any 
evidence  of  sensation  ;  if,  however,  the  irritation  is  applied  near 
the  medulla  or  inferior  peduncles,  both  pain  and  muscular  contrac- 
tion result.  If  the  cerebellum  is  removed  wholly  or  partially, 
sensation  is  not  diminished  in  the  part  of  the  body  below,  nor  is 
there  any  impairment  of  the  power  of  producing  muscular  move- 
ments, nor  of  the  special  senses,  nor  of  the  intelligence ;  but  there 
is  a  marked  want  of  harmony  in  the  muscular  movements — a  lack 
of  co-ordination.  Attention  has  already  been  called  to  the  fact 
that  even  the  simplest  movements  that  are  made  require  the 
harmonious  action  of  different  muscles,  and  when  these  move- 
ments are  more  complex,  they  require  different  sets  of  muscles. 
If  these  movements  do  not  occur  at  just  the  right  time  and  are 
not  produced  in  the  right  manner,  the  result  is  disorder  instead 
of  harmony ;  or,  as  it  is  expressed,  there  is  a  want  of  co-ordina- 
tion, or  a  condition  of  inco-ordination  or  cerebellar  ataxy.  This 
is  the  effect  of  removing  the  cerebellum.  Thus,  if  the  cerebellum 
of  a  pigeon  is  removed,  and  an  attempt  is  then  made  by  it  to 
fly,  it  is  unsuccessful,  for  this  act  requires  the  consentaneous  action 
of  both  wings,  which  action  is  absent.  In  walking  the  bird  reels 
like  a  person  intoxicated,  and  cannot  go  to  the  spot  for  which  it 
apparently  set  out.  It  should  be  borne  in  mind  that  there  is  no 
paralysis  either  of  motion  or  of  sensation  in  this  condition,  but 
the^  voluntary  movements  which  originate  in  the  cerebrum,  and 
which  are  in  the  normal  condition  co-ordinated  by  the  cerebellum, 
pass  to  the  muscles  without  this  regulating  influence,  and  the 
result  is  a  series  of  disordered  movements. 

Especially  marked  is  this  inco-ordination  in  connection  with 
the  maintenance  of  the  equilibrium*  of  the  body  and  locomotion. 
Indeed,  some  authorities  are  inclined  to  limit  the  functions  of 
the  cerebellum  to  this,  and  to  regard  it  as  not  being  the  con- 
trolling organ  of  co-ordination  in  general,  quoting  experiments 
upon  animals  in  which,  after  the  first  effects  of  its  removal  had 
passed  away,  there  was  a  return  of  the  co-oHinating  power, 


THE  BRAIN.  493 

and  also  instances  in  the  human  subject  in  which  during  life 
the  movements  had  been  co-ordinated,  yet  after  death  the  cere- 
bellum had  been  found  completely  disorganized. 

It  is  interesting  to  know  that  in  animals  that  produce  complex 
movements  {he  cerebellum  is  considerably  developed,  while  in 
those  whose  movements  are  simple,  such  as  the  frog,  this  organ 
is  exceedingly  small. 

Sources  of  Impressions  that  reach  the  Cerebellum. — The  ana- 
tomic relations  of  the  cerebellum  are  so  intimate  that  impressions 
of  many  kinds  can  reach  it  and  thus  enable  it  to  preside  over  this 
most  important  function  of  co-ordination,  especially  as  regards 
equilibration  and  locomotion. 

Equilibration. — Sewall  defines  equilibrium  as  "a  state  in  which 
all  the  skeletal  muscles  are  under  control  of  nerve-centers,  so  that 
they  combine,  when  required,  to  resist  the  effect  of  gravity  or  to 
execute  some  co-ordinated  motion."  In  order  that  these  centers 
may  send  to  the  muscles  of  the  body  impulses  that  are  adapted 
to  produce  the  desired  result,  it  is  absolutely  essential  that  they 
should  receive  impressions  which  will  give  them  cognizance  of  the 
exact  position  of  the  body  and  of  the  condition  of  the  muscles  at 
the  moment  as  to  contraction  or  relaxation.  These  impressions  or 
sensations  taken  as  a  whole  constitute  the  sense  of  equilibrium, 
and  while  it  is  doubtless  true  that  all  sensations  contribute  to 
bring  about  this  result,  yet  there  are  some  which  are  more  directly 
concerned  than  others.  These  are  impulses  received  from  the 
skin,  from  the  muscles,  and  from  the  semicircular  canals,  the  last 
being  doubtless  the  most  important. 

Impressions  from  the  Semicircular  Canals. — These  are  some- 
times described  under  the  name  labyrinthine  impressions.  For  a 
description  of  the  labyrinth,  the  reader  is  referred  to  page  607. 

Although  in  intimate  anatomic  relationship  with  the  organs  of 
hearing,  there  is  still  no  doubt  that  the  semicircular  canals  bear 
no  physiologic  relationship  with  that  special  sense,  for  removal  of 
these  structures  leaves  hearing  unimpaired,  provided,  of  course, 
the  cochlea?  are  uninjured.  On  the  other  hand,  serious  disturbances 
of  equilibrium  do  result,  and  these  vary  according  as  one  or 
another  of  the  canals  is  destroyed.  Thus,  if  in  a  pigeon  the 
horizontal  canal  is  destroyed,  the  bird  moves  its  head  from  side  to 
side  around  a  vertical  axis :  whereas  if  the  injury  is  to  the 
superior  canal,  the  movements  are  vertical  around  a  horizontal 
axis.  When  a  pigeon  whose  semicircular  canals  have  been  injured 
is  in  a  resting  posture,  it  stands  with  its  head  turned  backward  or 
forward  or  to  one  side,  never  in  a  natural  position  ;  and  when  dis- 
turbed, its  movements  are  irregular,  accompanied  by  rolling  of  the 
eyes  and  an  inability  to  fly.  If  the  injury  is  limited  to  one  side, 
recovery  soon  takes  place ;  while  if  the  canals  on  both  sides  are 
destroyed,  the  condition  is  a  more  persistent  one.  Different  ani- 
mals act  somewhat  differently  after  injury  to  the  canals ;  in  mam- 


494 


THE  NERVOUS  SYSTEM. 


rnals  the  movements  described  affect  the  eyes  rather  than  the 
head. 

The  explanation  of  the  manner  in  which  the  canals  are  con- 
cerned with  equilibrium  is  that  any  change  in  the  pressure  of  the 
eudolymph  upon  the  hair-cells  of  the  cristae  acusticse  in  the  am- 
pullae of  the  semicircular  canals  will  produce  a  change  in  the  sen- 
sations which  reach  the  center  presiding  over  equilibration — L  e., 
probably  the  middle  lobe  of  the  cerebellum. 

It  will  be  seen  by  a  reference  to  Fig.  284  that  the  canals  are 


FIG.  284. — Diagram  of  semicircular  canals  to  show  their  positions  in  three  planes 
at  right  angles  to  one  another.  It  will  be  seen  that  the  two  horizontal  canals  (H)  lie 
in  the  same  plane,  and  that  the  superior  vertical  of  one  side  (S)  lies  in  a  plane 
parallel  to  that  of  the  posterior  vertical  (P)  of  the  other  (after  Ewald). 

at  right  angles  to  one  another  and  thus  occupy  the  three  planes  of 
space :  the  horizontal  canal  of  one  side  being  in  the  same  plane 
with  the  corresponding  canal  of  the  other,  and  one  anterior 
vertical  canal  practically  parallel  with  the  opposite  posterior 
vertical  canal.  Thus  movements  of  the  head  cause  an  increase 
of  the  pressure  of  the  endolymph  in  one  ampulla  and  a  decrease 

in  that  of  its  parallel  canal  on 
the  other  side,  and  the  sensory 
impressions  thus  produced  are 
at  once  transmitted  to  the  center. 
When  a  canal  is  injured,  its  endo- 
lymph is  drained  off,  and  at  once 
there  is  an  interference  with  the 
pressure  upon  the  hair-cells,  to- 
gether with  a  consequent  modifica- 
tion of  the  normal  impressions. 
FIG.  285. — Diagrammatic  hori-  ^x,  .  £ 

zontal  section  through  the  head  to  Observation  upon  man  connrms 
illustrate  the  planes  occupied  by  these  experiments  upon  the  lower 
": 'jSUXrM  H,Pho£  animals.  _  Thus  a  man  with  his  eyes 

zontal  canal  (after  Waller).  closed   lying   upon  a  table  which  IS 

rotated,  can  tell   that  he  is  being 

moved,  in  what  direction,  and  to  some  extent  through  how  great 
an  angle ;  and  when  the  rotation  ceases  the  sensation  of  rotation 
in  the  opposite  direction  is  experienced.  In  deaf-mutes,  in  whom 


THE  BRAIN. 


495 


this  condition  is  due  to  a  defect  in  the  internal  ear,  there  is  an 
absence  of  the  dizziness  experienced  by  normal  individuals  when 
rapidly  rotated  in  a  swing.  The  vertigo  of  MeniZre's  disease  is 
accompanied  by  changes  in  the  internal  ear.  It  has  also  been 
observed  that  defects  of  locomotion  and  equilibration  are  more 
common  in  deaf  and  dumb  children  than  in  those  that  are  normal. 
Static  Equilibrium. — By  this  term  is  meant  the  equilibrium  of 
rest,  and  Lee  regards  the  utricle  and  saccule  as  being  the  organs 
concerned  in  this  function.  That  is,  that  the  knowledge  of  the 
position  of  the  head  while  at  rest  is  communicated  to  the  co-ordi- 
nating center  in  the  cerebellum  by  the  pressure  of  the  endo- 


FIG.  286. — View  of  the  brain  from  above :  A,  anterior  central  or  ascending 
frontal  convolution ;  B,  posterior  central  or  ascending  parietal  convolution  ;  C,  cen- 
tral fissure,  or  fissure  of  Rolando ;  cm,  callosomarginal  sulcus ;  F,  frontal  lobe ;  Fi, 
upper,  Fz,  middle,  Fs,  lower  frontal  convolution ;  f\,  superior  frontal  sulcus ;  /2, 
inferior  frontal  sulcus ;  /s,  vertical  fissure  (sulcus  prsecentralis) ;  ip,  interparietal 
sulcus ;  0,  occipital  lobe ;  o,  sulcus  occipitalis  transversus ;  Oi,  first  occipital  convo- 
lution ;  02,  second  occipital  convolution ;  P,  parietal  lobe ;  po,  parieto-occipital 
fissure ;  Pi,  upper  or  posteroparietal  lobule ;  PJ,  lower  parietal  lobule,  constituted 
by  PJ,  gyrus  supramarginalis ;  P-j ,  gyrus  angularis;  81,  end  of  the  horizontal  branch 
of  the  fissura  Sylvii ;  ti,  upper  temporal  fissure. 

lymph  upon  the  otoliths,  and  these  in  turn  upon  the  hair-cells  of 
the  maculae  acusticae. 

Dynamic  Equilibrium. — This  is  the  equilibrium  of  motion,  and, 
as  already  stated,  is  presided  over  by  the  semicircular  canals, 
from  which  impressions  pass  to  the  cerebellum.  v 

The  Cerebrum. — The  cerebrum,  which  in  man  makes  up 
about  four-fifths  of  the  encephalon,  is  divided  into  two  hemi- 
spheres which  are  separated  by  the  great  longitudinal  fissure  (Figs. 
286-289),  but  are  connected  by  a  white  commissure,  the  corpus 


496 


THE  NERVOUS  SYSTEM. 


callosum.  The  surface  presents  depressions,  fissures  and  sulci, 
and  prominences,  convolutions  or  gyri.  The  external  portion  of 
the  hemispheres  is  gray  nervous  matter  about  3  mm.  in  thickness, 
beneath  which  is  white  matter.  The  fissures  are  not  numerous, 
but  are  quite  constant ;  they  are  folds  of  the  brain-matter  both 
gray  and  white.  The  sulci  are  depressions  of  the  gray  matter 
alone ;  they  are  very  numerous  and  inconstant.  As  gray  matter 
is  present  on  both  sides  of  the  fissures  and  sulci,  this  arrangement 
permits  of  a  larger  amount  of  gray  matter  than  could  exist  were  it 
only  upon  the  surface  of  the  convolutions.  In  a  brain,  therefore, 
where  the  sulci  are  deep  and  numerous  the  amount  of  gray  matter 


FIG.  287. — Outer  surface  of  the  left  hemisphere :  A,  anterior  central  or  ascending 
frontal  convolution ;  B,  posterior  central  or  ascending  parietal  convolution ;  c,  sulcus 
centralis  or  fissure  of  Eolando ;  cm,  termination  of  the  callosomarginal  fissure ;  F, 
frontal  lobe ;  F\,  superior,  l^Vniddle,  and  Fz,  inferior  frontal  convolution  ;  /i,  supe- 
rior, and  /2,  inferior  frontal  sulcus  ;  /a,  sulciu  prsecentralis ;  ip,  sulcus  intraparietalis ; 
0,  occipital  lobe ;  Oi,  first,  Oz,  second,  Os,  third  occipital  convolutions ;  01,  sulcus 
occipitalis  transversus ;  02,  sulcus  occipitalis  longitudinalis  inferior ;  P,  parietal  lobe ; 
po,  parieto-occipital  fissure ;  Pi,  superior  parietal  or  posteroparietal  lobule ;  Pz,  infe- 
rior parietal  lobule,  viz.,  P2,  gyrus  supramarginalis ;  P{,  gyrus  angularis ;  S,  fissure 
of  Sylvius ;  S',  horizontal,  S",  ascending  ramus  of  the  same ;  T,  temporosphenoidal 
lobe:  Tij  first,  Tz,  second,  Ts,  third  temporosphenoidal  convolutions;  ti,  first,  tz, 
second  temporosphenoidal  fissures. 

exceeds  that  in  a  brain  where  they  are  more  shallow  and  less 
abundant.  This  gray  matter  is  the  cortical  substance. 

Fissures  of  the  Cerebrum. — The  fissures  serve  as  landmarks 
in  the  description  of  the  diiferent  parts  of  the  hemispheres. 
Besides  the  great  longitudinal  fissure,  there  are  (1)  the  fissure  of 
Sylvius  ;  (2)  that  of  Rolando  ;  and  (3)  the  parieto-occipital  fissure. 
These  fissures  divide  each  hemisphere  into  5  lobes. 

(1)  The  fissure  of  Sylvius  is,  next  to  the  great  longitudinal 
fissure,  the  most  important.  It  is  found  in  all  animals  whose 
brains  have  any  fissures.  It  exists  in  the  human  brain  in  the 


THE  BRAIN.  497 

third .  month  of  intra-uterine  life.  It  commences  at  the  base  of 
the  brain,  and  runs  .outward,  backward,  and  upward,  giving  off  a 
short  anterior  branch  or  limb.  The  continuation  of  the  fissure 
backward  from  where  this  branch  is  given  off  is  the  posterior 
branch  or  horizontal  limb,  which  ends  in  the  parietal  lobe.  The 
fissure  of  Sylvius  is  the  boundary  between  the  frontal  and  parietal 
lobes  on  the  one  hand  and  the  temporosphenoidal  on  the  other. 
At  the  middle  and  anterior  part  of  this  fissure,  deeply  situated,  is 
the  island  of  Reil,  or  insula,  or  central  lobe. 

(2)  The  fissure  of  Rolando  starts  near  the  median  line,  and  runs 
downward  and  forward  nearly  to  the  fissure  of  Sylvius.  It  is 
the  boundary  between  the  frontal  and  parietal  lobes. 


FIG.  288.— Inner  surface  of  right  hemisphere :  A,  ascending  frontal ;  B,  ascend- 
ing parietal  convolution ;  c,  terminal  portion  of  the  sulcus  centralis,  or  fissure  of 
Eolaudo;  (7(7,  corpus  callosum,  longitudinally  divided;  Cf,  collateral  or  occipito- 
temporal  fissure  (Ecker) ;  cm,  sulcus  callosomarginalis ;  D,  gyrus  descendens ;  Fi, 
median  aspect  of  the  first  frontal  convolution  ;  (?/,  gyrus  fornicatus ;  H,  gyrus  hip- 
pocampi ;  h,  sulcus  hippocampi,  or  dentate  fissure;  0,  sulcus  occipitalis  transversus; 
oc,  calcarine  fissure ;  oc',  superior,  oc",  inferior  ramus  of  the  same ;  Oz,  cuneus  ;  po, 
parieto-occipital  fissure;  Pi",  precuneus ;  Tt,  gyrus  occipitotemporalis  lateralis 
(lobulus  fusiformis) ;  Ts,  gyrus  occipitotemporalis  medialis  (lobulus  lingualis) ;  U, 
uncinate  gyrus. 

(3)  The  parieto-occipital  fissure  is  about  half-way  between  the 
fissure  of  Rolando  and  the  posterior  extremity  of  the  brain,  and 
is  the  boundary  between  the  parietal  and  occipital  lobes. 

Lobes  of  the  Cerebrum. — The  lobes  of  the  cerebrum  are  (1)  the 
frontal,  (2)  the  parietal,  (3)  the  occipital,  (4)  the  temporosphen- 
oidal, and  (5)  the  central,  or  island  of  Reil. 

(1)  The  frontal  lobe  is  above  the  fissure  of  Sylvius  and  in  front 
of  the  fissure  of  Rolando.  It  is  divided  into  4  convolutions  by 
3  sulci,  or  fissures  as  they  are  sometimes  called.  The  precentral 
fissure  or  sulcus  is  in  front  of  the  fissure  of  Rolando,  and  the 
convolution  between  the  two  is  the  ascending  frontal.  From  the 
upper  extremity  of  this  sulcus  the  superior  frontal  sulcus  runs 
downward  and  forward  between  the  superior  and  middle  frontal 

32 


498 


THE  NERVOUS  SYSTEM. 


convolutions,  while  from  the  lower  extremity  extends  the  inferior 
frontal  sulcus,  separating  the  middle  and  inferior  frontal  convolu- 
tions. Thus  the  frontal  lobe  is  divided  into  the  ascending, 
superior,  middle,  and  inferior  frontal  convolutions. 

(2)  The  parietal  lobe  is  behind  the  frontal  and  in  front  of  the 
occipital  lobe,  the  fissure  of  Rolando  being  its  anterior,  and  the 
parieto-occipital    fissure    its    posterior    boundary.      Its    inferior 
boundary  is  the  fissure  of  Sylvius  and  the  imaginary  continuation 
of  it  to  the  superior  occipital  sulcus.     It  has  2  sulci,  the  intra- 
parietal  and  the  post-central,  and  3  convolutions,  the  ascending, 
superior,  and  inferior  parietal. 

(3)  The  occipital  lobe  is  posterior  to  the  parietal,  and  has  2 


Lobulus  paracentralis, 


FIG.  289.— Lateral  view  of  the  brain :  gyri  and  lobuli  marked  with  antique  type, 
the  sulci  and  fissures  with  italic  type  (combined  from  Ecker). 

sulci,  the  superior  and  middle,  and  3  convolutions,  the  superior, 
middle,  and  inferior  occipital,  the  latter  being  subdivided  into  the 
supramarginal  and  the  angular. 

(4)  The  Temporosphenoidal  Lobe. — The  fissure  of  Sylvius  forms 
the  anterior  and  superior  boundaries  of  this  lobe,  while  its  posterior 
boundary  is   the   imaginary  continuation  of  the  occipitoparietal 
fissure.     It  presents  2  sulci,  the  superior  temporosphenoidal  or 
parallel,  and  the  middle  temporosphenoidal.     Its  convolutions  are 
3,  the  superior,  middle,  and  inferior  temporosphenoidal. 

(5)  The  central  lobe,  or  island  of  Reil,  is  situated  at  the  base  of 
the  brain,  in  the  fissure  of  Sylvius.     It  consists  of  6  convolutions, 
the  gyri  operti. 


THE  BRAIN.  499 

Crura  cerebri,  also  called  the  peduncles  of  the  cerebrum,  are 
made  up  of  white  matter,  nerves  which  are  continuous  with  those 
already  studied  in  the  medulla  and  pons,  together  with  nerves 
from  the  cerebellum,  the  superior  peduncles.  Between  the  super- 
ficial fibers  of  the  crura,  the  crusta,  and  the  deeper  ones,  the  teg- 
mentumf  is  the  locus  niger,  a  collection  of  gray  matter.  The 
fibers  of  the  crura  on  their  way  upward  to  the  gray  matter  of  the 
hemispheres  pass  through  the  corpora  striata  and  the  optic 
thalami. 

Basal  Ganglia. — At  the  base  of  the  hemisphere  are  certain 
bodies,  the  basal  ganglia,  which  are  the  corpora  striata,  the  optic 


co. 


FIG.  290.— Vertical  section  through  the  cerebrum  and  basal  ganglia  to  show  the 
relations  of  the  latter:  co.,  cerebral  convolutions;  c.c.,  corpus  callosum;  v.l.,  lateral 
ventricle ;  6.,  fornix ;  vIIL,  third  ventricle ;  n.c.,  caudate  nucleus ;  th,  optic  thala- 
mus;  n.l.,  lenticular  nucleus;  c.L,  internal  capsule;  cl,  claustrum;  c.e.,  external 
capsule  ;  m,  corpus  mammillare  ;  t.o.,  optic  tract ;  s.t.t.,  stria  terminalis ;  n.a.,  nucleus 
amygdalae;  cm,  soft  commissure ;  co.i,  island  of  Reil  (Schwalbe). 
> 

thalami,  the  tubercula  quadrigemina  or  corpora  quadrigemina,  the 
corpora  geniculata,  and  the  locus  niger. 

Corpora  striata,  with  the  optic  thalami,  are  called  the  cerebral 
ganglia.  The  corpora  striata  present  a  striped  appearance,  which 
is  due  to  a  mixture  of  gray  and  white  matter,  the  latter  being 
bundles  of  fibers  which  have  come  from  below  and  within-. 
Although  at  the  lowest  part  each  corpus  striatum  is  a  single  body, 
at  the  upper  part  it  is  divided  into  two  portions,  the  caudate 
nucleus  and  lenticular  nucleus.  The  lenticular  nucleus,  the  more 
posterior,  is  separated  from  the  optic  thalamus  by  white  matter, 
the  internal  capsule,  which  is  the  continuation  of  the  crus  cerebri. 
Outside  the  lenticular  nucleus  is  white  matter,  the  external  cap- 
sule, beyond  which  is  a  layer  of  gray  matter,  the  claustrum,  and 


500 


THE  NERVOUS  SYSTEM. 


external  to  all  these  structures  is  the  island  of  Reil.  The  cortical 
substance  is  at  this  point  very  near  the  gray  matter  of  the  basal 
ganglia. 

The  fibers  of  the  internal  capsule,  passing  upward,  radiate 
forward,  upward,  and  backward,  forming  the  corona  radiata,  the 
fibers  of  which  pass  to  the  cortex,  each  one  being  the  continuation 
of  the  axis-cylinder  process  of  a  pyramidal  cell.  The  fibers  of 
the  internal  capsule  give  off  collaterals  which  pass  to  the  optic 
thalamus,  and  the  nucleus  caudatus  and  nucleus  lenticularis  of 


PCI. 

AP 


FIG.  291. — Diagram  to  show  the  connection  of  the  frontal  occipital  lobes  with  the 
cerebellum:  ec.,  the  dotted  lines  passing  in  the  crusta  (TOO),  outside  the  motor 
fibers,  indicate  the  connection  between  the  temporo-occipital  lobe  and  the  cerebel- 
lum ;  F.  C.,  the  frontocerebellar  fibers,  which  pass  internally  to  the  motor  tract  in 
the  crusta ;  I.F.,  fibers  from  the  caudate  nucleus  to  the  pons  ;  Fr.,  frontal  lobe  ;  Oc., 
occipital  lobe ;  AF.,  ascending  frontal ;  AP.,  ascending  parietal  convolutions  ;  PCF., 
precentral  fissure  in  front  of  the  ascending  frontal  convolution ;  FR.,  fissure  of 
Rolando  ;  IFF.,  interparietal  fissure.  A  section  of  cms  is  lettered  on  the  left  side  : 
S.IV.,  substantia  nigra  ;  PY.,  pyramidal  motor  fibers,  which  on  the  right  are  shown 
as  continuous  lines  converging  to  pass  through  the  posterior  limb  of  /.  C.,  internal 
capsule  (the  knee  or  elbow  of  which  is  shown  thus  (*) )  upward  into  the  hemisphere 
and  downward  through  the  pons  to  cross  at  the  medulla  in  the  pyramidal  decussa- 
tion  ;  Ipt.,  crossed  pyramidal  tract;  apt.,  direct  pyramidal  tract  (Gowers). 

the  corpus  striatum.  These  ganglia  give  off  fibers  which  pass 
into  the  internal  capsule  and  corona  radiata.  There  are,  there- 
fore, fibers  passing  into  these  ganglia  and  others  passing  out 
from  them,  the  latter  being  the  more  numerous.  The  pyramidal 
fibers  in  their  downward  course  thus  give  off  collaterals  which 
arborize  around  the  cells  of  the  corpus  striatum  and  optic  thala- 
mus, and  from  these  ganglia  axis-cylinder  processes  pass  out  to 
form  a  part  of  the  pyramidal  tract.  So,  also,  the  sensory  fibers, 
particularly  those  of  the  fillet,  arborize  around  the  cells  of  the 
optic  thalamus  and  the  subthalamic  region. 


THE  BRAIN.  501 

It  is  in  this  locality  that  hemorrhage  produces  such  serious 
consequences.  The  blood-vessels  supplying  the  basal  ganglia 
may  rupture  on  account  of  a  diseased  condition,  and  as  a  result  of 
this  apoplexy  or  paralysis  may  occur,  or  the  hemorrhage  may  prove 
fatal.  When  the  hemorrhage  takes  place  into  the  anterior  portion 
of  the  internal  capsule,  hemiplegia,  or  paralysis  of  motion  in  the 
opposite  side  of  the  body,  will  -result ;  while  if  it  is  into  the  poste- 
rior part,  paralysis  of  sensation  will  occur  on  the  opposite  side. 

Optic  Thalami  (Fig.  290). — Each  of.  these  bodies  is  covered 
by  a  layer  of  white  fibers,  which  is  especially  prominent  in  the 
internal  capsule.  From  the  capsule  it  enters  the  thalamus,  con- 
necting it  with  the  hemisphere.  The  gray  matter  of  the  thalamus, 
of  which  it  is  principally  composed,  is  aggregated  into  two  masses, 
an  outer  and  an  inner  nucleus,  separated  by  a  white  lamina,  the 
internal  medullary  lamina.  In  the  anterior  portion  there  is  a  third 
portion  of  gray  matter,  in  which  the  nerve-cells  are  quite  large. 
The  cells  of  the  thalamus  are  multipolar  and  fusiform. 

Corpora  Quadrigemina. — These  bodies,  4  in  number,  the  ante- 
rior pair  being  the  testes,  and  the  posterior  the  nates,  are  situated 
behind  the  third  ventricle  and  posterior  commissure  and  under 
the  posterior  border  of  the  corpus  callosum.  They  consist 
principally  of  gray  matter.  Each  gives  off  a  bundle  of  white 
fibers  to  the  corpora  geniculata,  which  joins  the  optic  tract  of 
the  same  side,  and  each  receives  fibers  of  the  fillet  which  can  be 
traced  to  nuclei  of  the  opposite  funiculus  gracilis  and  cuneatus. 
Thus  the  fillet  serves  as  a  channel  for  afferent  impulses  which 
have  traversed  the  fibers  of  the  posterior  roots  of  the  spinal 
nerves.  These  nerves  arborize  around  the  cells  of  the  nuclei, 
from  which  the  fibers  of  the  fillet  arise.  Over  the  gray  matter  of 
the  superior  corpora  quadrigemina  is  a  layer  of  nerve-fibers  which 
have  their  origin  in  the  nerve-cells  of  the  retina,  coming  by  way 
of  the  optic  tract,  and  which  pass  into  the  corpora  quadrigemina 
and  arborize  around  the  cells  of  the  gray  matter.  Schafer  says 
that  these  cells  "are  very  various  in  form  and  size,  and  are  dis- 
posed in  several  layers,  which  are  better  seen  in  the  optic  lobe  of 
the  bird  (Fig.  292)  than  in  mammals.  Most  of  their  processes 
pass  ventralward.  Their  destination  is  not  certainly  known,  but 
some  appear  to  pass  downward  with  the  fillet,  others  probably 
turn  upward  and  run  in  the  tegmentum  toward  the  higher  parts 
of  the  brain ;  while  others,  perhaps  most,  probably  form  terminal 
arborizations  around  the  motor  cells  of  the  oculomotor  and  other 
motor  nuclei.  All  the  nerve-fibers  of  the  optic  nerve  and  optic 
tract  do  not  enter  the  corpora  quadrigemina.  Some  pass  into  the 
lateral  geniculate  bodies  and  form  arborizations  there.  On  the 
other  hand,  from  the  cells  of  these  geniculate  bodies  the  axis- 
cylinder  processes  appear  to  pass  to  the  cortex  of  the  brain 
(occipital  region)." 


502 


THE  NERVOUS  SYSTEM. 


Functions  of  the  Cerebral  Ganglia. — A  marked  change  has  taken 
place  within  comparatively  recent  times  as  to  the  functions  and 
importance  of  the  corpora  striata  and  the  optic  thalami.  The 
former  were  for  a  long  period  of  time  considered  important  motor 
centers,  and  the  latter  as  performing  the  same  role  with  reference 
to  sensation.  This  was  doubtless  largely  due  to  the  fact,  to  which 
Kirkes  calls  attention,  that  when  a  hemorrhage  took  place  in  the 


FIG.  292.— Sections  of  optic  lobe  of  bird 
taken  in  planes  at  right  angles  to  one  another 
(S.  Ramon  y  Cajal)  (Golgi  method). 

A.  Anteroposterior  section  :  a,  optic  fibers 
cut  across.    The  other  letters  indicate  differ- 
ent kinds  of  cells,  of  which  it  will  be  noticed 
that  some  have  their  axis-cylinder  processes 
extending  outward  toward  the   optic  fiber 
layer,  and  others  have  their  axis-cylinder 
processes  extending  inward  toward  a  deep 
layer  of  nerve-fibers ;  s,  some  have  only  short 
neurons  ramifying  in  adjacent  layers. 

B.  Transverse  section :  a,  optic  fibers  cut 
longitudinally;    b,   c,   d,    e,  their  terminal 
ramifications  in  different  layers  of  the  gray 
matter. 


region  of  the  corpora  striata,  motor 
paralysis  was  the  result ;  and  that 
when  it  occurred  in  the  region  of 
the  optic  thalamus,  sensory  paral- 
ysis followed.  It  was,  therefore, 
natural  to  attribute  motion  and 

sensation  to  these  ganglia  respectively.     It  is  now  known  that 

?d  to  these  i 


when  the  hemorrhage  is  limited  to  these  ganglia  paralysis  is  slight, 
or  even  absent  altogether,  and  that  the  effects  of  cerebral  hemor- 
rhage ordinarily  observed  are  due  to  injury  of  the  internal  capsule  ; 
and  hemorrhage  into  the  anterior  portion  is  followed  by  motor 
paralysis,  because  it  is  here  that  the  fibers  pass  which  carry 
motor  impulses  from  the  cortex  to  the  cord ;  and  that  hemorrhage 


THE  BRAIN. 


503 


into  the  posterior  part  is  followed  by  paralysis  of  sensation, 
because  in  this  part  of  the  capsule  are  the  fibers  which  carry 
the  sensory  impulses  from  the  cord  to  the  cortex.  The  cerebral 
ganglia  are  subordinate  centers  :  the  corpus  striatum  with  regard 
to  motion ;  the  optic  thalamus  with  regard  to  sensation,  particu- 
larly to  vision. 

Microscopic  Structure  of  the  Cerebrum  (Figs.  293,  294).— The 


FIG.  293.— The  layers  of  the 
cortical  gray  matter  of  the  cere- 
brum (Meynert). 


llitl 

mmw 


.  d 


FIG.  294. — Schematic  diagram  of  the  cerebral 
cortex:  a,  molecular  layer  with  superficial 
(tangential)  fibers ;  &,  striation  of  Bechtereff- 
Kaes  ;  c,  layer  of  small  pyramidal  cells ;  d, 
stripe  of  Baillarger ;  e,  radial  bundles  of  the 
medullary  substance ;  /,  layer  of  polymor- 
phous cells  (Bohm  and  Davidoff). 


Gray  Matter. — The  gray  matter  on  the  external  surface  of  the  cere- 
brum, the  cortex,  is  divisible  into  five  layers,  whose  distinctness 
varies  in  different  regions,  being  perhaps  most  marked  in  the 
parietal  lobe ;  but  in  the  posterior  portion  of  the  occipital  lobe, 
in  the  gray  portion  of  the  hippocampus  major,  in  the  wall  of 


504 


THE  NERVOUS  SYSTEM. 


the  fissure  of  Sylvius,  and  in  the  olfactory  bulb  this  arrangement 
does  not  exist.     These  layers  are  : 

1.  Molecular  Layer. — This  is  the  most  superficial,  and  consists 
of  neuroglia,  a  few  small  ganglion-cells,  and  a  network  of  non- 
medullated  and  medullated  nerve-fibers,  the  latter  forming  a 
delicate  white  lamina  absent  in  contact  with  the  pia  mater. 


Layer  of 
small  pyr- 
amidal 
cells. 


FIG.  295. — Schematic  diagram  of 
the  cerebral  cortex,  after  Golgi  and 
Eam6n  y  Cajal  (Bohmand  Davidoff). 


FIG,  296.— Large  pyramidal  cell  from 
the  human  cerebral  cortex  ;  chrome-silver 
method  ;  x  150  (Bohm  and  Davidoff). 


The  non-medullated  fibers  have  their  origin  principally  in  the 
small  pyramidal  cells  of  the  second  layer,  but  also  come  from  the 
dendrites  and  axis-cylinder  processes  of  the  cells  of  the  first  layer. 
The  nerve-cells  of  this  layer  have  two  or  three  axis-cylinder 
processes  arranged  horizontally,  which  terminate  by  arborization 
in  this  superficial  layer. 

2.  Smalt  Pyramid-cell  Layer.— The  cells  of  this  layer  are  small 


THE  BRAIN. 


505 


and  pyramidal,  having  a  diameter  of  about  10  //,  with  their 
long  axes  vertical  to  the  surface  of  the  convolutions.  Their 
dendrites  pass  into  the  first  layer;  their  axis-cylinder  processes 
passing  off  from  the  base  give  off  collaterals  and  form  projection- 
fibers  which  go  to  the  corpus  striatum. 

3.  Large  Pyramid-cell  Layer. — This  layer  is  characterized  by 
being  made  up  of  pyramidal  cells  larger  than  those  of  the  second 
layer,  and   increasing  in  size 

from  above  downward,  reach- 
ing a  diameter  of  40  /JL.  The 
breadth  of  this  layer  is  shown 
in  the  illustration.  The  axis- 
cylinder  processes  of  these 
cells  give  off  collaterals  and 
pass  into  the  white  substance 
of  the  brain,  where  they  be- 
come medullated. 

4.  Polymorphous-cell  Layer 
(Fig.  295).— The  cells  of  this 
layer  are  irregular  in  shape, 
each  giving  off  several   den- 
drites   and    an    axis-cylinder 
process.     Some  of  these  proc- 
esses pass  into  the  white  cen- 
ter, while  others  pass  to  the 
first  layer  and  are  contained 
in  one  of  its  fibers. 

5.  Fusiform-cell    Layer. — 
In    this    layer    are    spindle- 
shaped  or  fusiform  cells.     In 


the   inner  half  thev  are    nu- 


FIG.  297. — Principal  types  of  cells  in  the 
cerebral  cortex :  A,  medium-sized  pyrami- 
meroilS   and  arranged    parallel     dal  cell  of  the  second  layer ;  B,  large  pyram- 

to  the  snrfarp      Thp  rlni/tfri/m     idal  cel1  of  third  layer">  ^  polymorphous 
,ce.     ine  ciaustrum    cell  of  fourth  layer;  D  cell  of  wnich  the 

IS  made  Up  OI  this  layer,  sepa-     axis-cylinder  process  is  ascending ;  E,  neu- 

rated  by  white  substance  from    r°glia  c/n ;  ^  cel1  ?f  the  &™*> or  molecular, 

layer,  forming  an  intermediate  cell-station 
between  sensory  fibers  and  motor  cells. 
Notice  the  tangential  direction  of  the  nerve- 


the  other  gray  matter. 

The  different  varieties  of 


-.-,.  fibers ;  G,  sensory  fibers  from  the  white 
cells  are  well  shown  m  Fig.  matter;  H,  white  matter;  J,  collateral  of 
297.  The  number  of  cells  in  *he  white  matter  (Ramon  y  Cajal). 

the  cortex  has  been  estimated 

at  1,200,000,000  by  Donaldson,  and  9,200,000,000  by  Thompson  : 
the  latter  regards  1 59,960  of  these  as  motor ;  this  number  would 
therefore  represent  the  largest  pyramidal  cells  or  "  giant-cells." 

White  Matter. — The  medullated  nerve-fibers  of  the  white 
center  are  traced  through  the  deeper  layers  of  the  gray  matter. 
Some  are  continuous  with  the  axis-cylinder  processes  of  the 
pyramidal  and  polymorphous  cells;  others  arborize  around  the 


506  THE  NERVOUS  SYSTEM. 

cells  of  the  various  layers  without  being  anatomically  in  connection 
with  them.  If  the  axis-cylinder  processes  of  tbe  pyramidal  cells 
are  traced,  it  will  be  found  that  they  take  various  courses.  Some, 
commissural  fibers,  pass  either  directly  or  by  collaterals  through  the 
corpus  callosum  from  one  hemisphere  to  the  other ;  some  join 
association  fibers,  and  pass  into  the  gray  matter  of  other  parts  of 
the  same  hemisphere  as  that  in  which  they  originated ;  while 
others,  projection  fibers — and  this  is  the  course  particularly  of  those 
having  their  origin  in  the  largest  pyramidal  cells — pass  downward 
through  the  corona  radiata,  internal  capsule,  and  pyramidal  tract. 
The  number  of  pyramidal  fibers  has  been  estimated  at  158,222 
by  Blocq  and  Ozanoif. 

The  white  matter  of  the  cerebrum,  consisting  of  medullated 
nerve-fibers,  may  then  be  divided  into  three  groups : 

1.  Those  fibers  that  connect  the  cerebrum  with  the  medulla 
oblongata,  pons  Varolii,  and  spinal  cord.     These  are  the  crura 
cerebri  or  cerebral  peduncles;  hence  the  group  is  described  as 
peduncular  or  projection  fibers.     It  will  be  remembered  that  the 
crura  cerebri  consist  of  the  crusta  and  tegmentum.     The  fibers 
which  come  from  the  pyramids  of  the  medulla  and  are  continued 
through  the  pons  aid  in  forming  the  crusta.     To  these  fibers  are 
added  others  which  originate  in  the  gray  matter  of  the  aqueduct 
of  Sylvius  and  in  the  locus  niger. 

After  forming  the  crura  cerebri  the  fibers  pass  upward  :  some 
of  them  go  directly  to  the  gray  matter  of  the  cortex  :  these  form 
the  corona  radiata ;  others  go  to  the  internal  capsule,  and  thence 
to  the  corpora  striata,  where  they  terminate ;  while  some  of  the 
others  continue  on,  receiving  fibers  from  these  bodies,  and  together 
they  assist  in  forming  the  corona  radiata.  More  fibers  come  from 
the  corpora  striata  than  end  there,  so  that  the  number  of  those 
which  emerge  is  greater  than  the  number  of  those  which  enter. 

The  tegmentum  of  the  crus  is  made  up  of  fibers  from  the 
anterior  and  lateral  columns  of  the  cord,  the  olivary  body,  funiculus 
cuneatus,  funiculus  gracilis,  corpora  quadrigemina,  corpora  genicu- 
lata,  and  the  superior  peduncles  of  the  cerebellum.  These 
fibers  pass  into  the  optic  thalami,  some  terminating  there,  while 
others  pass  through.  To  these  latter  are  added  fibers  having  their 
origin  in  the  optic  thalami,  and  together  they  assist  in  forming 
the  corona  radiata,  being  traced  to  the  cells  in  the  cortical  sub- 
stance of  the  temporosphenoidal  and  occipital  lobes. 

2.  The  second  group  of  fibers  in  the  cerebrum  consists  of  those 
which  connect  the  hemispheres  and  the  basal  ganglia,  and  are  the 
transverse  or  commissural  fibers.     They  compose  the  corpus  callo- 
sum and  the  anterior  and  posterior  commissures.     The  fibers  of 
the  corpus  callosum  connect  the  hemispheres,  being  traced  into 
the  convolutions  and  intersecting  those  of  the  corona  radiata.    The 
anterior  commissure  connects  the  corpora  striata,  and  then  passes 
through  these  bodies  into  the  temporosphenoidal  lobe.     Some  of 


THE  BRAIN. 


507 


the  fibers  of  the  posterior  commissure  connect  the  optic  thalami, 
while  some  come  from  the  tegmentum  of  one  side,  traverse  the 
optic  thalamus,  and  terminate  in  the  white  matter  of  the  temporo- 
sphenoidal  lobe  of  the  other  side. 

3.  The  third  group,  association  fibers,  connect  different  struct- 
ures in  the  same  hemisphere ;  as  the  short  association  fibers,  which 
connect  adjacent  convolutions,  and  the  long  association  fibers,  which 
connect  more  distant  parts. 

Functions  of  the  Cerebrum. — That  the  cerebrum  is  not  essential 
to  life  has  been  demonstrated  experimentally  many  times  in  birds, 
fishes,  rats,  and  other  animals.  Of  course,  the  same  kind  of  proof 
is  not  available  in  man,  but  there  are  instances  on  record  in  which 


FIG.  298. — Dr.  Harlow's  case  of  recovery  after  the  passage  of  an  iron  bar  through 

the  head. 

the  destruction  of  cerebral  tissue  has  been  so  great  as  to  warrant  the 
statement  that  in  man,  as  well  as  in  lower  animals,  life  may  be 
maintained  without  the  influence  of  the  cerebrum.  A  remark- 
able instance  is  that  of  a  man  who  was  injured  by  a  premature 
blast,  an  iron  bar,  one  inch  in  diameter,  being  driven  through  the 
skull  and  brain.  Although  delirious  and  unconscious  for  several 
weeks,  he  finally  recovered,  with  but  the  loss  of  one  eye.  He 
lived  more  than  twenty  years  after  the  injury,  and  performed  the 
work  of  a  coachman  and  a  farm-laborer. 

The  cerebrum  is  undoubtedly  the  seat  of  the  intellectual 
faculties.  A  study  of  the  lower  animals  reveals  the  fact  that 
according  as  the  hemispheres  are  developed  the  signs  of  intelli- 
gence are  increased  :  when  these  structures  are  destroyed  there  is 
an  absence  of  these  manifestations. 

When  the  hemispheres  are  removed,  spontaneous  action  ceases. 
In  studying  the  reflex  action  of  the  spinal  cord  in  a  decapi- 
tated frog  it  was  seen  that  the  animal  made  no  attempt  to  move 


508  THE  NERVOUS  SYSTEM. 

f 

or  change  its  position  unless  some  stimulus  was  applied,  and 
that  as  soon  as  this  stimulus  was  withdrawn  it  lapsed  into  its 
original  position,  remaining  therein  until  again  disturbed.  If  the 
hemispheres  are  removed  from  a  pigeon,  it  will  act  very  much  as 
does  the  frog.  If  disturbed,  it  may  fly  for  a  short  distance,  but  at 
once  lapses  into  a  state  of  apparent  unconsciousness,  with  eyes 
closed.  When  the  foot  is  pinched,  it  will  be  withdrawn.  If  a  pistol 
is  discharged,  the  bird  will  open  its  eyes  and  show  unmistakably 
that  the  report  was  heard,  but  the  discharge  seems  to  produce  no 
other  effect.  The  fact  that  there  is  danger  is  not  appreciated.  It 
seems,  therefore,  that  the  faculty  is  absent  by  which  the  bird  in 
health  associates  danger  with  such  sounds.  When  the  human  brain 
is  diseased  or  injured,  something  of  the  same  kind  is  witnessed,  and 
in  idiots,  whose  brains  are  imperfectly  developed,  the  intellectual 
faculties  are  very  deficient.  Human  intelligence  is  manifested 
through  memory,  reason,  and  judgment. 

Memory  is  the  basis  for  the  action  of  the  other  two  faculties ; 
without  it  there  could  be  neither  reason  nor  judgment.  It  is  the 
faculty  of  the  mind  by  which  it  retains  the  knowledge  of  previous 
thoughts  or  events,  the  actual  and  distinct  retention  and  recogni- 
tion of  past  ideas  in  the  mind.  Afferent  impulses  are  continually 
reaching  the  cells  of  the  cortex  of  the  brain,  and  these  impulses 
produce  impressions  more  or  less  permanent.  If  they  were  evanes- 
cent, passing  away  almost  as  soon  as  received,  memory  would  be 
impossible ;  but  it  is  this  retention  which  constitutes  memory. 
If  the  ideas  produced  by  these  impulses  come  again  into  existence 
spontaneously  and  without  effort,  this  is  remembrance;  if  this 
requires  an  effort,  this  is  recollection,  a  re-collecting  of  the  im- 
pressions originally  produced  on  the  cells  by  afferent  impulses. 

Reason  is  the  faculty  of  the  mind  by  which  is  appreciated  the 
nature  of  nervous  impulses,  and  by  which  they  are  referred  to 
their  external  source — by  which  an  effect  is  referred  to  its  cause. 
This  reference  an  idiot  cannot  make ;  hence  he  is  said  to  be 
"  un-reasonable." 

Judgment  is  the  faculty  of  the  mind  by  which  a  selection  is 
made  of  the  proper  means  to  be  used  in  the  attainment  of  a  par- 
ticular end.  Thus  if  one  selects  inadequate  means  for  the  accom- 
plishment of  a  given  object,  it  is  said  that  one  "  lacks  judgment." 

The  cerebrum  is  the  seat  of  conscious  sensation,  as  opposed  to 
sensation  alone.  The  gray  matter  of  the  spinal  cord  is  said  to  be 
sensitive — that  is,  it  responds  to  stimuli.  If  the  finger  is  burned, 
the  afferent  impulse  is  received  by  the  gray  matter  of  the  cord 
and  a  motor  impulse  passes  out  to  the  muscles.  But  if  the  impulse 
travels  no  farther  than  the  cord,  there  is  no  conscious  sensation. 
To  excite  this  sensation  it  must  proceed  to  the  gray  matter  of  the 
cerebral  cortex.  It  is  in  the  cells  of  the  cortex  that  volitional 
impulses  have  their  origin.  The  gray  matter,  then,  is  the  seat  of 


THE  BRAIN. 


509 


the  will  as  well  as  the  conscious  center,  and  when  largely  diseased 
or  destroyed,  the  only  movements  made  are  involuntary,  depending 
on  other  nerve-centers. 

Cerebral  Localization. — Although  the  study  of  the  intellectual 
faculties  is  both  difficult  and  abstruse,  much  advance  has  in  late 
years  been  made  in  the  knowledge  of  the  physiology  of  the  cere- 
brum, so  far  as  relates  to  the  production  of  voluntary  movements 
and  the  reception  of  sensation.  Observations  upon  both  man  and 
the  lower  animals  have  led  to  the  belief  that  the  power  of  pro- 
ducing certain  movements  is  limited  to  certain  restricted  areas  of 
the  brain,  and  that  other  areas  are  connected  with  sensation. 


Lobulus  paracentralis, 


FIG.  299.— Lateral  view  of  the  brain :  gyri  and  lobuli  marked  with  antique  type, 
the  sulci  and  fissures  with  italic  type  (from  Ecker). 

These  are  known  respectively  as  motor,  sensorimotor,  or  Icinesthetic 
or  Rolandic  areas,  and  sensory  areas.  The  localizing  of  these 
functions  is  cerebral  localization. 

These  observations  had  their  beginning  in  1870.  It  was  found 
that  when  galvanic  currents  were  applied  to  certain  parts  of  the 
cerebral  convolutions  movements  of  particular  muscles  followed, 
and  that  in  order  to  excite  these  muscles  these  parts  or  areas  must 
be  stimulated.  Although  the  dog  was  first  experimented  upon, 
other  animals  (cat,  rabbit,  and  monkey)  have  furnished  like  results. 
In  the  application  of  these  experiments  the  animal  is  put  under 
ether,  the  skull  is  trephined,  and  the  poles  of  a  galvanic  battery 
are  applied  to  the  convolutions.  When  on  such  stimulation  of  a 


510 


THE  NERVOUS  SYSTEM. 


given  spot  or  area  contractions  of  certain  muscles  or  groups  of 
muscles  follow,  and  when  its  extirpation  causes  paralysis  of  these 
muscles,  such  spot  or  area  is  said  to  be  the  motor  area  for  these 
muscles. 

The  following  statement  summarizes  in  a  general  way  what 
is  known  with  reference  to  cerebral  localization  in  the  human 
subject : 

Motor  Areas  (Figs.  300,  301). — It  has  been  noted  that  the 


FIG.  300.—  The  motor  areas  on  the  outer  surface  of  the  brain. 


FIG.  301.— The  motor  areas  on  the  median  surface  of  the  brain. 

Rolandic  area  is  also  called  sensorimotor  and  kinesthetic.  This  is 
because  it  has  been  determined  that  the  sensory  fibers  from  the 
skin  and  also  from  muscles  terminate  in  the  Rolandic  area,  as  well 
as  that  the  motor  fibers  have  their  origin  here. 

The  motor  areas  are  grouped  about  the  fissure  of  Rolando  and 
are  as  follows : 


THE  BRAIN. 


511 


Head,  neck,  and  face:  Lower  two-thirds  of  the  ascending 
frontal  and  the  bases  of  the  lower  and  middle  transverse  frontal 
convolutions. 

Upper  limb :  Upper  third  of  the  ascending  frontal,  base  of 
upper  transverse  frontal,  ascending  parietal,  and  part  of  the  mar- 
ginal convolutions. 

Lower  limb :   Parietal  lobule  and  posterior  part  of  marginal. 

Trunk :    Marginal  convolution  between  the  leg  and  arm. 

It  is  to  be  understood  that  the  action  is  in  all  cases  crossed — 
that  is,  excitation  of  one  side  of  the  cerebrum  causes  the  move- 
ments spoken  of  to  occur  on  the  opposite  side  of  the  body,  and 
the  same  is  true  of  the  paralysis  which  follows  disease  or  injury. 

As  a  result  of  destruction  of  the  Rolandic  area  degeneration 


'Filltt 


F 


MID  BRAIN 


FIG.  302. — Degeneration  after  destruction  of  the  Eolandic  area  of  the  right  hemi- 
sphere (after  Gowers). 

occurs,  and  its  course  is  well  shown  in  the  illustration  (Fig.  302), 
in  which  the  shaded  portions  represent  the  parts  that  have  under- 
gone degeneration. 

Speech-center. — Articulate  speech  requires  the  exercise  of 
memory  and  the  power  of  producing  certain  voluntary  move- 
ments. Inability  to  produce  articulate  speech  is  known  as  aphasia. 
If  the  memory  of  words  is  absent  while  the  power  to  produce 
the  movements  remains,  it  is  amnesic  aphasia,  and  if  the  reverse 
condition  exists,  it  is  ataxic  aphasia.  It  is  believed  that  the 
center  which  presides  over  language  is  in  the  frontal  lobe  on 
the  left  side,  and  has  received  from  its  discoverer  the  name  of 
Broca's  convolution.  Some  localize  it  in  the  third  frontal  convo- 
lution ;  others  regard  it  as  being  more  diffused,  and  locate  the 
center  in  the  convolutions  surrounding  the  lower  end  of  the  fissure 


512 


THE  NERVOUS  SYSTEM. 


of  Sylvius.     It  is  on  the  left   side  in   persons   that  are  right- 
handed,  and  on  the  right  side  in  those  that  are  left-handed. 

Sensory  Areas. — When  a  sensory  area  is  stimulated.,  the  move- 
ment which  results  is  reflex.  Thus,  if  the  auditory  area,  which 
was  localized,  perhaps  incorrectly,  by  Ferrier  in  the  superior 
temporosphenoidal  convolution,  is  stimulated,  the  animal  pricks 
up  its  ears  and  turns  its  head  to  the  opposite  side.  If  a  sensory 


FIG.  303.— Base  of  brain :  1,  2,  3,  cerebrum  ;  4  and  5,  longitudinal  fissure ;  6, 
fissure  of  Sylvius ;  7,  anterior  perforated  spaces ;  8,  infundibulum ;  9,  corpora  albi- 
cautia ;  10,  posterior  perforated  space  ;  11,  crura  cerebri ;  12,  pons  Varolii ;  13,  junc- 
tion of  spinal  cord  and  medulla  oblongata ;  14,  anterior  pyramid ;  14X,  decussation 
of  anterior  pyramid ;  15,  olivary  body  ;  16,  restiform  body  ;  17, ,  cerebellum ;  19, 
crura  cerebelli ;  21,  olfactory  sulcus;  22,  olfactory  tract;  23,  olfactory  bulbs;  24, 
optic  commissure;  25,  motor  oculi  nerve:  26,  patheticus  nerve;  27,  trigeminus 
nerve  ;  28,  abducens  nerve ;  29,  facial  nerve ;  30,  auditory  nerve ;  31,  glossopbaryn- 
geal  nerve ;  32,  pneumogastric  nerve ;  33,  spinal  accessory  nerve ;  34,  hypoglossal 
nerve. 

area  is  extirpated,  there  is  a  loss  of  the  sense  presided  over  by 
this  area. 

Visual  Area. — This  is  located  in  the  occipital  lobe  and  the 
angular  gyrus. 

Auditory  Area. — Ferrier  located  this  in  the  superior  temporo- 
sphenoidal convolution. 

The  location  of  other  areas  is  a  matter  of  considerable  doubt. 


THE  BRAIN.  513 

Cranial  Nerves  (Fig.  303). — The  cranial  nerves  have  their 
origin  in  the  gray  matter  at  the  base  of  the  brain,  and  they  escape 
from  the  skull  by  various  openings,  or  foramina,  to  reach  the  parts 
to  which  they  are  distributed.  The  only  exception  to  this  is  the 
spinal  accessory,  a  part  of  which  arises  from  the  gray  matter  of 
the  cord.  Among  the  cranial  nerves  are  those  of  special  sense, 
of  motion,  and  nerves  having  both  motor  and  sensory  properties. 
The  points  at  which  they  leave  the  brain  are  spoken  of  as  their 
apparent  origin,  but  this  is  only  apparent,  for  they  can  be  traced 
into  the  brain-substance,  to  collections  of  nerve-cells,  nerve- 
centers,  to  which  the  name  nuclei  has  been  given.  The  nucleus 
of  a  nerve  is  its  real  origin. 

Of  cranial  nerves  there  are  12  pairs,  the  number  of  each  indicat- 
ing the  order,  from  before  backward,  in  which  it  escapes  from  the 
cavity  of  the  cranium:  1.  Olfactory;  2.  Optic;  3.  Motor  oculi 
communis ;  4.  Patheticus  or  trochlearis ;  5.  Trigeminus ;  6.  Ab- 
dticens  ;  7.  Facial ;  8.  Auditory  ;  9.  Glossopharyngeal ;  10.  Pneu- 
mogastric;  11.  Spinal  accessory;  12.  Hypoglossal. 

The  first  two  nerves,  the  olfactory  and  the  optic,  will  be 
considered  in  connection  with  the  senses  of  smell  and  sight. 

Motor  Oculi. — The  third  nerve,  motor  oculi,  motor  oculi  com- 
munis, or  oculomotorius,  leaves  the  surface  of  the  brain  at  the  inner 
surface  of  the  crus  cerebri,  just  in  front  of  the  pons  Varolii.  Its  real 
origin  is,  however,  a  nucleus  in  the  floor  of  the  aqueduct  of  Sylvius. 
It  escapes  from  the  cranium  through  the  sphenoidal  fissure,  and  is 
distributed  to  the  superior,  internal,  and  inferior  recti  and  to  the 
inferior  oblique.  It  also  supplies  the  levator  palpebrae  superioris, 
and  sends  a  branch  to  the  ophthalmic,  lenticular,  or  .ciliary  gang- 
lion. Another  way  to  describe  its  distribution  is  to  say  that  it 
supplies  the  levator  palpebrae  and  all  the  muscles  that  move  the 
eyeball,  except  the  superior  oblique  and  external  rectus. 

The  action  of  these  muscles  is  largely  indicated  by  their  names. 
The  levator  palpebrae  by  its  contraction  raises  the  upper  eyelid. 
The  internal  rectus  turns  the  eyeball  inward  toward  the  nose,  and 
the  external  rectus  turns  it  outward.  The  direction  of  action  and  the 
point  of  attachment  of  the  superior  rectus  are  such  that  when  it  con- 
tracts the  eyeball  is  not  only  turned  upward,  but  it  is  also  rotated 
slightly  inward ;  this  is  corrected  by  the  action  of  the  inferior 
oblique,  so  that  the  two  acting  together  produce  a  movement 
directly  upward.  The  same  deviation  inward  follows  when  the 
eye  is  turned  downward  by  the  inferior  rectus,  and  a  similar  cor- 
rection is  made  by  the  action  of  the  superior  oblique.  If  the 
external  and  superior  recti  act  together,  the  movement  of  the 
eyeball  is  in  the  direction  of  the  diagonal — that  is,  outward  and 
upward ;  the  conjoint  action  of  the  external  and  inferior  recti 
causes  the  eyeball  to  move  outward  and  downward,  and  a  corre- 
sponding action  results  when  the  other  adjacent  recti  are  brought 

33 


514  THE  NERVOUS  SYSTEM. 

into  play.  If  the  recti  act  alternately,  the  eyeball  will  be  rotated 
completely,  as  in  looking  around  a  room  from  one  side  to  the 
other  and  back  again,  from  the  floor  to  the  ceiling.  The  motor 
oculi  is  purely  a  motor  nerve.  When  stimulated,  contraction  is 
produced  in  the  muscles  to  which  it  is  distributed ;  when  the 
nerve  is  divided,  these  muscles  are  paralyzed. 

Paralysis  of  the  Motor  Oculi. — When  the  motor  oculi  is  par- 
alyzed, the  following  are  the  results  : 

(a)  External  strabismus,  which  consists  in  a  turning  of  the  eye 
outward.  The  retention  of  the  eye  in  its  normal  position  requires 
the  conjoint  action  of  the  internal  and  external  recti.  In  paralysis 
of  the  motor  oculi  the  internal  rectus  has  lost  its  innervation, 
and  therefore  its  power  to  contract,  and  the  external  rectus, 
which  receives  its  nervous  supply  from  another  nerve  (the  ab- 
ducens),  having  lost  its  antagonist,  turns  the  eye  outward. 

(6)  Luscitas. — After  external  strabismus  has'been  produced  the 
eye  remains  in  that  condition,  for  the  muscles  which  could  move 
it  in  any  other  direction  have  been  paralyzed.  This  immobility 
is  called  "  luscitas." 

(c)  Ptosis. — The  levator  palpebrse  superioris  is  also  paralyzed, 
and  the  upper  eyelid  droops,  constituting  ptosis.      The  ability  to 
close  the  eye  still  remains,  as  this  is  the  act  of  the  orbicularis 
palpebrarum,  which  is  not  innervated  by  the  third,  but  by  the 
seventh,  nerve. 

(d)  Mydriasis. — A  branch  of  the  motor  oculi  goes  to  the  ciliary 
ganglion,  which  gives  off  the  ciliary  nerves  that  supply  the  iris. 
Accompanying  the  manifestations  of  paralysis  of  the  motor  oculi 
already  mentioned  there  is  in  addition  a  dilatation  of  the  pupil,  or 
mydriasis.     The  diminution  of  the  size  of  the  pupil  following  the 
action  of  light  upon  the  retina  does  not  take  place  when  this  nerve 
is  paralyzed.    The  contraction  of  the  pupil  is  a  reflex  act  requiring 
the  integrity  of  the  optic  nerve,  which  serves  as  a  carrier  of  the 
luminous  impressions  to  the  brain,  and  of  the  motor  oculi,  which 
is  the  efferent  nerve  in  this  act. 

(e)  Inability  to  Focus. — The  muscle  concerned  in  focusing  the 
eye  for  short  distances  is  the  ciliary.      The  power  to  focus  is  lost 
in  paralysis  of  the  motor  oculi.     Paralysis  of  the  motor  oculi  may 
be  due  to  disease  of  the  brain  or  to  pressure  on  the  nerve.     If 
the  trunk  of  the  nerve  is  affected,  all  the  physical  signs  mentioned 
may  be  observed,  while  if  a  single  branch  only  is  involved,  the 
effect  will  be  limited  to  the  part  to  which  that  branch  is  dis- 
tributed. 

Trochlearis. — The  apparent  origin  of  the  trochlearis  or  patheti- 
cus  is  on  the  outer  side  of  the  crus  cerebri,  in  front  of  the  pons, 
and  its  real  origin  is  a  nucleus  continuous  with  that  of  the  motor 
oculi.  The  trochlearis  leaves  the  cranium  by  the  sphenoidal 
fissure,  and  is  distributed  to  but  one  muscle,  the  superior  oblique. 


THE  BRAIN.  515 

When  this  nerve  is  paralyzed  the  patient  cannot  turn  the  eye  out- 
ward and  downward ;  the  action  of  the  superior  oblique  is,  there- 
fore, to  turn  the  eye  outward  and  downward.  If  the  head  is  not 
turned  toward  either  side  when  this  nerve  is  paralyzed,  the  only 
thing  observable  is  that  the  patient  sees  double  when  he  looks 
downward,  and  the  image  perceived  by  the  affected  eye  is  oblique 
and  below  that  seen  by  the  eye  that  is  affected.  For  a  further 
discussion  of  the  ocular  muscles  see  p.  556. 

Trigeminus. — This  nerve,  which  is  also  called  "  trifacial,"  has 
received  its  names  from  the  fact  that  it  has  three  subdivisions, 
and  its  latter  name  from  the  fact  that  is  distributed  in  the  main  to 


FIG.  304. — General  plan  of  the  branches  of  the  fifth  pair :  1,  lesser  root  of  the 
fifth  pair :  2,  greater  root,  passing  forward  into  the  Gasserian  ganglion ;  3,  placed 
on  the  bone  above  the  ophthalmic  division,  which  is  seen  dividing  into  the  supra- 
orbital,  lacrimal,  and  nasal  branches,  the  latter  connected  with  the  ophthalmic 
ganglion  ;  4,  placed  on  the  bone  close  to  the  foramen  rotundum,  marks  the  superior 
maxillary  division  ;  5,  placed  on  the  bone  over  the  foramen  ovale,  marks  the  inferior 
maxillary  division  (after  a  sketch  by  Charles  Bell). 

the  parts  about  the  face.  It  arises  by  two  roots,  anterior  and 
posterior.  The  anterior  root,  the  smaller,  is  purely  motor;  the 
posterior  root,  the  larger,  is  sensory,  and  is  characterized  anatomi- 
cally by  having  upon  it  the  Gasserian  ganglion.  The  nerve  leaves 
the  brain  at  the  side  of  the  pons  Varolii.  The  real  origin  of 
the  motor  root  is  a  nucleus  in  the  floor  of  the  fourth  ventricle ; 
the  sensory  root  arises  from  a  nucleus  on  a  level  with  the  middle 
of  the  superior  peduncle  of  the  cerebellum,  just  internal  to  the 
margin  of  the  fourth  ventricle.  Some  authorities  give  it  a  more 
extensive  origin,  from  the  pons  through  the  medulla  and  as  far  as 
the  posterior  cornua  of  the  gray  matter  of  the  spinal  cord. 


516  THE  NERVOUS  SYSTEM. 

The  motor  root  passes  beneath  the  Gasserian  ganglion,  and 
takes  no  part  in  its  formation. 

Beyond  the  ganglion  the  fifth  nerve  divides  into  three  parts : 
(1)  ophthalmic;  (2)  superior  maxillary;  and  (3)  inferior  maxil- 
lary. 

*(1)  Ophthalmic  Division. — This  division,  which  leaves  the 
cranium  by  the  sphenoidal  fissure,  is  distributed  to  the  tentorium 
cerebelli,  the  eyeball,  the  Schneiderian  membrane,  the  lacrimal 
gland,  and  the  skin  about  the  forehead  and  nose  ;  and  also  supplies 
branches  to  the  ciliary  ganglion.  It  contains  fibers  from  the 
posterior  root  only ;  none  from  the  anterior. 

(2)  Superior  Maxillary   Division. — This  division  of  the   fifth 
pair  leaves  the  cranial  cavity  by  the  foramen  rotundum.     It  is 
distributed    to    the    dura    mater,    the    sphenopalatine    ganglion 
(Meckel's),  the   skin   of  the   temple   and    cheek,   the   teeth,  the 
gums,  the  mucous  membrane  of  the  upper  jaw  and  upper  lip,  the 
mucous  membrane  of  the  lower  part  of  the  nasal  passages,  and 
the  skin  of  the  lower  eyelid,  side  of  nose,  and  upper  lip.     There 
are  no  fibers  of  the  anterior  root  in  this  division. 

(3)  Inferior  Maxillary  Division. — As  has  already  been  stated, 
there  is  no  anatomic  connection  between  the  motor  root  of  the 
fifth  nerve  and  the  Gasserian  ganglion.     From  this  ganglion  are 
given  off  nerve-fibers  which  join  the  motor  root,  together  making 
the  inferior  maxillary  division,  which  escapes  through  the  foramen 
ovale.     It  is  distributed  to  the  dura  mater,  the  otic  ganglion,  the 
mucous  membrane  of  the  cheek  and  skin,  the  mucous  membrane 
of  the  lower  lip,  the  anterior  wall  of  the  external  auditory  meatus, 
the  front  of  the  external  ear  and  the  skin  of  the  adjacent  temporal 
region,  the  submaxillary  gland  and  ganglion,  the  mucous  mem- 
brane of  the  mouth  and  tongue ;  to  the  papillae  at   the  tip,  the 
edges,  and  anterior  two-thirds  of  the  tongue,  and  to  the  teeth  and 
gums  of  the  lower  jaw.     It  also  supplies  the  following  muscles : 
Temporal,  masseter,  pterygoid,  mylohyoid,  and  anterior  belly  of  the 
digastric. 

Physiologic  Properties  of  the  Trigeminus. — The  trigeminus  is 
the  largest  of  the  cranial  nerves,  and  its  functions  are  many  and 
important.  It  supplies  the  parts  to  which  it  is  distributed  with 
the  general  sensibility  they  possess.  If  it  is  divided,  there  is 
complete  absence  of  sensation  (anesthesia)  of  the  face  on  the  cor- 
responding side.  So  pronounced  is  this  anesthesia  that  no  amount 
of  irritation  applied  to  such  ordinarily  sensitive  parts  as  the  cornea 
will  produce  any  effect.  An  animal  thus  experimented  upon 
seems  entirely  unconscious  of  the  irritation.  Experimenters  have 
gone  so  far  as  to  exsect  the  eyeball  and  apply  hot  irons  to  the 
skin  without  causing  pain  to  the  animal  experimented  upon. 

Neuralgia  of  the  face,  headache,  and  toothache  are  all  due  to 
some  interference  with  the  normal  functions  of  this  nerve.  It  is 


THE  BRAIN. 


517 


not  an  uncommon  thing  to  hear  patients  complain  of  headaches 
which  seem  to  them  to  be  in  the  brain  itself.  These  deep-seated 
headaches  may  be  due  to  affections  of  one  or  more  of  the  recurrent 
branches  which  come  off  from  the  divisions  of  the  nerve,  and 
which  are  distributed  to  the  dura  mater  and  bones  of  the  skull. 
Lingual  (Gustatory)  Nerve. — This  nerve  is  sometimes  called 
the  "  lingual  branch  of  the  fifth  nerve."  It  is  the  branch  which 
is  distributed  to  the  mucous  membrane  of  the  mouth  and  the  gums, 
and  to  the  mucous  membrane  and  papillae  of  the  tongue.  It  sup- 
plies the  tongue  with  tactile  sensibility,  a  quality  of  great  advan- 
tage in  enabling  one  to  detect  the  physical  properties  of  food,  to 


FIGS.  305,  306. — Distribution  of  the  cutaneous  sensitive  nerves  upon  the  head : 
owa,  orni,  the  occiput,  ma j.  and  minor  (from  the  N.  cervical  II.  and  III.)  ;  am,  N. 
auricular  magn.  (from  X.  cervic.  III.)  ;  cs,  N.  cervical  superfic.  (from  N.  cervic.  III.)  ; 
Fi,  first  branch  of  the  fifth  (so,  N.  supraorbit. ;  st.  N.  supratrochl. ;  it,  N.  infra- 
trochl.  ;  e,  N.  ethmoid. ;  I,  N.  lacrimal.)  ;  Vi,  second  branch  of  the  fifth  (sm,  N. 
subcutan.  malfe  sen  zygomaticus) ;  Fs,  third  branch  of  fifth  (at,  N.  auriculotempor. ; 
b,  N.  buccinator ;  m,  N.  mental.) ;  B,  posterior  branches  of  the  cervical  nerve. 

recognize  in  it  the  presence  of  hard  objects  which  it  would  be 
injurious  to  swallow,  and  to  determine  when  it  is  ready  for 
deglutition.  Besides  this  tactile  sensibility  the  lingual  nerve, 
according  to  some  authorities,  suppli'es  the  anterior  two-thirds  of 
the  tongue  with  the  sense  of  taste,  a  special  sense,  and  this  power 
is  lost  when  the  fifth  pair  or  the  lingual  branch  is  divided.  For 
a  further  consideration  of  this  nerve  see  p.  535. 

Mastication. — The  muscles  that  have  been  mentioned  as  receiv- 
ing branches  of  the  inferior  maxillary  division  are  those  concerned 
in  the  act  of  mastication.  In  this  act  the  temporal  and  masseter 
close  the  mouth,  the  mylohyoid  and  digastric  open  it,  while  the 
pterygoids  produce  the  lateral  movement  of  the  lower  jaw. 
Division  of  the  inferior  maxillary  division  paralyzes,  therefore,  all 


518  THE  NERVOUS  SYSTEM. 

these  muscles.  If  it  is  divided  on  one  side,  the  muscles  on  the 
other  side  can  still  perform  the  act,  but  in  an  imperfect  manner ; 
if  divided  on  both  sides,  all  masticatory  movements  will  be 
abolished. 

Anastomosis  of  the  Fifth  Pair. — Besides  the  branches  already 
mentioned,  there  are  others  which  are  termed  anastomotic  branches. 
Although  the  upper,  middle,  and  lower  parts  of  the  face  are  sup- 
plied with  sensation  by  the  ophthalmic,  superior  maxillary,  and 
inferior  maxillary  divisions  respectively,  still  the  boundaries  of 
each  are  not  absolute.  Thus  the  skin  of  the  nose  is  supplied  by 
fibers  from  the  ophthalmic  and  superior  maxillary,  and  the  skin 
of  the  temporal  region  is  supplied  from  both  the  superior  and 
inferior  maxillary  divisions.  In  addition  to  these  branches,  there 
are  some  which  unite  with  other  nerves  and  give  a  certain  amount 
of  sensibility  to  the  parts  to  which  these  nerves  are  distributed. 
A  striking  instance  of  this  is  the  branch  which  anastomoses  with 
the  facial  nerve.  This  nerve  is  at  its  origin  purely  motor,  and  is 
distributed  to  the  muscles  of  the  face.  These  muscles  are  endowed 
with  sensibility ;  but  this  is  not  due  to  fibers  of  the  facial  nerve, 
but  to  those  of  the  fifth  nerve,  which  anastomose  with  the  facial 
and  go  with  it  to  its  termination  in  the  muscles. 

Connection  of  the  Fifth  Pair  with  the  Special  Senses. — After 
division  of  the  fifth  nerve  the  special  senses  of  smell,  sight,  taste, 
and  hearing  are  seriously  affected.  The  Schneiderian  membrane 
becomes  swollen,  and  later  assumes  a  fungous  condition  and  bleeds 
readily  when  touched.  There  is  besides  an  accumulation  of  altered 
mucus  in  the  nasal  passages.  The  eye  also  undergoes  marked 
changes :  The  conjunctiva  becomes  congested  and  the  cornea 
opaque  ;  later,  most  of  the  structures  of  the  eye  suffer  from  inflam- 
matory changes  to  the  degree  of  destruction.  The  sense  of  taste 
may  likewise  be  lost,  not  only  in  the  anterior  two-thirds  of  the 
tongue,  but  also  in  the  posterior  third  as  well.  Besides,  the  sense 
of  hearing  may  also  be  greatly  impaired. 

The  explanation  of  these  changes  is  not  an  easy  one.  Some 
authorities  regard  them  as  due  to  disturbance  of  trophic  in- 
fluences. The  nerve-fibers  which  form  the  posterior  or  sensory 
root  of  the  fifth  pair  in  passing  through  the  Gasserian  ganglion 
are  reinforced  by  fibers  which  have  their  origin  in  this  collection 
of  nerve-cells.  Each  of  the  three  divisions  of  the  trigeminus 
contains,  therefore,  fibers  of  the  posterior  root,  and  in  addition 
fibers  from  the  ganglion.  The  latter  fibers  are  distributed  to  the 
structures  to  which  the  accessory  fibers  are  distributed,  and  they 
are  regarded  as  trophic  nerves — that  is,  as  nerves  which  regulate 
the  nutrition  of  the  parts  to  which  they  go.  Among  these  parts 
are  the  mucous  membrane  of  the  nose,  the  cornea,  the  conjunctiva, 
and  the  tongue,  and  the  loss  of  the  special  senses  is  believed  to  be 
due  to  altered  nutrition  of  the  affected  parts.  The  sense  of  sight 


THE  BRAIN.  519 

is  resident  in  the  retina  and  optic  nerve,  but  it  may  be  as  perfectly 
abolished  by  rendering  opaque  the  tissues  through  which  light 
reaches  these  structures  as  by  dividing  the  optic  nerve.  Thus 
in  cases  where  a  tumor  presses  upon  the  trigeminus  in  front  of 
the  ganglion,  not  only  may  there  be  an  alteration  of  the  nutrition 
of  the  skin  of  the  face,  as  evidenced  by  an  herpetic  eruption, 
but  there  may  be  also  the  corneal  ulceration  already  referred  to. 
In  like  manner  the  olfactory  nerves  are  the  nerves  of  smell,  but 
if  the  nasal  mucous  membrane  is  so  aifected  in  its  nutrition  as  to 
render  the  function  of  the  nerves  impossible,  the  sense  of  smell 
is  as  certainly  abolished  as  if  the  olfactory  bulb  was  broken  up. 
This  interference  with  the  normal  action  of  the  nerves  is  seen  in 
catarrhs!  affections  of  the  nose,  in  which  the  sense  of  smell  is 
much  obtunded  and  sometimes  even  lost. 

Some  authorities,  however,  question  the  existence  of  specific 
trophic  nerves.  Stewart  says  that  up  to  the  present  "  no  unequivo- 
cal proof,  experimental  or  clinical,  has  ever  been  given  of  the  existence 
of  specific  trophic  nerves."  These  authorities  consider  that  the 
inflammatory  changes  occurring  in  the  eye,  for  instance,  are  due  to 
the  presence  of  foreign  bodies  lodging  on  the  eyeball,  which  has 
lost  its  sensibility ;  that  if  the  eye  is  so  protected  that  irritating 
substances  cannot  injure  it,  the  degenerative  changes  take  place 
only  after  a  considerable  time ;  and  that  when  they  do  occur  it  is 
probably  even  then  due  to  injury,  for  it  is  a  most  difficult  thing  to 
protect  the  eye  for  a  long  time  from  all  sources  of  irritation. 
Thus  in  a  case  reported  by  ShawT,  in  which  both  the  fifth  and  the 
third  nerves  were  paralyzed,  due  to  the  pressure  of  a  tumor  at  the 
base  of  the  brain,  no  change  took  place  in  the  nutrition  of  the 
eye.  The  orbicularis  could  still  close  the  eye,  and  the  protection 
which  this  gave  was  augmented  by  the  ptosis.  After  many  months 
the  growth  of  the  tumor  involved  the  facial  nerve,  and  as  the  eye 
could  then  not  be  closed,  inflammatory  changes  soon  set  in  and 
sight  was  destroyed. 

Gowers  also  reports  a  case  in  which  the  patient  lived  for  seven 
years  with  complete  paralysis  of  the  fifth  nerve,  yet  the  eye  re- 
mained free  from  disease  and  the  sight  was  unimpaired. 

Kirkes,  on  the  other  hand,  is  an  advocate  of  the  existence  of 
the  "  trophic  influence  of  nerves/'  although  he  states  that  the 
proof  that  there  are  distinct  trophic  nerve-fibers  anatomically  is 
not  very  conclusive.  He  thinks  that  the  division  or  disease  of  the 
fifth  nerve,  for  instance,  acts  as  a  predisposing  cause,  and  the  dust 
which  falls  on  the  cornea  as  the  exciting  cause.  He  gives  one 
instance  of  disturbance  of  nutrition  which  it  is  difficult  to  account 
for  except  on  the  theory  of  trophic  nerves.  He  says  :  "  Many 
bed-sores  are  due  to  prolonged  confinement  in  bed  with  bad 
nursing ;  these  are  of  slow  onset.  But  there  is  one  class  of  bed- 
sores which  are  acute  :  these  are  especially  met  with  in  cases  of 


520  THE  NERVOUS  SYSTEM. 

paralysis  due  to  disease  of  the  spinal  cord ;  they  come  on  in  three 
or  four  days  after  the  onset  of  the  paralysis  in  spite  of  the  most 
careful  attention  ;  they  cannot  be  explained  by  vasomotor  dis- 
turbance nor  by  loss  of  sensation ;  there  is,  in  fact,  no  doubt  they 
are  of  trophic  origin ;  the  nutrition  of  the  skin  is  so  greatly  im- 
paired that  the  mere  contact  of  it  with  the  bed  for  a  few  days  is 
sufficient  to  act  as'  the  exciting  cause  of  the  sore." 

The  subject  is  one  of  great  importance,  but  must  be  regarded 
as  still  unsettled. 

Ganglia  of  the  Trigeminus. — Besides  the  Gasserian  ganglion, 
there  are,  in  connection  with  the  fifth  nerve,  four  ganglia  which 
are  by  some  writers  described  as  a  part  of  the  sympathetic  system. 
They  are  the  ciliary  or  ophthalmic,  the  sphenopalatine  or  MeckePs, 
the  otic  or  Arnold's,  and  the  submaxillary. 

The  ciliary  ganglion  belongs,  according  to  some  authorities,  to 
the  third  rather  than  to  the  fifth  nerve.  It  is  not  larger  than  the 
head  of  an  ordinary  pin,  and  is  situated  in  the  orbit.  The 
branches  by  which  other  nerves  communicate  with  it  are  called  its 
"  roots  "  ;  of  these  there  are  three  :  The  sensory,  from  the  ophthal- 
mic division  of  the  fifth ;  the  motor,  from  the  motor  oculi ;  and 
the  sympathetic,  from  the  cavernous  plexus  of  the  sympathetic. 
The  nerves  that  go  off  from  it  are  the  short  ciliary  nerves,  which, 
joining  with  the  long  ciliary  nerves,  form  the  nasal  branch  of  the 
ophthalmic  division,  and  together  they  are  distributed  to  the  ciliary 
muscle,  the  iris,  and  the  cornea.  These  nerves  supply  motion 
to  the  sphincter  and  dilator  pupillse,  sensibility  to  the  iris,  choroid, 
and  sclerotic,  and  vasomotor  influences  to  the  blood-vessels  of 
the  iris,  choroid,  and  retina.  If  the  trophic  influerfce  already 
spoken  of  exists,  it  must  be  conveyed  to  the  eye  through  the 
ciliary  nerves. 

The  sphenopalatine  or  Meckel's  ganglion,  which  is  the  largest 
of  the  four,  is  situated  in  the  sphenomaxillary  fossa.  This  gang- 
lion also  has  three  roots  :  The  sensory,  sphenopalatine,  from  the 
superior  maxillary  division  of  the  fifth  ;  the  motor,  large  superficial 
petrosal  nerve  from  the  facial ;  and  the  sympathetic,  large  deep 
petrosal  nerve  from  the  carotid  plexus  of  the  sympathetic.  The 
Vidian  nerve  is  made  by  the  union  of  these  two  latter  nerves. 
The  nerves  from  this  ganglion  are  distributed  to  the  posterior  por- 
tion of  the  nasal  passages  and  the  hard  and  soft  palate,  giving 
them  sensibility  ;  to  the  levator  palati  and  azygos  uvulae,  giving 
them  the  power  of  motion ;  and  to  the  blood-vessels  of  this 
region. 

The  otic  or  Arnold's  ganglion  is  situated  on  the  inner  side  of  the 
inferior  maxillary  division  of  the  fifth,  just  below  the  foramen 
ovale.  It  likewise  has  three  roots  :  The  sensory,  from  the  inferior 
maxillary  and  glossopharyngeal ;  the  motor,  from  the  facial  and 
inferior  maxillary ;  and  the  sympathetic,  from  the  plexus  around 


THE  BRAIN.  521 

the  meningeal  artery.  Its  branches  of  distribution  are  to  the 
tensor  tympani,  the  tensor  palati,  and  a  small  one  to  the  chorda 
tympani.  The  mucous  membrane  of  the  tympanum  and  the 
Eustachian  tube  is  also  supplied  by  this  ganglion. 

The  submaxillary  ganglion,  which  is  situated  near  the  sub- 
maxillary  gland,  receives  branches  of  communication  from  the 
lingual  branch  of  the  fifth,  chorda  tympani,  and  sympathetic 
plexus  around  the  facial  artery.  Its  branches  of  distribution  are 
to  the  mucous  membrane  of  the  mouth  and  Wharton's  duct,  also 
to  the  submaxillary  gland. 

Abducens. — This  nerve,  which  has  its  real  origin  in  the  floor 
of  the  fourth  ventricle,  emerges  from  the  cranium  by  the  sphe- 
noidal  fissure,  and  is  distributed  to  the  external  rectus  muscle.  It 
is  a  motor  nerve,  as  is  shown  by  the  contraction  of  this  muscle 
when  the  nerve  is  stimulated,  and  by  its  paralysis  when  the  nerve 
is  divided. 

Paralysis  of  Abducens. — When  from  any  cause  this  nerve  is 
so  injured  as  to  deprive  it  of  its  function,  the  internal  rectus,  having 
lost  its  antagonist,  the  external  rectus,  turns  the  eye  inward  toward 
the  nose,  producing  internal  strabismus.  There  may  also  be  some 
contraction  of  the  pupil,  because  the  radiating  fibers  of  the  iris, 
which  cause  dilatation  of  the  pupil,  are  to  a  certain  extent  deprived 
of  their  innervation,  this  being  supplied  from  the  sympathetic, 
some  of  the  nerves  of  which  system  run  along  with  the  abducens, 
and  when  this  nerve  is  injured,  these  sympathetic  fibers  may  also 
be  involved.  It  is  said  that  the  abducens  is  more  frequently  im- 
plicated in  fractures  at  the  base  of  the  skull  than  any  other  cranial 
nerve. 

Facial  Nerve. — The  facial  nerve  leaves  the  medulla  oblongata 
at  the  groove  between  the  olivary  and  the  restiform  bodies.  Its 
real  origin  is  a  nucleus  in  the  floor  of  the  fourth  ventricle.  It 
leaves  the  cranium  by  the  internal  auditory  meatus,  through  which 
and  the  aqueduct  of  Fallopius  it  passes  to  emerge  at  the  stylo- 
mastoid  foramen.  In  the  older  nomenclature,  in  which  there  were 
but  nine  pairs  of  nerves,  the  facial  was  associated  under  the  name 
of  seventh  nerve  with  the  auditory  nerve,  in  company  with  which 
it  enters  the  auditory  meatus ;  the  facial,  from  its  firm  consistency, 
being  called  the  portio  dura,  and  the  auditory,  on  account  of  its 
opposite  quality,  being  called  the  portio  mollis. 

The  facial  has  a  very  extensive  distribution — the  muscles  of 
the  face  and  external  ear,  the  stylohyoid,  posterior  belly  of  the 
digastric,  the  platysma  myoides,  and  the  stapedius.  It  also  gives 
off  the  chorda  tympani,  which  is  distributed  to  the  submaxillary 
gland  and  ganglion,  to  the  inferior  lingualis  muscle,  and  to  the 
sublingual  gland.  Besides  these  it  has  most  important  branches 
of  communication  with  the  sympathetic  system  and  with  the 
glossopharyngeal,  pneumogastric,  and  trigeminus  nerves. 


522  THE  NERVOUS  SYSTEM. 

Physiologic  Properties  of  the  Facial. — The  facial  is,  origi- 
nally, a  purely  motor  nerve,  and  whatever  sensibility  is  possessed 
by  the  parts  to  which  it  is  distributed  is  not  due  to  facial  fibers, 
but  to  anastomotic  fibers  from  other  nerves,  principally  the  fifth. 
The  most  pronounced  function  of  the  facial  is  its  relation  to  ex- 
pression. The  so-called  "  expression  "  of  the  face  is  caused  by 
different  degrees  of  contraction  of  the  facial  muscles,  and  the 
different  expressions,  such  as  of  fear,  of  anger,  etc.,  are  due  to  con- 
traction of  different  muscles.  The  facial  is  therefore  said  to  be 
the  "  nerve  of  expression,"  and  when  it  is  divided  and  the  muscles 
paralyzed,  the  reason  for  this  title  is  readily  understood. 

Facial  Paralysis. — When  the  facial  nerve  is  divided  or  its 
functions  otherwise  abolished,  the  following  are  the  results : 

(1)  Effect  of  Facial  Paralysis  on  Facial  Expression. — A  com- 
plete loss  of  expression  follows  on  the  affected  side ;  the  wrinkles 
on  that  side  are  obliterated  and  the  face  is  flattened. 

(2)  Effect  of  Facial  Paralysis  on  the  Eye. — The  muscle  which 
closes  the  eye  is  the  orbicularis  palpebrarum  ;  this  muscle  is  inner- 
vated by  the  facial  nerve,  and  in  paralysis,  therefore,  the  eye 
remains  permanently  open,  the  power  to  close  it  being  lost.     Inas- 
much as  the  act  of  winking  is  but  a  rapid  partial  closing  of  the  eye, 
this  act  is  also  abolished  and  the  eyeball  is  liable  to  become  dry. 
The  act  of  winking  spreads  the  tears  which  keep  the  eye  moist. 
Unless  provided  against,  this  exposure  of  the  eye  may  result  in 
injury  (p.  519). 

(3)  Effect  of  Facial  Paralysis  on  the  Mouth. — The   mouth  is 
drawn  by  the  unparalyzed  muscles  to  the  unaffected  side.     It  is 
impossible  to  approximate  the  lips  of  the  affected  side  to  a  tumbler 
or  cup ;  consequently  in  drinking  therefrom,  unless  the  head  is 
thrown  back,  fluids  will  dribble  from  the  corners  of  the  mouth. 
The  buccinator  muscle  being  paralyzed,  food  finds  its  way  into 
the  space  between  the  cheek  and  the  gum,  and   mastication  is 
seriously  impeded.    The  lips  being  paralyzed,  the  consonants  b  and 
p  cannot  be  pronounced  distinctly.     If  the  tongue  is  protruded,  it 
seems  to  be  deviated  toward  the  affected  side ;  but  this  is  only  ap- 
parent, for  if  the  mouth  is  placed  in  the  normal  position  it  will 
be  seen  that  the  tongue  is  unaffected. 

(4)  Effect  of  Facial  Paralysis  on  Taste. — Accompanying  facial 
paralysis  may  be  impairment  or  abolition  of  the  sense  of  taste. 
Authorities  are  not  agreed  as  to  the  explanation  of  this  result,  but 
it  is  doubtless  due  to  interference  with  the  chorda  tympani.    Some 
attribute  it  to  the  influence  which  this  nerve  exercises  over  the 
circulation  in  the  tongue  and  on  the  secretion  of  saliva :  others 
regard  the  chorda  tympani  as  the  nerve  of  taste  to  the  anterior 
two-thirds  of  the  tongue,  and  as  taking  part  in  forming  the  gusta- 
tory nerve  or  lingual  branch  of  the  trigeminus.     Indeed,  there  is 
a  difference  of  opinion  among  anatomists  as  to  the  true  source  of 
the  chorda  tympani,  at  least  so  far  as  concerns  those  fibers  which 


THE  BRAIN.  523 

are  connected  with  the  sense  of  taste ;  some  look  upon  it  as  a  part 
of  the  fifth,  some  as  a  part  of  the  seventh,  and  still  others  as  a 
part  of  the  ninth  or  glossopharyngeal. 

Auditory. — The  auditory  nerve  has  its  apparent  origin  from  the 
lower  border  of  the  pons,  in  the  groove  between  the  olivary  and 
restiform  bodies.  Its  real  origin  is  in  the  floor  of  the  fourth 
ventricle.  As  already  stated,  the  auditory  nerve  enters  the  in- 
ternal auditory  meatus  with  the  facial  nerve.  It  is  distributed  to 
the  internal  ear,  and  is  the  special  nerve  of  the  sense  of  hearing. 
It  will  further  be  discussed  in  connection  with  that  special  sense. 

Glossopharyngeal. — The  superficial  origin  of  the  glossopharyn- 
geal nerve  is  from  the  upper  part  of  the  medulla,  in  the  groove 
between  the  olivary  and  restiform  bodies.  Its  real  origin  is  a 
nucleus  in  the  lower  part  of  the  floor  of  the  fourth  ventricle. 
It  escapes  from  the  cranium  through  the  jugular  foramen,  together 
with  the  pneumogastric  and  spinal  accessory  nerves.  Its  branches 
of  communication  are  with  the  pneumogastric,  facial,  and  sympa- 
thetic nerves.  The  glossopharyngeal  gives  off  the  tympanic 
branch,  the  nerve  of  Jacobson,  which  is  distributed  to  the  fenestra 
rotunda,  the  fenestra  ovalis,  and  the  lining  membrane  of  the  tym- 
panum and  Eustachian  tube.  As  its  name  implies,  the  glosso- 
pharyngeal is  distributed  to  the  tongue  and  pharynx.  The  glossal 
portion  supplies  the  mucous  membrane  of  the  posterior  third  of 
the  tongue,  the  tonsils,  and  the  pillars  of  the  fauces  and  soft 
palate,  while  the  pharyngeal  portion  is  distributed  to  the  pharyn- 
geal  mucous  membrane  and  to  the  muscles  concerned  in  a  part  of 
the  act  of  deglutition — namely,  the  styloglossus,  digastric,  and 
stylopharyngeus,  and  the  superior  and  middle  constrictors. 

Physiologic  Properties. — The  sensibility  of  the  parts  to  which 
the  glossopharyngeal  nerve  is  distributed  is  due  to  this  nerve. 
It  is  also  a  nerve  of  special  sense,  supplying  the  posterior  third 
of  the  tongue  and  the  palate  with  the  sense  of  taste ;  and,  finally, 
it  is  the  motor  nerve  for  the  muscles  enumerated  which  are  con- 
cerned in  passing  the  food  from  the  back  of  the  mouth  into  and 
through  the  pharynx  to  the  esophagus  in  the  act  of  deglutition. 

Vagus. — This  nerve  is  also  called  pneumogastric,  from  two  of 
the  important  organs,  the  lungs  and  stomach,  to  which  it  is  dis- 
tributed. Its  apparent  origin  is  by  eight  or  ten  filaments  from 
the  groove  below  the  glossopharyngeal,  while  its  deep  origin  is 
from  a  nucleus  in  the  floor  of  the  fourth  ventricle,  below  and  con- 
tinuous with  that  of  the  same  nerve. 

At  the  jugular  foramen,  by  which  it  escapes  from  the  cranium, 
is  found  the  ganglion  of  the  pneumogastric  or  the  jugular  ganglion. 
The  pneumogastric  receives  branches  from  the  spinal  accessory, 
facial,  hypoglossal,  and  anterior  branches  of  the  first  and  second 
cervical  nerves.  It  assists  in  forming  the  pharyngeal,  laryngeal, 
pulmonary,  and  esophageal  plexuses.  Among  its  important 
branches  are  the  superior  and  inferior  laryngeal  nerves,  the  cardiac 


524 


THE  NERVOUS  SYSTEM. 


FIG.  307. — View  of  the  glossopharyngeal,  pneumogastric,  spinal  accessory,  and 
hypoglossal  nerves  of  the  left  side :  1,  pneumogastric  nerve  in  the  neck  ;  2,  ganglion 
of  its  trunk  ;  3,  its  union  with  the  spinal  accessory  ;  4,  its  union  with  the  hypoglossal ; 
5,  pharyngeal  branch :  6,  superior  laryngeal  nerve ;  7,  external  laryngeal ;  8,  laryn- 
geal plexus;  9,  inferior  or  recurrent  laryngeal;  10,  superior  cardiac  branch;  11, 
middle  cardiac;  12,  plexiform  part  of  the  nerve  in  the  thorax;  13,  posterior  pul- 
monary plexus;  14,  lingual  or  gustatory  nerve  of  the  inferior  maxillary;  15,  hypo- 
glossal,  passing  into  the  muscles  of  the  tongue,  giving  its  thyrohyoid  branch,  and 
uniting  with  twigs  of  the  lingual ;  16,  glossopharyngeal  nerve ;  17,  spinal  accessory 
nerve,  uniting  by  its  inner  branch  with  the  pneumogastric,  and  by  its  outer  passing 
into  the  sternomastoid  muscle ;  18,  second  cervical  nerve ;  19,  third  ;  20,  fourth  ;  21, 
origin  of  the  phrenic  nerve ;  22,  23,  fifth,  sixth,  seventh,  and  eighth  cervical  nerves, 
forming  with  the  first  dorsal  the  brachial  plexus;  24,  superior  cervical  ganglion  of 
the  sympathetic ;  25,  middle  cervical  ganglion :  26,  inferior  cervical  ganglion  united 
with  the  first  dorsal  ganglion  ;  27,  28,  29,  30,  second,  third,  fourth,  and  fifth  dorsal 
ganglia  (from  Sappey,  after  Hirschfeld  and  Leveille). 

and  the  gastric  branches.     The  pharyngeal  branch  is  distributed 
to  the  mucous  membrane  and  muscles  of  the  pharynx  and  to  the 


THE  BRAIN.  525 

muscles  of  the  soft  palate.  Its  esophageal  branches  supply  the 
mucous  membrane  and  muscular  coat  of  the  esophagus,  so  that 
the  act  of  deglutition,  which  begins  in  the  mouth  and  is  continued 
in  the  pharynx,  is  completed  by  the  esophagus.  The  superior 
laryngeal  nerve  is  distributed  to  the  cricothyroid  muscle  and 
to  the  inferior  constrictor,  and  communicates  with  the  superior 
cardiac  nerve.  Its  further  distribution  is  to  the  mucous  membrane 
of  the  epiglottis  and  larynx  as  far  as  the  vocal  cords. 

The  superior  laryngeal  nerve  is  the  sensitive  nerve  of  the 
larynx.  This  sensibility  is  of  great  importance  as  a  protection 
of  the  larynx  and  the  respiratory  organs  below  it  from  the  entrance 
of  foreign  bodies,  which  would  set  up  dangerous  inflammatory 
processes.  The  instant  such  a  substance  touches  the  surfaces  sup- 
plied by  this  nerve  a  violent  expulsive  cough  occurs  which  ejects  it. 
If  the  nerve  is  paralyzed,  as  it  may  be  after  diphtheria  or  in  con- 
nection with  brain  disease,  this  protection  is  absent,  and,  owing  to 
paralysis  of  the  cricothyroid,  the  ability  to  make  tense  the  vocal 
cords  is  lost  and  the  voice  is  hoarse. 

The  inferior  or  recurrent  laryngeal  nerve  is  distributed  to  all 
the  muscles  of  the  larynx  except  the  cricothyroid.  It  sends 
branches  to  the  mucous  membrane  and  muscular  coat  of  the 
esophagus,  to  similar  structures  of  the  trachea,  and  to  the  inferior 
constrictor.  It  is  the  motor  nerve  of  the  larynx,  and  may  be 
paralyzed  under  the  same  conditions  as  were  mentioned  in  con- 
nection with  the  superior  laryngeal,  and  all  motion  of  the  vocal 
cords  is  abolished.  One  nerve  may  alone  be  paralyzed,  as  when 
pressed  upon  by  a  tumor,  when  the  corresponding  vocal  cord 
would  alone  be  motionless. 

The  cardiac  branches  of  the  pneumogastric  terminate  in  the 
superficial  and  deep  cardiac  plexuses.  The  pulmonary  branches 
assist  in  forming  the  pulmonary  plexuses,  the  branches  of  which 
are  distributed  to  the  lungs.  The  esophageal  branches  form  the 
esophageal  plexus  or  plexus  guise.  The  gastric  branches,  which 
are  the  terminal  filaments  of  the  nerve,  are  distributed  to  the 
stomach  and  to  the  celiac,  splenic,  and  hepatic  plexuses,  the  latter 
two  supplying  the  liver  and  spleen. 

In  mentioning  some  of  the  branches  of  the  pneumogastric,  their 
functions  have  also  been  referred  to.  In  addition  to  these  func- 
tions the  movements  of  the  stomach  and  the  intestines  are  also 
performed  under  the  influence  of  this  nerve.  It  is  through  the 
cardiac  branches  that  the  inhibitory  impulses  from  the  medulla 
are  sent  to  the  heart.  Through  the  pulmonary  branches  impulses 
reach  the  respiratory  center  and  influence  respiration.  Reference 
has  previously  been  made  to  the  depressor  fibers,  which  run  in  the 
pneumogastric  to  the  vasomotor  center,  inhibiting  its  action  and 
thus  diminishing  the  work  of  the  heart. 

Spinal  Accessory  Nerve. — This  nerve  has  two  parts — one  arising 


526  THE  NERVOUS  SYSTEM. 

from  a  nucleus  in  the  medulla  below  that  of  the  pneumogastric, 
and  the  other  from  the  intermediolateral  tract  of  the  cord. 
The  former  is  the  accessory,  and  the  latter  the  spinal,  portion. 
The  accessory  portion  joins  the  pneumogastric,  and  is  distributed 
through  the  pharyngeal  and  superior  laryngeal  branches  of  that 
nerve.  It  is  also  probable  that  the  fibers  of  the  pharyngeal 
branch  going  to  the  muscles  of  the  soft  palate  are  fibers  of  this 
portion  of  the  spinal  accessory. 

The  inferior  laryngeal  nerve  also  contains  fibers  from  this 
nerve,  probably  from  the  internal,  anastomotic,  or  accessory  por- 
tion, and  experiments  demonstrate  that  the  power  which  the  larynx 
possesses  to  produce  vocal  sounds  is  due  to  these  fibers,  for  when 
the  spinal  accessory  is  torn  out  this  power  is  lost.  The  other  move- 
ments of  the  larynx,  those  which  take  place  during  respiration, 
are  not  interfered  with  under  these  circumstances,  but  only  those 
of  phonation-  The  inferior  laryngeal  nerve  is,  then,  only  par- 
tially made  up  of  spinal  accessory  fibers  :  these  fibers  preside  over 
phonation.  The  other  fibers,  which  are  probably  derived  from  the 
facial,  hypoglossal,  or  cervical,  or  all  of  them,  provide  the  nervous 
influence  for  the  other  movements.  If  the  entire  nerve  is  divided, 
the  laryngeal  movements  of  both  phonation  and  respiration  will  cease. 

The  spinal  or  external  portion  is  distributed  to  the  trapezius 
and  sternomastoid  muscles;  it  is  therefore  sometimes  called  the 
"  muscular  branch."  This  branch  is  believed  to  be  brought  into 
requisition  when  these  muscles  are  needed  for  more  than  their 
ordinary  activity,  for  the  nervous  force  to  supply  the  latter  is  fur- 
nished by  cervical  nerves.  In  unusual  straining  or  in  lifting,  or 
in  the  production  of  prolonged  cries,  these  muscles  are  brought 
into  action,  and  to  supply  the  additional  innervatiou  which  these 
acts  seem  to  require  is  believed  to  be  the  office  of  the  muscular 
branch  of  the  eleventh  nerve.  The  spinal  accessory  is,  then, 
a  motor  nerve,  although  some  writers  regard  a  portion  of  the 
fibers  of  the  accessory  part  as  being  sensory. 

Hypoglossal. — The  apparent  origin  of  this  nerve  is  by  filaments, 
from  10  to  15  in  number,  from  the  groove  between  the  pyramidal 
and  olivary  bodies :  its  real  origin  is  in  a  nucleus  in  the  floor  of 
the  fourth  ventricle.  It  sends  branches  of  communication  to  the 
pneumogastric,  the  sympathetic,  the  first  and  second  cervical,  and 
the  gustatory.  It  is  distributed  to  the  sternohyoid,  stern  othyroid, 
omohyoid,  thyrohyoid,  styloglossus,  hyoglossus,  geniohyoid,  and 
geniohyoglossus  muscles.  It  is  a  motor  nerve  to  the  tongue,  so 
much  so  that  it  has  been  called  the  "  motor  linguae."  The  move- 
ments over  which  it  presides  are  those  concerned  in  mastication 
and  deglutition  and  in  the  production  of  articulate  speech.  When 
this  nerve  is  paralyzed  on  one  side,  the  tongue,  when  protruded, 
is  directed  toward  the  paralyzed  side.  When  both  nerves  are 
involved  in  the  paralysis  all  motion  of  the  tongue  ceases. 


THE  SENSES.  527 


THE  SENSES. 

It  is  by  the  senses  that  the  individual  is  brought  into  relation 
with  the  world  outside  him.  The  senses  are  five  in  number  :  (1) 
General  sensibility;  (2)  Smell;  (3)  Taste;  (4)  Sight;  and  (5) 
Hearing. 

General  Sensibility. — This  kind  of  sensibility  is  so  called 
because  it  is  generally  distributed  over  the  entire  body  in  the 
skin,  and  in  those  parts  of  mucous  membrane  adjacent  to  the  skin. 
It  is  composed  of  a  variety  of  sensations  which  are  excited  by  a 
variety  of  stimuli,  but  it  is  still  an  unsettled  question  whether  the 
nerves  which  conduct  the  impulses  that  excite  these  sensations  are 
in  all  instances  the  ordinary  sensory  nerves  of  the  skin,  or  whether 
they  are  special  nerves,  each  one  conducting  only  its  own  special 
stimulus.  In  treating  of  the  subdivisions  of  general  sensibility 
this  question  will  again  be  referred  to. 

Sense  of  Touch. — The  sense  of  touch,  or  tactile  sensibility,  de- 
pends upon  the  existence  of  nerves  and  nerve-endings  (p.  64)  in 
the  skin  and  other  portions  of  the  body  in  which  the  function 
exists.  It  gives  knowledge  of  such  qualities  as  hardness  or  soft- 
ness, roughness  or  smoothness,  sharpness  or  dulness,  etc. ;  by  it 
we  become  acquainted  with  the  shape  and  consistency  of  objects, 
and  are  made  aware  of  the  presence  or  absence  of  irritating  quali- 
ties in  certain  substances.  The  pungent  vapors  of  some  gases 
excite  in  the  nose  the  ultimate  fibers  of  distribution  of  the  fifth 
pair  of  nerves,  and  not  those  of  the  first  pair,  and  it  is  incorrect 
to  describe  this  sensation  as  a  smell.  It  is  as  truly  a  tactile  sensa- 
tion as  when  a  sharp-pointed  instrument  is  brought  in  contact 
with  the  skin.  The  same  is  true  of  pungent  liquids  applied  to  the 
tongue,  which  are  commonly,  but  erroneously,  said  to  be  tasted. 

The  difference  in  the  tactile  sensibility  of  different  portions  of 
the  body  is  shown  in  the  following  table : 

TABLE  or  VARIATIONS  IN  THE  TACTILE  SENSIBILITY  or  DIFFERENT 

PARTS. 

The  measurement  indicates  the  least  distance  at  which  the  two  points  of  a 
pair  of  compasses  can  be  separately  distinguished  (E.  H.  Weber). 

Tip  of  tongue 1  mm. 

Palmar  surface  of  third  phalanx  of  forefinger     .....  2 

Palmar  surface  of  second  phalanges  of  fingers 4 

Red  surface  of  under  lip 4 

Tip  of  the  nose ' 6 

Middle  of  dorsum  of  tongue 8 

Palm  of  hand 10 

Center  of  hard  palate 12 

Dorsal  surface  of  first  phalanges  of  fingers 14 

Back  of  hand 25 

Dorsum  of  foot  near  toes 37 

Gluteal  region 37 

Sacral  region 37 


528  THE  NERVOUS  SYSTEM. 

* 

TABLE  OF  VARIATIONS,  ETC.— Continued. 

Upper  and  lower  parts  of  forearm 37  mm. 

Back  of  neck  near  occiput ...  50    ' 

Upper  dorsal  and  mid-lumbar  regions 50 

Middle  part  of  forearm 62 

Middle  of  thigh 62 

Mid-cervical  region 62 

Mid-dorsal  region 62 

Weber,  who  has  investigated  thoroughly  the  subject  of  tactile 
sensibility,  says  that  in  order  to  distinguish  the  two  points  of  the 
compasses  as  such,  there  must  be  unexcited  nerve-endings  between 
the  points  of  the  skin  that  are  touched  by  them,  and  the  greater 
the  number  of  these,  the  more  distinctly  are  they  recognized  as 
being  separate.  Tactile  sensibility  is  a  function  which  can  be 
educated  to  a  high  degree. 

Case  of  Laura  D.  Bridgman. — No  better  illustration  could  be 
given  of  the  degree  of  perfection  to  which  this  sense  can  be 
brought  than  that  of  the  deaf,  dumb,  and  blind  girl,  Laura 
Dewey  Bridgman.  When  about  two  years  old  this  child  had  scarlet 
fever,  as  a  result  of  which  she  lost  the  senses  of  sight,  hearing, 
taste,  and  smell.  Although,  about  eleven  years  after,  the  sense  of 
smell  returned  to  a  slight  degree,  the  other  senses  mentioned  were 
permanently  absent.  In  describing  her  case,  Prof.  Musscy,  Prof, 
of  Anatomy  and  Surgery  at  Dartmouth  College,  Hanover,  N.  H., 
where  Laura  lived,  states  that  she  possessed  not  merely  "  touch 
proper,"  but  the  capacity  for  "  acute  "  sensations,  pleasant  or  pain- 
ful ;  the  sensations  of  pressure,  weight,  temperature,  and  "  mus- 
cular sensations." 

In  speaking  of  this  girl,  her  instructor  said  :  "  With  regard  to 
the  sense  of  touch,  it  is  very  acute,  even  for  a  blind  person.  It 
is  shown  remarkably  in  the  readiness  with  which  she  distinguishes 
persons.  There  are  forty  inmates  in  the  female  wing,  with  all  of 
whom,  of  course,  Laura  is  acquainted  ;  whenever  she  is  walking 
through  the  passageways,  she  perceives  by  the  jar  of  the  floor  or 
the  agitation  of  the  air  that  some  one  is  near  her,  and  it  is  exceed- 
ingly difficult  to  pass  her  without  being  recognized.  Her  little 
arms  are  stretched  out,  and  the  instant  she  grasps  a  hand,  a  sleeve, 
or  even  a  part  of  the  dress,  she  knows  the  person,  and  lets  them 
pass  on  with  some  sign  of  recognition.  Her  judgment  of  dis- 
tances and  of  relations  of  place  is  very  accurate ;  she  will  rise 
from  her  seat,  go  straight  toward  a  door,  put  out  her  hand  just  at 
the  right  time,  and  grasp  the  handle  with  precision." 

From  her  Life  and  Education  it  is  impossible  to  ascertain  what 
ability  Laura  possessed  of  distinguishing  colors.  Her  historian 
says  that  it  has  been  stated  that  she  could  tell  the  color  of  every- 
thing by  feeling,  but  that  this  is  not  true.  He  further  says  that 
fabulous  stories  have  been  told  of  the  power  of  the  blind  to  dis- 
tinguish color,  but  such  statements  could  not  be  made  of  those  in 


GENERAL  SENSIBILITY.  529 

the  institution  with  which  she  was  connected.  "  It  is  true  of  many 
totally  blind  that,  if  a  number  of  balls  of  worsted  of  various 
colors  are  given  them,  and  they  are  obliged  to  notice  them  care- 
fully in  order  to  use  them  in  their  proper  places  in  work,  they 
will  rarely  make  a  mistake.  So  we  may  give  them  pieces  of  silk, 
with  the  same  result ;  but  this  does  not  prove  that,  having  been 
told  the  colors  in  one  material  or  fabric,  they  will  recognize  them 
in  any  other. 

"  We  have  no  evidence  that  there  is  any  inherent  property  in 
the  color  red,  or  blue,  or  yellow,  which  will  enable  the  most  sensi- 
tive touch  to  detect  each  in  all  materials  offered." 

Sense  of  Pressure. — When  objects  are  laid  upon  the  hand  there 
is  a  sensation  produced,  which  is  that  of  pressure,  and  by  the  exer- 
cise of  this  sense  we  are  able  to  distinguish  differences  in  the 
weights  of  objects.  This  is  true  of  other  portions  of  the  body  as 
well  as  of  the  hand.  Sense  of  pressure  and  tactile  sensibility  are 
not  identical ;  indeed,  portions  of  the  body  in  which  the  latter  is 
very  acute  are  nevertheless  very  insensitive  to  pressure.  Thus  the 
tactile  sensibility  of  the  tip  of  the  tongue  is  very  highly  devel- 
oped, but  its  sense  of  pressure  is  very  deficient.  Kirkes  says  that 
with  the  tip  of  the  tongue  one  cannot  detect  the  radial  pulse. 
While  there  is  a  marked  difference  between  the  tongue  and 
the  finger  in  their  ability  to  distinguish  the  pulse-beats,  still  the 
writer  is  positive  that  the  statement  that  these  cannot  be  felt  by 
the  tongue  is  not  true  for  all  individuals. 

It  is  to  be  borne  in  mind  that  in  the  investigation  of  the  sense 
of  pressure  the  muscles  must  not  be  brought  into  play,  otherwise 
a  new  factor  is  involved — the  muscular  sense. 

Muscular  Sense. — This  sense  is  brought  into  action  in  lifting 
weights,  and  the  estimation  of  the  weight  of  an  object  depends 
upon  the  amount  of  nervous  energy  (efferent  impulses)  necessary 
to  accomplish  the  result.  Some  authorities  regard  it  as  a  modifica- 
tion of  the  sense  of  pressure ;  but  the  two  senses  are  undoubtedly 
distinct. 

Sense  of  Temperature. — By  this  sense  the  difference  in  tem- 
perature of  bodies  is  recognized,  and  it  is  a  well-known  fact  that 
the  various  portions  of  the  body  are  endowed  with  different 
degrees  of  sensibility  in  this  regard  :  The  hand  will  bear  a  degree 
of  heat  which  would  cause  great  pain  to  some  other  parts  of  the 
body.  The  sense  of  temperature  and  that  of  touch  are  entirely 
distinct,  and  this  fact  may  readily  be  demonstrated  by  pressing 
firmly  on  a  sensitive  nerve*  until  the  part  to  which  it  is  distributed 
is  almost  devoid  of  the  sense  of  touch,  when  it  will  be  found  that 
the  sense  of  temperature  is  unaffected. 

Not  only  is  the  sense  of  temperature  distinct  from  other  sensa- 
tion, but  even  this  is  so  subdivided  that  there  are  heat  spots  and 
cold  spots — that  is,  portions  of  the  skin  which  are  excited  by  heat 

34 


530 


THE  NERVOUS  SYSTEM. 


and  cold  respectively.  Thus  if  a  heated  object  is  moved  about 
over  the  skin,  at  some  points  tactile  sensibility  alone  will  be 
excited,  while  at  others  the  object  will  feel  distinctly  hot.  In 
like  manner  cold  spots  will  be  recognized  by  the  application  of  a 
cold  object.  This  test  applied  to  the  skin  of  the  forearm  has 
resulted  in  such  a  chart  as  is  shown  in  Fig.  308. 

Sense  of  Pain. — When  the  stimuli  that  call  out  the  sense  of 
touch  or  of  temperature  are  excessive,  the  sense  of  pain  is  pro- 
duced, and  the  other  sensations  are  abolished  ;  thus  when  a  piece 


HI!!* 


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P^^^iiiilliWTllPil!!! 


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FIG.  308. — Cold  and  hot  spots  from  the  same  part  of  the  anterior  surface  of  the 
forearm :  o,  cold-spots ;  6,  hot-spots.  The  dark  parts  are  the  more  sensitive ;  the 
hatched  the  medium ;  the  dotted  the  feehle ;  and  the  vacant  spaces  the  non- 
sensitive. 

of  iron  very  much  heated  burns  the  hand,  the  sensation  is  the 
same  as  when  the  iron  is  very  cold. 

Some  authorities  regard  the  sense  of  pain  as  being  a  distinct 
sensation,  others  as  simply  an  exaggeration  of  other  sensations. 

Sense  of  Smell. — In  the  consideration  of  the  respiratory 
processes  the  nose  was  described  as  being  a  part  of  the  respiratory 
tract  (p.  353).  This  is  true  of  the  lower  portion  of  the  nasal 
cavity,  the  entrance  or  regio  vestibularis  and  the  regio  respiratoria, 
the  rest  of  the  lower  part  of  the  nasal  cavity;  the  upper  part, 
however,  is  more  especially  concerned  with  the  function  of  smell, 
and  is  therefore  called  regio  olfactoria.  This  portion  of  the  mucous 
membrane  is  sometimes  denominated  olfactory  membrane,  and  may 
be  defined  as  that  portion  of  the  Schneiderian  membrane  which 
covers  the  superior  and  middle  turbinated  bones  and  the  upper 
part  of  the  septum  nasi.  The  Schneiderian  membrane  lines  the 
nasal  fossae.  Before  the  time  of  Schneider,  from  whom  the  mem- 


SENSE  OF  SMELL. 


531 


brane  was  named,  it  was  thought  that  the  secretion  it  forms  came 
from  the  brain  :  he  demonstrated  that  it  came  from  the  membrane 
itself.  It  is  covered  by  epithelium,  which,  near  the  orifice  of  the 
nostril  in  the  vestibule,  is  pavement,  but  elsewhere,  except  on  the 
olfactory  membrane,  this  epithelium  is  columnar  and  ciliated. 
In  man  the  olfactory  membrane  is  soft,  vascular,  and  of  a  yellow 
color.  It  is  covered  by  epithelium  composed  of  two  varieties  of  cells, 
with  a  superficial  lamina  through  which  the  ends  of  the  cells  pro- 
ject. One  variety,  olfactory  or  olfactorial  celts,  is  spindle-shaped 
and  bipolar  (Fig.  309),  having  a  nu-  &*fs*&&ssll!^^ 
cleus.  One  of  the  poles  extends  to  the  ***^3f^Y*tf^ 

surface,  its  extremity  passing  through  i    •    [,,  j    jj  i 

the  lamina,  and  in  amphibia,  reptiles, 
and  birds  terminates  in  fine,  hair-like 
filaments.  It  is  uncertain  whether 
these  filaments  exist  in  mammals. 
The  other  pole  extends  downward 
and  is  connected  with  one  of  the 
fibrils  of  the  olfactory  nerve,  and 
passes  through  the  cribriform  plate 
of  the  ethmoid  bone,  and  arborizes 
within  one  of  the  olfactory  glomeruli 
(Fig.  310).  The  other  variety  of  cells 
is  the  columnar  or  sustentacular  cell. 
These  are  columnar  epithelium-cells 
with  nucleated  cell-bodies  at  the  free 
surface  of  the  mucous  membranes  and 
branching  processes  extending  down- 
ward :  they  are  supporting  cells.  The 
corium  of  the  olfactory  membrane 
is  very  thick  and  vascular,  with 
bundles  of  olfactory  nerve-fibers  and 
a  large  number  of  serous  glands,  Bow- 
man's glands,  whose  ducts  open  upon 
the  surface  of  the  membrane  between 
the  epithelial  cells. 

Olfactory  Nerves. — These  are  about 
twenty  in  number,  non-medullated,  and  are  given  off  from  the 
olfactory  bulb.  They  pass  through  the  cribriform  plate  of  the 
ethmoid  bone  and  are  distributed  to  the  olfactory  membrane. 

Olfactory  Bulb. — This  is  in  reality  a  portion  of  the  hemispheres, 
and  is  described  as  "  a  cap  superimposed  upon  a  conical  process 
of  the  cerebrum."  It  consists  of  gray  and  white  matter,  and  is 
thus  described  by  Schafer :  "  Dorsally  there  is  a  flattened  ring 
of  longitudinal  white  bundles  enclosing  neuroglia,  as  in  the 
olfactory  tract ;  but  below  this  ring  several  layers  are  recognized, 
as  follows : 


FIG.  309. — Olfactory  mucous 
membrane :  a,  sustentacular 
cells ;  6,  olfactory  cells  ;  c,  basal 
cells;  d,  submucous  fibrous  tis- 
sue ;  e,  glands  of  Bowman  ;  I, 
nerve-fibers  (Leroy). 


532 


THE  NERVOUS  SYSTEM. 


"  1.  A  white  or  medullary  layer,  characterized  by  the  presence 
of  a  large  number  of  small  cells  (' granules')  with  reticulating 
bundles  of  medullated  nerve-fibers  running  longitudinally  between 
them. 

"  2.  A  layer  of  large  nerve-cells,  with  smaller  ones  intermingled, 
the  whole  embedded  in  an  interlacement  of  fibrils  which  are 
mostly  derived  from  the  cell-dendrons.  From  the  shape  of  most 
of  the  large  cells  of  this  layer  it  has  been  termed  the  i  mitral ' 
layer.  These  cells  send  their  neurons  upward  into  the  next  layer, 


olf.c. 


FIG.  310.— Diagram  of  the  connections  of  cells  and  fibers  in  the  olfactory  bulb: 
olf.c,  cells  of  the  olfactory  mucous  membrane;  olf.n,  deepest  layer  of  the  bulb, 
composed  of  the  olfactory  nerve-fibers  which  are  prolonged  from  the  olfactory 
cells ;  gl,  olfactory  glomeruli,  containing  arborization  of  the  olfactory  nerve-fibers 
and  of  the  dendrons  of  the  mitral  cells ;  m.c,  mitral  cells ;  a,  thin  axis-cylinder 
process  passing  toward  the  nerve-fiber  layer,  n.tr,  of  the  bulb  to  become  continuous 
with  fibers  of  the  olfactory  tract ;  these  axis-cylinder  processes  are  seen  to  give  off 
collaterals,  some  of  which  pass  again  into  the  deeper  layers  of  the  bulb ;  n',  a  nerve- 
fiber  from  the  olfactory  tract  ramifying  in  the  gray  matter  of  the  bulb  (Schafer). 

and  they  eventually  become  fibers  of  the  olfactory  tract  and  pass 
along  this  to  the  base  of  the  brain,  giving  off  numerous  collaterals 
in  the  bulb  as  they  pass  backward. 

"  3.  The  layer  of  olfactory  glomeruli  consists  of  rounded  nest- 
like  interlacements  of  fibrils  which  are  derived  on  the  one  hand 
from  the  terminal  arborizations  of  the  non-medullated  fibers 
which  form  the  subjacent  layer,  and  on  the  other  hand  from 
arborizations  of  descending  processes  of  the  large  i  mitral '  cells 
of  the  layer  above. 

"4.  The  Layer  of  Olfactory  Nerve-fibers. — These  are  all  non- 


SENSE  OF  SMELL.  533 

medullated,  and  are  continued  from  the  olfactory  fibers  of  the 
Schneiderian  or  olfactory  mucous  membrane  of  the  nasal  fossae. 
In  this  mucous  membrane  they  take  origin  from  the  bipolar 
olfactory  cells  which  are  characteristic  of  the  membrane,  and  they 
end  in  arborizations  within  the  olfactory  glomeruli,  where  they 
come  in  contact  with  the  arborizations  of  the  mitral  cells." 

Olfactory  Tract. — This  structure  is  an  outgrowth  from  the  brain, 
which  is  in  man  at  one  period  of  development  hollow,  but  later 
the  cavity  is  filled  with  neuroglia,  outside  of  which  are  bundles  of 
white  fibers,  and  still  more  external  is  a  layer  of  neuroglia.  There 


Mitral  cells. 


f  Large 

i  nerve- 
cell 
Small 
nerve- 
cell. 


Layer  of  olfactory 
glomeruli. 


Peripheral  nerve- 
fibers. 


FIG.  311.— The  olfactory  bulb,  after  Golgi  and  Eamon  y  Cajal.    The  granular  layer 

is  not  shown. 

are  no  nerve-cells  in  the  tract.  It  lies  in  the  olfactory  sulcus,  a 
depression  in  the  under  surface  of  the  frontal  lobe  of  the  cere- 
brum, and  terminates  in  the  olfactory  bulb.  Traced  backward, 
the  tract  is  found  to  be  made  up  of  two  roots,  external  and  in- 
ternal ;  between  these  is  the  trigonum  ol/actorium,  which  is  some- 
times called  the  middle  or  gray  root,  but  which  is  in  reality  cortical 
gray  matter.  The  external  root  is  connected  with  the  end  of  the 
hippocampal  gyrus,  and  the  internal  with  the  beginning  of  the 
gyrus  fornicatus. 

Functions  of  the  Olfactory  Nerves. — The  olfactory  nerves  are 
beyond  all  doubt  the  channels  by  which  olfactory  impressions 
reach  the  brain  (Fig.  312).  They  are  nerves  of  the  special  sense 


534  THE  NERVOUS  SYSTEM. 

of  smell.  The  whole  mucous  membrane  of  the  nose  is  not  sup- 
plied with  olfactory  fibers ;  hence  only  in  that  part  where  they  are 
present,  the  olfactory  membrane,  does  the  sense  of  smell  reside. 
The  proof  that  the  function  of  these  nerves  is  that  of  smell  is 
derived  from  experiments  upon  lower  animals  and  from  observa- 
tions upon  man.  Animals  whose  sense  of  smell  is  very  acute  have 
the  olfactory  bulbs  and  tracts  more  highly  developed— that  is, 
these  structures  are  larger— than  in  those  animals  in  which  the 
acuteness  of  the  sense  of  smell  is  not  marked.  If  the  tracts  are 
destroyed,  the  sense  of  smell  is  abolished.  Although  this  experi- 


FIG.  312 . — Nerves  of  the  outer  walls  of  the  nasal  fossse :  1,  network  of  the 
branches  of  the  olfactory  nerve,  descending  upon  the  region  of  the  superior  and 
middle  turbinated  bones ;  2,  external  twig  of  the  ethmoidal  branch  of  the  nasal 
nerves ;  3,  sphenopalatine  ganglion  ;  4,  ramification  of  the  anterior  palatine  nerves ; 
5,  posterior,  and  6,  middle,  divisions  of  the  palatine  nerves ;  7,  branch  to  the  region 
of  the  inferior  turbinated  bone ;  8,  branch  to  the  region  of  the  superior  and  middle 
turbinated  bones;  9,  nasopalatine  branch  to  the  septum  cut  short  (from  Sappey, 
after  Hirschfeld  and  LeveillS). 

mental  proof  is  not  applicable  in  man,  still  there  are  cases  on 
record  in  which  an  absence  of  the  sense  of  smell  during  life  has 
been  found  after  death  to  have  accompanied  an  absence  of  the 
olfactory  tracts ;  and  there  are  cases  also  of  individuals  whose 
sense  of  smell  has  been  seriously  impaired  after  injury  to  the  tracts. 
During  ordinary  respiration  the  inspired  air  does  not  pass  over 
the  olfactory  membrane,  but  only  over  the  lower  part  of  the 
Schneiderian  membrane,  the  respiratory  portion.  Hence  if  odors 
are  faint,  they  are  not  detected,  unless  by  a  strong  inspiration  the 
air  is  carried  up  to  and  over  that  portion  to  which  the  olfactory 
nerves  are  distributed.  If  the  nasal  passages  are  closed  by  a 
catarrhal  condition,  the  sense  of  smell  is  obtunded  or  may  even 
be  abolished  temporarily. 


SENSE  OF  TASTE.  535 

'  It  is  important  to  distinguish  between  the  sense  of  smell  and 
general  sensibility.  The  mucous  membrane  of  the  nose  has,  in 
common  with  other  mucous  membranes  and  the  skin,  th$  power 
to  recognize  such  physical  properties  in  objects  as  consistency, 
temperature,  etc.  Thus  if  a  sharp  instrument  was  to  be  brought 
in  contact  with  this  membrane,  it  would  be  recognized  as  sharp, 
but  this  recognition  is  not  due  to  the  excitation  of  the  olfactory 
nerves,  but  to  the  fibers  of  the  trigeminus.  The  mucous  mem- 
brane is  therefore  supplied  by  two  nerves,  the  olfactory  and  the 
fifth.  One  is  not  liable  to  confound  sharpness  with  odor,  but  the 
irritating  effects  of  certain  substances  are  often  confounded  with 
the  sense  of  smell,  when,  as  a  matter  of  fact,  it  is  not  the  olfactory, 
but  the  fifth  pair,  which  is  excited.  Thus  if  acetic  acid  is  brought 
in  contact  with  the  mucous  membrane  of  the  nose,  it  will  excite 
the  fibers  of  the  fifth  pair  and  will  produce  an  irritating  effect, 
but  it  would  be  incorrect  to  say  that  we  smelled  it.  If,  however, 
vinegar  was  substituted  for  the  acetic  acid,  we  should  have  the 
irritating  effect  of  the  acetic  acid  it  contains,  and  in  addition  the 
olfactory  nerves  would  be  excited  by  the  aromatic  ingredients 
which,  with  the  acid,  form  vinegar ;  and  it  would  therefore  be  cor- 
rect to  say  that  we  smelled  the  vinegar. 

The  acuteness  of  the  sense  of  smell  differs  in  different  indi- 
viduals, but  in  most  it  is  well  marked.  It  has  been  estimated  that 
-g-Q  of  a  milligram  of  musk  may  be  detected  by  this  sense, 
le  emanations  from  objects  which  excite  the  sense  of  smell  pro- 
duce this  effect  by  stimulating  the  olfactory  cells,  and  the  impulses 
are  carried  by  the  olfactory  nerves  to  the  brain. 

Case  of  Julia  Brace. — A  remarkable  instance  of  the  acuteness 
of  the  sense  of  smell  is  that  of  Julia  Brace,  an  inmate  of  the 
Hartford  Asylum,  who  became  entirely  deaf  and  blind  at  the 
age  of  four  years  and  five  months.  The  history  of  this  case  is 
given  in  the  Life  and  Education  of  Laura  D.  Bridgman,  by 
M.  S.  Lamson.  This  girl  could  select  by  the  sense  of  smell  her 
own  clothes  from  a  mass  of  dresses  belonging  to  a  hundred  and 
thirty  or  forty  persons.  "She  could  discriminate,  merely  by 
smelling  them,  the  recently  washed  stockings  of  the  boys  at  the 
asylum  from  those  of  the  girls.  Among  a  hundred  and  twenty  or 
thirty  teaspoons  used  at  the  asylum  she  could  distinguish  those 
of  the  steward  from  those  of  the  pupils."  Her  sense  of  touch  was 
also  acute.  "  By  putting  the  eye  of  a  cambric  needle  upon  the  tip 
of  her  tongue,  she  could  feel  the  thread  as  it  entered  the  eye  and 
pressed  upon  her  tongue,  and  she  would  thus  thread  the  needle." 

Sense  of  Taste. — The  sense  of  taste  exists  to  a  slight  degree 
in  the  middle  of  the  dorsum  of  the  tongue,,  but  is  especially  de- 
veloped in  the  posterior  third  of  the  dorsum.  It  is  also  present 
in  its  tip  and  edges  and  in  the  soft  palate,  but  the  exact  area  in 
which  it  resides  has  never  been  determined. 


' 


:.,--    :   ..:,-          •    .-•-     --- 


538 


THE  NERVOUS  SYSTEM. 


branch  of  the  glossopharyngeal  nerve ;  the  apex  is  narrow  and 
communicates  with  the  cavity  of  the  mouth  by  a  small  pore  in  the 
superficial  epithelium — gustatory  pore. 

"  The  cells  which  compose  the  taste-buds  are  of  two  kinds, 
viz.:  1.  The  gustatory  cells,  which  are  delicate  fusiform  or  bipolar 
cells  composed  of  the  cell-body  or  nucleated  enlargement,  and  of 
two  processes,  one  distal,  the  other  proximal.  The  distal  process 
is  nearly  straight,  and  passes  toward  the  apex  of  the  taste-bud, 


•  Papilla  filiformis. 


' 


y  e&v-r-  Tongue  epithe- 
lium. 

• 


,v_  _  Connective-tissue 
papilla. 


*Ur-  Mucosa. 


ilV-J ,  Basal  epithelial 

layer. 

FlO.  315.— From  a  cross-section  of  the  human  tongue,  showing  short,  thread-like 
papillae  (filiform) ;  x  140  (Bohm  and  Davidoff). 

where  it  terminates  in  a  small,  highly  refracting  cilium-like 
appendage  which  projects  into  the  bottom  of  the  pore  above 
mentioned.  The  proximal  process  is  more  delicate  than  the 
other,  and  is  often  branched  and  varicose.  The  nerve-fibers  take 
origin  in  ramifications  among  the  gustatory  cells  (Retzius). 

"  2.  The  sustentacular  cells  (Fig.  318).— These  are  elongated 
cells,  mostly  flattened,  and  pointed  at  their  ends  ;  they  lie  between 
the  gustatory  cells,  which  they  thus  appear  to  support,  and  in 
addition  they  form  a  sort  of  envelope  or  covering  to  the  taste-bud. 


SENSE  OF  TASTE.  539 

Between  the  cells  of  the  taste-buds  lymph-corpuscles  are  often 
seen,  having  probably  wandered  hither  from  the  subjacent  mucous 
membrane." 


H 

J^Bi 

oftSPR 


FlG.  316. — Fungiform  papilla  from  human  tongue  (Huber). 

Fig.  319  shows  the  nerve-endings  in  the  taste-buds. 
The  fact  that  the  general  sensibility  of  the  tongue  may  be  lost 
and  the  sense  of  taste  remain  indicates  that  the  channels  for  the 


FIG.  317. — Longitudinal  section  of  foliate  papilla  of  rabbit,  showing  taste-buds 

(Huber). 

transmission  of  these  two  sensations  are  different.  It  may  be  well 
again  to  call  attention  to  the  necessity  for  making  a  distinction 
between  what  may  be  tasted  and  what  may  be  smelled,  between 
savors  and  flavors.  The  sense  of  taste  gives  cognizance  of  the 


540 


THE  NERVOUS  SYSTEM. 


Epithe- 
lium. 


Process  of 

neuro-epi- 

Nerve-       thelial   Taste- 
fibrils,       cell.        pore. 


.Tegmental 

cell. 
.Neuro-epithe- 

lial  cell. 

Sustentacular 
cell. 


Terminal 

1 branches    of 

nerves. 


FlG.  318.— Schematic  representation  of  a  taste-goblet  (partly  after  Hermann). 

qualities  sweet,  acid,  bitter,  and  saline;  but  to  speak  of  an  oily 
taste  is  incorrect:  such  a  quality  appeals  to  general  sensibility 
only.  The  tip  of  the  tongue  is  most  sen- 
sitive to  sweet  tastes,  the  sides  to  acid,  and 
the  back  to  bitter. 

Conditions  of  the  Sense  of  Taste. — That 
the  sense  of  taste  may  be  exercised  requires 
the  presence  of  certain  conditions,  one  of 
which  is  that  the  substance  must  be  in  a 
state  of  solution  or  be  soluble  in  the  saliva. 
Insoluble  substances  are  tasteless  :  for  this 
reason  calomel  is  especially  suitable  as  a 
cathartic  for  children.  Another  condition 
is  that  the  mucous  membrane  of  the  mouth 
must  be  moist.  When  the  mouth  is  dry 
and  substances  not  already  in  a  state  of 
solution  are  taken  in,  there  is  no  saliva 
present  to  dissolve  them ;  consequently 
they  are  not  tasted.  This  absence  of 
taste  is  very  marked  in  the  parched  con- 
dition of  the  mouth  occurring  during 
fevers. 

To  excite  the  sense  of  taste,  sapid  sub- 
stances must  pass  by  osmosis  into  the  pa- 
pillae of  the  mucous  membrane  and  there 
stimulate  the  terminal  filaments  of  the  nerves  which  preside  over 
this  sense.  An  important  agent  in  causing  this  absorption  is  the 


FIG.  319.— Nerve-endings 
in  taste-buds :  n,  nerve-fibers 
of  taste-buds,  6;  i,  ending 
of  fibrils  within  taste-bud  ; 
p,  ending  in  epithelium  be- 
tween taste-buds;  s,  surface 
epithelium  (G.  Eetzius). 


SENSE  OF  SIGHT.  541 

movement  of  the  tongue.  It  is  a  matter  of  common  observation 
that  if  sapid  substances  are  simply  placed  on  the  tongue,  the  sense 
of  taste  is  not  excited ;  but  if  the  tongue  is  pressed  against  the 
roof  of  the  mouth,  absorption  is  promoted  and  the  gustatory  qual- 
ities are  at  once  recognized. 

It  is  to  be  noted  also  that  a  savor  persists  for  a  certain  length 
of  time,  and  that  if  it  is  desired  to  determine  the  comparative 
qualities  of  different  substances  by  the  sense  of  taste,  there  must 
either  be  intervals  between  the  tests  or  something  must  be  used 
to  obliterate  the  taste  of  the  first  before  the  second  is  taken  into 
the  mouth.  It  is  also  noteworthy  that  some  savors  so  powerfully 
impress  the  taste-organs  that  others  subsequently  fail  to  make  any 
impression.  This  principle  is  made  practical  use  of  in  rendering 
disagreeable  medicines  tasteless.  Thus  a  few  cloves  eaten  before 
taking  a  dose  of  castor  oil  will  render  the  latter  far  less  nauseous ; 
a  mouthful  of  brandy  will  have  the  same  effect. 

Sense  of  Sight. — The  eyes  are  situated  in  the  orbits,  cavities 
formed  by  the  frontal,  sphenoid,  ethmoid,  superior  maxillary, 
malar,  lacrimal,  and  palate  bones.  Each  eye  is  embedded  in  fat 
and  enclosed  in  a  serous  sac,  the  capsule  of  Tenon  or  tunica 
vaginalis  oculi.  The  transverse  diameter  of  the  eye  'is  about  2.5 
cm.,  while  the  anteroposterior  and  vertical  diameters  are  about 
2.25  cm.  each. 

Coats  or  Tunics  (Fig.  320). — These  are  3  in  number :  (1)  Scle- 
rotic and  cornea ;  (2)  choroid,  ciliary  processes,  iris,  and  ciliary 
muscle ;  and  (3)  retina. 

Sclerotic. — This  tunic  forms  the  external  coat  of  the  eye  for  its 
posterior  five-sixths,  the  anterior  sixth  being  formed  by  the  cornea. 
The  sclerotic  is  opaque,  and  is  made  up  of  dense  fibrous  tissue 
with  elastic  fibers  and  connective-tissue  corpuscles,  and  the  white 
color  of  its  visible  external  surface  covered  by  conjunctiva  causes 
this  portion  to  be  known  as  the  white  of  the  eye.  The  internal 
surface  is  lined  by  connective  tissue,  in  which  are  brown  pigment- 
cells,  lamina  fusca.  This  inner  surface  is  grooved,  and  in  these 
grooves  lie  the  ciliary  nerves.  Posteriorly  and  on  the  nasal  side 
the  optic  nerve  pierces  the  sclerotic,  which  in  this  part  is  charac- 
terized by  small  openings,  through  which  the  fibers  composing  the 
optic  nerve  pass.  This  sieve-like  structure  has  given  to  the  scle- 
rotic at  this  point  the  name  lamina  cribrosa.  The  largest  of  these 
openings,  porus  options,  is  in  the  middle  of  the  lamina,  and 
through  it  passes  the  arteria  centralis  retinae  (Fig.  328,  A).  En- 
circling the  lamina  cribrosa  are  openings  in  the  sclerotic  through 
which  pass  the  ciliary  vessels  and  nerves.  Supplying  the  sclerotic 
itself,  nerves  have  not  been  demonstrated. 

Cornea. — This  structure  is  transparent,  and  its  relation  to  the 
sclerotic  has  been  compared  to  that  of  a  watch-crystal  to  the 


542 


THE  NERVOUS  SYSTEM. 


watch  itself.  It  is  the  segment  of  a  smaller  sphere  than  the 
sclerotic.  Its  anterior  surface  is  convex  and  covered  by  conjunc- 
tiva, its  posterior  surface  concave,  the  curvature  being  less  in  old 
age.  It  is  composed  of  four  layers  (Fig.  321) :  (1)  Stratified  epi- 
thelium, next  to  the  conjunctiva.  (2)  A  thin  layer  of  connective 
tissue,  membrane  of  Bowman.  (3)  Fibrous  connective  tissue,  proper 
substance  of  the  cornea,  which  is  made  up  of  fibers  arranged  in 
lamellse,  those  of  each  of  the  sixty  bundles  being  at  right  angles 
with  those  of  the  lamellae  above  and  below  it.  Between  the 


Blood-vessels  Sphincter 

Vein.     Canal  of  Petit,    of  the  iris.    Cornea,     papillae.      Iris. 
\  I     -...•-  / 


Fontana's  spaces. 


Ciliary 


Physiologic  excavation. 


Macula  lutea. 


—  Pigmenl 
layer, 

~a 

\-b 

--  Sclera. 
'"  Choroid 


^Rectus 
muscle. 

Adipose 
tissue. 


FIG.  320. — Schematic  diagram  of  the  eye :  a,  vena  vorticosa ;  6,  choroid ;  I,  lens 
(after  Leber  and  Flemmiug). 

lamellae,  and  connecting  them,  is  a  cement  substance,  and  in  this 
are  the  stellate  corneal  spaces,  each  of  which  contains  a  corneal 
corpuscle,  which  gives  oif  branches  that  form  with  the  processes 
of  other  corpuscles  a  continuous  network.  This  third  layer  is  of 
the  same  character  as  the  sclerotic  coat,  and  is  continuous  with  it. 
(4)  Membrane  of  Descemet  or  Demours',  an  elastic  layer  which,  near 
the  junction  of  the  cornea  with  the  iris,  separates  into  fibers, 
ligamentum  pectinatum.  Some  of  these  exist  in  the  iris  as  its 
pillars.  The  fourth  layer  is  covered  by  pavement  epithelium, 
epithelium  of  Descemet' s  membrane.  This  epithelium  forms,  there- 


SENSE  OF  SIGHT. 


543 


fore,  the  most  posterior  portion  of  the  cornea,  and  inasmuch  as  the 
space  directly  behind  the  cornea  is  the  anterior  chamber,  this  epi- 
thelium forms  the  anterior  boundary  of  this  space.  These  epithelial 


Corneal 
epithelium, 


Basal  cells. 

Anterior 
elastic 
membrane 

Substantia 
propria. 


FIG.  321.  —  Section  through  the  anterior  portion  of  human  cornea  ;  X  500  (Bohm  and 

Davidoff). 


cells  are  continuous  with  those  covering  the  anterior  surface  of  the 
iris.    The  cornea  contains  no  blood-vessels,  these  ending  in  the  form 


Sclera.  < 


Lamina  supra- 
choroidea. 


Lamina  vascu- 
losa  Halleri. 


Lamina  chorio- 

capillaris. 
Glassy  layer.  " 
FIG.  322.— Section  through  the  human  choroid  ;  X  130  (Bohm  and  Davidoff). 

of  loops  at  its  circumference.  Nor  are  there  distinct  lymphatics, 
though  the  channels  which  lodge  the  nerves  are  believed  to  serve 
this  purpose.  Branches  of  the  ciliary  nerves  are  supplied  to  it, 


544  THE  NERVOUS  SYSTEM. 

varying  in  number  from  twenty-four  to  forty-five,  according  to 
different  authorities.  These  nerves  terminate  in  the  subepitheliat 
plexus,  beneath  the  superficial  epithelium,  from  which  fibers  pass 
to  the  cells  themselves,  forming  the  intra-epithelial  plexus. 

Choroid. — This  vascular  and  pigmented  structure  forms  the 
posterior  five-sixths  of  the  second  tunic  of  the  eye.  Its  anterior 
boundary  is  the  ciliary  ligament  formerly  so  called,  but  also  known 
as  the  ring  muscle  of  Mutter  ;  it  is  composed  of  the  circular  fibers 
of  the  ciliary  muscle.  Anterior  to  this  is  the  iris.  At  the  anterior 
margin  of  the  choroid  are  the  ciliary  processes.  The  inner  sur- 
face of  the  choroid  is  in  contact  with  the  retina. 

The  choroid  is  composed  of  three  layers:  (1)  lamina  supra- 
choroidea  (Fig.  322),  the  most  external,  consisting  of  connective 
tissue,  elastic  fibers,  pigment-cells,  and  lymph-corpuscles.  It  is 


Corneal  epithe- 
lium. 

Substantia  pro- 
1    pria. 


— Deseemet's 
membrane. 

Canal  of 
— ""    Schlemm. 

llris. 

;  Pigment-layer. 


--  Meridional  fibers.") 
-^~—  Radial  fibers.          h 
Miiller's  fibers.      { 


Sclera.  Processus  ciliares. 


FIG.    323.— Meridional    section   of   the    human    ciliary  body;    X20    (Bohm    and 

Davidoff). 

in  contact  with  the  lamina  fusca  of  the  sclerotic.  (2)  Vascular 
layer;  this  is  spoken  of  as  the  choroid  proper;  here  are  the 
blood-vessels  of  the  choroid,  consisting  externally  of  branches  of 
the  short  ciliary  arteries,  and  veins  arranged  in  a  vorticose, 
whorled,  or  star-like  form,  constituting  the  vence  vorticosce, 
which  converge  to  form  four  or  five  main  veins ;  between 
these  vessels  are  stellate  pigment-cells.  The  inner  portion  of  the 
vascular  layer  is  the  choriocapillaris  or  tunica  Ruyschiana,  a  plexus 
of  fine  capillaries  from  the  short  ciliary  vessels.  (3)  The  most 
internal  portion  of  the  choroid  is  the  lamina  vitrea,  glassy  layer,  or 
membrane  of  Bruch,  a  thin  membrane,  transparent,  and  ordinarily 
described  as  structureless,  although  Kolliker  considers  it  to  have  a 
fibrous  structure.  This  is  in  contact  with  the  pigmentary  layer 
of  the  retina. 

The  arteries  of  the  choroid  are  the  short  ciliary  and  the  recur- 


SENSE  OF  SIGHT.  545 

rent  branches  of  the  long  and  the  anterior  ciliary.  Its  nervous 
supply  is  the  long  and  short  ciliary  nerves. 

Ciliary  Processes  (Fig.  323).— The  vascular  layer  of  the  choroid 
with  the  lamina  vitrea  is  arranged  anteriorly  in  folds — the  ciliary 
processes.  These  fit  into  corresponding  folds  of  the  suspensory 
ligament  of  the  crystalline  lens.  Their  number  varies  from  sixty 
to  eighty  ;  some  being  about  0.25  cm.  in  length,  others  shorter.  In 
structure  they  are  like  the  choroid,  except  that  their  blood-vessels 
are  larger  and  are  longitudinally  arranged.  On  their  posterior 
surface  are  pigment-cells,  as  there  are  also  in  the  processes  them- 
selves. 

Iris. — This  is  a  muscular  and  vascular  structure  in  front  of  the 
crystalline  lens  and  behind  the  cornea.  In  its  center  is  a  circular 
opening — the  pupil.  Its  structure  is  not  unlike  that  of  the 
choroid,  and  on  its  anterior  surface  are  pigment-cells,  the  color  of 


FIG:  324.— Crystalline  lens  and  suspensory  ligament  or  zonula:  1,  lens;  2,  poste- 
rior, and  3,  anterior  portion  of  zonula  ;  4,  its  insertion  into  the  pre-equatorial  region. 
The  black  rays  are  lines  of  pigment  torn  from  the  ciliary  processes,  and  belong  in 
reality  to  the  ciliary  portion  of  the  retina  (Testut). 

whose  pigment  differs  in  different  individuals.  Its  posterior  sur- 
face is  covered  with  a  layer  of  pigmented  epithelial  cells,  the  uvea, 
which  is  continuous  with  those  of  the  pars  ciliaris  retinse. 

The  iris  is  composed  of  four  layers :  (1)  Most  anteriorly  is  a 
layer  of  cells  which  is  continuous  with  the  epithelium  of  Desce- 
met's  membrane,  and  in  these  there  is  pigment.  (2)  The  stroma  ; 
this  consists  of  fibrous  tissue,  the  fibers  of  which  at  the  margin  of 
the  pupil  are  circular,  elsewhere,  and  for  the  most  part,  radiating. 
Among  these  fibers  are  branched  cells,  containing  pigment  in 
persons  whose  eyes  are  dark,  while  in  light  eyes  the  pigment  is 
absent.  (3)  A  muscular  layer  consisting  of  the  sphincter  pupillce, 
which  is  composed  of  involuntary  fibers  circularly  arranged 
around  the  pupil,  and  having  a  width  of  about  0.08  cm.,  and  of 
the  dilator  pupillce,  composed  of  fibers  arranged  in  a  radiating 
direction.  (4)  The  pigmentary  layer  on  the  posterior  surface  of  the 

35 


546 


THE  NERVOUS  SYSTEM. 


Margin  of 

pupil. 


iris.  It  is  this  pigment  which,  as  seen  through  the  layers  of  the 
iris  anterior  to  it,  gives  the  color  to  light  eyes,  while  in  those 
having  dark  eyes  there  is,  besides,  pigment  in  the  fibrous  tissue  of 
the  stroma  and  on  the  anterior  surface  of  the  iris.  The  albino 
is  characterized  by  the  colorless  iris,  in  which  no  pigment  is 
present. 

The  arteries  which  supply  the  iris  are  branches  of  the  long 
and  anterior  ciliary,  which  together  form  the  circulus  iridis  major 
and  minor,  the  former  being  an  anastomotic  ring  at  the  outer 
margin  of  the  iris  ;  the  latter,  a  similar  one  near  the  pupil. 

The  nervous  supply  of  the  iris  is  derived  from  the  ciliary 

ganglion  and  •  from  the  nasal 
branch  of  the  ophthalmic 
division  of  the  fifth  nerve 
through  the  long  ciliary. 
The  branches  from  the  cil- 
iary ganglion  contain  fibers 
of  the  third  nerve,  which 
supply  the  circular  muscular 
fibers  or  sphincter  pupillse, 
and  also  sympathetic  fibers, 
which  are  distributed  to  the 
radiating  fibers  or  dilator  pu- 
pillae. 

Membrana  Pupillaris. — 
The  pupil  during  fetal  life, 
until  about  the  seventh  or 
eighth  month,  is  closed  by  a 
membrane.  At  this  time  it 
begins  to  be  absorbed,  and 
the  absorption  is  almost  en- 
tirely complete  at  birth. 

Ciliary  Muscle  (Fig.  323). 
— Like  the  muscular  fibers  of 
the  iris,  this  muscle  is  also 
of  the  unstriped  variety.  Its 
width  is  about  0.3  cm.,  and  it 
consists  of  two  parts,  a  ra- 
diating and  a  circular.  The  radiating  or  radial  fibers  are  the  more 
numerous,  and  have  their  origin  at  the  junction  of  the  cornea  and 
sclerotic,  sclerocorneal  junction,  and  passing  backward  are  attached 
to  the  choroid  opposite  the  ciliary  processes.  Waldeyer  states  that 
one  bundle  is  attached  to  the  sclerotic.  Internal  to  these  are  the 
circular  fibers,  running  around  the  attachment  of  the  iris,  called 
circular  ciliary  muscle,  ring  muscle  of  Mutter,  and  formerly  ciliary 
ligament.  These  fibers  are  said  to  be  most  marked  in  hyperme- 
tropic  eyes. 


Choroid. 


FIG.  325.— Injected  blood-vessels  of  the 
human  choroid  and  iris;  X  7  (Bohm  and 
Davidoff). 


SENSE  OF  SIGHT. 


547 


Ciliary  Body. — In  this  term  are  included  the  ciliary  muscle 
and  the  ciliary  processes. 

Retina. — This  is  the  most  internal  of  the  tunics  of  the  eye, 


FIG.  326.— The  normal  eye-ground  as  seen  with  the  ophthalmoscope :  n,  optic  nerve? 
head ;  m,  macula ;  a,  retinal  artery ;  v,  retinal  vein  (Pyle). 

and  is  divided  into  two  parts:    (1)   Pars  optica  retince,  which 
extends  as  far  forward  as  the  ciliary  body,  where  it  ends  in  an 


Layer  of 

nerve-fibers. 
Gangliou-cell- 
layer. 

Inner  molecu- 
lar layer. 
Inner  nuclear 

layer. 

Outer  molecu- 
lar layer. 
Outer  fibrous 
layer. 

Outer  nuclear 
layer. 

Cones. 


Fovea  centralis. 


FIG.  327.— Section  through  human  macula  lutea  and  fovea  centralis ;  X  150.  As 
a  result  of  treatment  with  certain  reagents,  the  fovea  centralis  is  deeper  and  the 
margin  more  precipitous  than  during  life  (Bohm  and  Davidoff). 

irregular  margin,  ora  serrata ;  (2)  pars  ciliaris  retince,  composed 
of  the  fibrous  stroma  of  the  retina  with  the  pigment-layer,  with- 


548 


THE  NERVOUS  SYSTEM. 


out  the  nervous  elements  present  in  the  pars  optica.     This  portion 
passes  forward  as  far  as  the  outer  margin  of  the  iris. 

Macula  Lutea  (Figs.  326,  327). — At  the  center  of  the  retina 
posteriorly,  and  at  the  posterior  extremity  of  the  axis  of  the  eye, 


FIG.  328.— Diagrammatic  representation  of  the  retina. 

is  the  macula  lutea,  yellow  spot  of  Sommerring,  or  limbus  luteus, 
having  a  diameter  of  from  1  to  2  mm.,  an  elevated  spot  in  the 
retina  where  the  sense  of  sight  is  most  acute ;  in  its  center  is  a 
depression,  the  fovea  centralis,  whose  diameter  is  from  0.2  mm. 


FIG.  329.— Schematic  diagram  of  the  retina,  according  to  Ramon  y  Cajal:  the 
line  a,  after  passing  through  a  Mailer's  fiber,  crosses  a  bipolar  rod-cell,  then  two 
bipolar  cone-cells,  and  finally  ends  in  the  body  of  a  bipolar  cone-cell,  a',  Nerve- 
fiber  layer ;  6,  ganglion-cell  layer ;  c,  inner  molecular  layer ;  d,  spongioblast ; 
e,  nucleus  of  Miiller's  fiber ;  /,  inner  nuclear  layer ;  g,  bipolar  cone-cell ;  h,  outer 
molecular  layer ;  i,  outer  nuclear  layer ;  fc,  cone ;  Z,  rod  ;  m,  centrifugal  nerve-fiber ; 
n,  impressions  on  Miiller's  fiber  of  elements  of  outer  nuclear  layer ;  o,  fiber  basket  of 
Miiller's  fiber;  p,  diffuse  spongioblast ;  q,  large  horizontal  cell ;  r,  bipolar  cell. 

to  0.4  mm.  At  the  fovea  the  retina  is  so  thin  that  the  color  of 
the  choroid  can  be  seen  through  it,  and  hence  it  has  somewhat  the 
appearance  of  an  opening,  and  was  formerly  called  foramen  of 
Sommerring.  For  further  discussion  of  the  macula  the  reader  is 
referred  to  p.  553. 


SENSE  OF  SIGHT. 


549 


Porus  Opticus  (Fig.  328).— About  3  mm.  to  the  nasal  side  of 
the  macula  lutea,  and  about  1  mm.  below  its  level,  is  the  optic  disk, 
the  entrance  of  the  optic  nerve ;  inasmuch  as  vision  is  absent  at 


Layer  of  nerve-    — 
fibers. 


Ganglion-cell  layer.   -- 


Inner  molecular  — • 
layer. 


Inner  nuclear  layer.  — 


Outer  molecular  -- 
layer. 


Outer  nuclear  layer.  —  •< 


Ext.  limiting  mem- 
brane. 
Inner  segment  of 

rod. 
Inner  segment  of 

cone. 

Outer  segment  of 

cone. 
Outer  segment  of 

rod. 


FIG.  330.— Section  of  the  human  retina;  X  700  (Bohm  and  Davidoff). 

this  point,  it  is  called  the  blind  spot.  At  its  center,  through  the 
porus  opticus,  enters  the  arteria  centralis  retince.  As  the  retina  is 
somewhat  elevated  at  the  blind  spot,  this  portion  of  it  has  also  re- 
ceived the  name  of  colliculus  nervi  optici. 


.  Lamina  cribrosa. 


Pigment-layer, 
and  cones. 


er  nuclea 

er  roolecu 

Layer  of  ner 


ayer. 
ar  'aver, 
layer, 
ar 'layer, 
e- fibers. 


Blood-vessels.        Physiologic  excavation. 

FIG.  331. — Section  through  point  of  entrance  of  human  optic  nerve ;  X  40  (Bohm  and 

Davidoff). 

The  arteria  centralis  retinae  is  a  branch  of  the  ophthalmid 
artery,  and,  after  piercing  the  porus  opticus,  it  divides  into  four  or 
five  branches  which  run  between  the  hyaloid  membrane  and  the 


550  THE  NERVOUS  SYSTEM. 

» 

nervous  layer  of  the  retina,  later  passing  into  the  retina  and 
ending  in  a  capillary  plexus  external  to  the  inner  nuclear  layer. 
During  fetal  life  a  small  artery  passes  forward  through  the 
vitreous  to  the  posterior  surface  of  the  capsule  of  the  lens.  In 
the  fovea  centralis  there  are  no  blood-vessels,  and  very  few  in  the 
rest  of  the  macula  lutea. 

Minute  Structure  of  the  Pars  Optica  Retince  (Figs.  329,  330, 
331). — The  pars  optica  of  the  retina  consists  of  ten  layers,  arranged 
in  the  following  order,  beginning  with  the  most  internal — L  e.,  with 
the  layer  next  to  the  hyaloid  membrane  which  encloses  the  vitreous 
humor — and  ending  with  the  most  external,  the  pigmentary  layer 
which  is  contiguous  to  the  lamina  vitrea  of  the  choroid  : 

1.  Membrana  limitans  interna; 

2.  Nerve-fiber  layer ; 

3.  Ganglionic  layer ; 

4.  Inner  molecular  layer ; 

5.  Inner  nuclear  layer ; 

6.  Outer  molecular  layer ; 

7.  Outer  nuclear  layer ; 

8.  Membrana  limitans  externa ; 

9.  Layer  of  rods  and  cones ; 
10.  Pigmentary  layer. 

1.  Membrana  Limitans  Interna. — This  is  a  transparent  mem- 
brane, and  a  part  of  the  supporting  connective  tissue  of  the  retina, 
or  the  fibers  of  Miiller,  in   connection  with   which  it  is  again 
referred  to  (p.  553). 

2.  Nerve-fiber  Layer. — This  is  sometimes  described  as  the  fibrous 
layer.    It  is  composed,  however,  of  nerve-fibers,  and  not  of  so-called 
fibrous  tissue.     The  fibers  of  which  it  is  composed  are  those  of  the 
optic  nerve,  and,  as  this  enters  the  eye  from  behind,  these  fibers 
must  pass  through  all  the  layers,  excepting  the  membrana  limitans 
interna,  in  order  to  reach  the  nerve-fiber  layer.     It  will  be  re- 
membered that  the  fibers  of  the  optic  nerve  pass  through   the 
lamina  cribrosa  of  the  sclerotic ;  at  this  part  of  their  course  their 
medullary  sheaths  disappear  and  they   become  simple  axis-cyl- 
inders, and  as  such  they  traverse  the  choroid  and  the  retina  until 
they  reach  the  nerve-fiber  layer,  where  they  radiate  from  the  point 
of  entrance  and  terminate,  some  in  the  cells  of  the  third  or  gan- 
glionic  layer,  while  others  pass  through  the  third  and  fourth  layers 
and  terminate  in  the  fifth  or  inner  nuclear  layer.     The  nerve-fiber 
layer  is  thickest  at  the  point  of  entrance  of  the  optic  nerve,  and, 
gradually  becoming  thinner,  ends  at  the  ora  serrata — i.  e.,  anterior 
to  this,  nerve-fibers  are  not  found  in  the  retina.     Or  this  may  be 
stated  in  another  way,  by  saying  that  nerve-fibers  are  found  in  the 
pars  optica  retinae,  but  not  in  the  pars  ciliaris  retinae. 

3.  Ganglionic  Layer. — This  is  called  also  vesicular  layer  and 
layer  of  nerve-cells,  and  consists  of  a  single  layer  of  large  ganglion- 


SENSE  OF  SIGHT.  551 

cells.  In  the  macula  lutea  the  cells  are  smaller,  and  lie  in  several 
layers.  The  shape  of  these  ganglion-cells-  is  peculiar,  resembling 
somewhat  those  of  Purkinje  in  the  cerebellum.  The  portion 
which  is  in  contact  with  the  nerve-fiber  layer  is  rounded,  and 
from  it  is  given  off  an  axis-cylinder  process  which  is  continuous 
with  one  of  the  axis-cylinders  which  make  up  the  nerve-fiber 
layer.  From  the  opposite  side  of  each  cell  is  given  off  a  thick 
process  which  branches,  the  branches  ending  in  arborizations  at 
different  levels  in  the  fourth  or  inner  molecular  layer. 

4.  Inner  Molecular  Layer. — This  is  called  also  inner  granular 
layer,  by  reason  of  its  granular  appearance,  and  also  reticular  layer. 
It  is  relatively  thick,  and  consists  of  a  reticulum  of  nerve-fibers 
with  interspersed  granules,  of  processes  of  the  cells  of  the  gan- 
glionic  layer,  and  of  those  of  the  inner  nuclear  layer. 

5.  Inner  Nuclear  Layer. — The  characteristic  elements  of  this 
layer  are  bipolar  nerve-cells  in   which  are   large   nuclei;   these 
cells  are  called  inner  granules.  ,  The   process   of  each  of  these 
cells  which  passes  inward  terminates  in  arborizations  in  the  inner 
molecular  layer ;  the  process  that  passes  outward  terminates  in  a 
similar  manner  in  the  outer  molecular'  layer.    There  are  two  kinds 
of  these  bipolar  cells :    (1)   Rod-bipolars  and   (2)   cone-bipolars. 
The  rod-bipolars  are  connected  externally  with  the  rods  of  the 
retina,  and  internally  with  the  rods  of  the  ganglionic  layer.     The 
cone-bipolars  are  connected  with  the  cones  of  the  retina  exter- 
nally, while  internally  they  ramify  in  the   middle  of  the  inner 
molecular  layer. 

In  addition  to  bipolar  cells  there  are  amacrine-cells,  so  called 
because  they  lack  long  processes,  although  from  some  of  them 
axis-cylinder  processes  are  given  off  which  may  extend  into  the 
nerve-fiber  layer.  The  bodies  of  these  cells  are  often  partly  in 
the  inner  molecular  layer,  and  they  are  sometimes  called  sportgio- 
blasts  of  the  inner  molecular  layer.  From  them  are  given  off 
branching  processes  or  dendrons  which  pass  into  the  inner  molec- 
ular layer. 

Horizontal  cells  of  Cajal  or  spongioblasts  of  outer  molecular 
layer  are  cells  in  this  layer  which  send  processes  into  the  outer 
molecular  layer. 

6.  Outer  Molecular  Layer. — This  is  a  thin  layer,  and  consists 
of  the  arborizations  of  the  inner  nuclear  layer,  of  the  rod-  and 
cone-fibers,  and  of  the  horizontal  cells  of  Cajal.     Schafer  states 
that  up  to  this  point — i.  e.,  including  the  outer  molecular  layer 
— the  retina  may  be  regarded  as  composed  of  nervous  elements, 
but  beyond  it  is  to  be  considered  as  formed  of  modified  epithe- 
lium-cells. 

7.  Outer  Nuclear  Layer. — In  this  layer  are  found  cells  charac- 
terized by  transverse  striations,  passing  off  from  which  externally 
are  processes  connected  with  the  rods  of  the  ninth  layer,  by  reason 


552  THE  NERVOUS  SYSTEM. 

of  which  arrangement  they  are  called  rod-granules.  These  gran- 
ules also  give  off  processes  which  pass  in  an  inward  direction  and 
terminate  in  the  outer  molecular  layer.  In  the  outer  nuclear  layer 
are  also  cone-granules ;  these  are  connected  with  the  cones  of  the 
ninth  layer  externally,  and  internally  by  a  thick  process  which 
becomes  bulbous,  the  so-called  cone-foot;  they  terminate  in  fine 
fibers  in  the  outer  molecular  layer. 

8.  Membrana  Limitans  Externa. — This  is,  together  with  the 
membrana  limitans  interna  and  the  fibers  of  Muller,  a  part  of  the 
supporting   structure   of  the   retina.      Indeed,   some   authorities 
include  neither  of  these  membranes  in  the  list  of  layers  which 
compose  the  retina,  and  hence  describe  it  as  made  up  of  eight 
rather  than  of  ten  layers. 

9.  Layer  of  Rods  and  Cones. — This  is  called  also  Jacob 's  mem- 
brane and  bacillary  layer.     It  is  characterized  by  the  presence  of 
rods  and  cones,  of  which  the  former  are  much  more  numerous1, 
taking  the  retina  as  a  whole.     Relatively  the  cones  are  more 
numerous  at  the  back  of  the  retina,  but  less  so  in  the  anterior 
part. 

Rods. — A  rod  is  a  solid  body  set  perpendicularly  to  the  sur- 
face at  whatever  part  of  the  retina  it  may  be.  It  is  made  up  of 
an  outer  and  an  inner  portion,  the  two  being  cemented  together. 
The  outer  portion  is  cylindrical  and  characterized  by  transverse 
striae  ;  it  has  during  life  a  purplish-red  color.  The  inner  portion 
has  striae  longitudinally  arranged.  This  portion  is  slightly  bulged, 
and  becomes  stained  with  carmine  or  iodin,  while  the  outer  portion 
does  not  take  the  stain. 

Cones. — Each  is  conical  in  form,  with  its  base  lying  on  the 
membrana  limitans  externa.  The  apex  is  tapering.  Like  the 
rods,  each  cone  is  made  up  of  an  outer  and  an  inner  portion ;  the 
outer  conical  apex  presenting  transverse  striae,  the  inner  portion 
being  striated  longitudinally.  Both  rods  and  cones  present  a 
granular  appearance  near  the  membrana  limitans  externa. 

Schafer  describes  the  outer  nuclear  layer  and  the  layer  of  rods 
and  cones  as  one,  under  the  name  sensory  or  nerve-epithelium 
of  the  retina,  inasmuch  as  their  elements  are  continuous  through 
the  two  layers.  He  says :  "  The  elements  of  which  this  nerve- 
epithelium  consists  are  elongated,  nucleated  cells  of  two  kinds. 
The  most  numerous,  which  we  may  term  the  rod-elements,  consist 
of  peculiar  rod-like  structures  (rods  proper)  set  closely  side 
by  side,  and  each  of  which  is  prolonged  internally  in  a  fine 
varicose  fiber  (rod-fiber)  which  swells  out  at  one  part  of  its 
course  into  a  nucleated  enlargement,  and  ultimately  ends  (in 
mammals)  in  a  minute  knob  within  the  outer  molecular  layer, 
where  it  is  embedded  in  the  ramifications  of  the  dendrons  of  the 
rod-bipolars.  The  rod  proper  consists  of  two  segments,  an  outer 
cylindrical  and  transversely  striated  segment,  which  during  life 


SENSE  OF  SIGHT.  553 

has  a  purplish-red  color,  and  an  inner  slightly  bulged  segment, 
which  in  part  of  its  length  is  longitudinally  striated.  The  nucleus 
of  the  rod-element  often  has,  in  the  fresh  condition,  a  transversely 
shaded  aspect.  The  cone-elements  are  formed  of  a  conical  tapering 
external  part,  the  cone  proper,  which  is  directly  prolonged  into  a 
nucleated  enlargement,  from  the  farther  side  of  which  the  cone- 
fiber,  considerably  thicker  than  the  rod-fiber,  passes  inward,  to 
terminate  by  an  expanded  arborization  in  the  outer  molecular 
layer ;  here  it  comes  into  relation  with  a  similar  arborization  of 
dendrons  of  a  cone-bipolar.  The  cone  proper,  like  the  rod,  is 
formed  of  two  segments,  the  outer  of  which,  much  the  smaller,  is 
transversely  striated,  the  inner,  bulged  segment  being  longitudi- 
nally striated.  The  inner  ends  of  the  rod-  and  cone-fibers  come, 
as  already  stated,  in  contact  with  the  peripheral  arborizations  of 
the  inner  granules,  and  through  these  elements  and  their  arbori- 
zations in  the  inner  molecular  layer  a  connection  is  brought  about 
with  the  ganglionic  cells  and  nerve-fibers  of  the  innermost  layers. 
There  appears,  however,  to  be  no  anatomic  continuity  between  the 
several  elements,  but  merely  an  interlacement  of  ramified  fibrils. 

10.  Pigmentary  Layer. — This  layer  is  called  also  tapetum 
nigrum,  and  consists  of  a  single  layer  of  hexagonal,  pigmented  cells 
in  contact  with  the  choroid.  These  cells  send  offsets  inward  be- 
tween the  rods.  The  pigment  is  in  the  form  of  minute  crystals, 
and  when  the  cells  have  been  exposed  to  light  for  a  considerable 
time  they  are  found  in  the  filaments  just  described  as  extending 
between  the  rods.  It  is  supposed  that  the  function  of  these  pig- 
ment-granules is  to  restore  the  purple  coloring-matter  which  has 
been  bleached  by  prolonged  exposure  to  light.  In  the  horse  and 
many  carnivora  these  cells  contain  no  pigment. 

Fibers  of  Mutter. — The  layers  of  the  retina  between  the  in- 
ternal and  external  limiting  membranes  are  traversed  by  long, 
stiff  cells,  the  fibers  of  Mutter.  At  their  bases  they  expand,  and 
the  tissue  joining  these  expanded  bases  forms  the  membrana 
limitans  interna.  At  the  outer  nuclear  layer  the  fibers  branch 
and  form  a  fenestrated  tissue  supporting  the  fibers  and  nuclei  of  the 
rod-  and  cone-elements.  At  the  junction  of  the  outer  nuclear  and 
bacillary  layers  the  fibers  form  the  membrana  limitans  externa, 
from  which  sheaths  pass  around  the  bases  of  the  rods  and  cones. 
In  that  portion  of  the  fiber  which  lies  in  the  inner  nuclear  layer 
is  an  oval  nucleus.  The  arrangement  of  these  fibers  of  Muller 
and  the  limiting  membranes  has  been  well  described  "  as  columns 
between  a  floor  and  a  ceiling." 

Macula  Lutea  (Figs.  326,  327).— The  retina  at  the  yellow  spot, 
except  at  the  fovea  centralis,  a  part  of  the  macula  lutea,  is  thicker 
than  elsewhere  ;  the  middle  of  the  fovea  is  the  thinnest  part  of  the 
retina.  The  ganglion-cells  are  more  numerous  in  the  macula,  as 
are  the  cones  when  compared  with  the  rods.  In  the  fovea  the  rods 


554  THE  NERVOUS  SYSTEM. 

are  absent,  and  the  cones  are  long  and  slender.  This  portion  of  the 
retina  consists  of  but  little  else  than  cones  and  the  outer  nuclear 
layer ;  the  cone-fibers  are  very  distinct  and  nearly  horizontal. 

Pars  Ciliaris  Retince. — At  the  ora  serrata  the  pars  optica 
retinae  terminates,  and  the  pars  ciliaris  retinae  begins.  It  consists 
of  two  layers :  An  external  layer  of  pigment-cells  which  are 
the  continuation  of  the  tapetum  nigrum,  and  an  internal,  of 
columnar  cells  with  oval  nuclei,  modified  fibers  of  Miiller.  The 
pigmented  epithelium  is  continuous  with  the  uvea  of  the  iris. 

The  sensory  epithelium  receives  its  nourishment  from  the 
blood-vessels  of  the  choroid. 

Anterior  and  Posterior  Chambers. — The  anterior  chamber  is  that 
portion  of  the  cavity  of  the  eye  situated  between  the  cornea  and 
the  iris ;  the  posterior  chamber,  the  space  between  the  iris  in  front ; 
and  the  capsule  of  the  lens,  the  suspensory  ligament  and  the  ciliary 
processes  behind.  Inasmuch  as  the  iris  is  in  contact  with  the 
capsule  for  the  greater  part  of  its  extent,  this  "  chamber "  is  ex- 
ceedingly small,  and  hardly  deserves  the  name.  In  fetal  life  these 
two  chambers  are  separated  by  the  membrana  pupillaris,  but  about 
the  seventh  or  eighth  month,  when  the  membrane  begins  to  be 
absorbed,  they  become  one  cavity,  and  are  filled  with  aqueous 
humor  (p.  556).  Some  authorities  describe  the  cavity  containing 
the  vitreous  under  the  name  "  posterior  chamber." 

Vitreous  Body. — This  is  called  also  vitreous  humor.  It  is  a 
transparent,  jelly-like  material  which  fills  the  cavity  of  the  retina 
and  is  enclosed  in  a  delicate  membrane,  the  hyaloid  membrane.  At 
the  pars  ciliaris  retinae  this  membrane  splits  into  two  layers,  an 
anterior  and  a  posterior.  The  anterior  layer  becomes  the  suspen- 
sory ligament  of  the  lens,  while  the  posterior  passes  behind  the 
lens  and  covers  the  anterior  portion  of  the  vitreous ;  at  this  part 
there  is  a  depression  in  the  vitreous  in  which  the  lens  lies.  In  the 
vitreous  are  found  fibers  and  some  cells,  the  bodies  of  which  con- 
tain large  vacuoles  and  give  off  long  and  varicose  processes. 
Through  its  center  in  fetal  life  runs  a  small  artery  from  the  arteria 
centralis  retinae  to  the  capsule  of  the  lens,  but  in  the  adult  this  is 
a  simple  channel,  canal  of  Stilling,  which  is  lined  by  a  portion  of 
the  hyaloid  membrane. 

Crystalline  Lens  (Fig.  332). — The  lens  is  a  transparent  body, 
biconvex  in  form,  the  convexity  being  greater  posteriorly  than 
anteriorly.  Its  transverse  diameter  is  about  0.8  cm.,  and  its 
anteroposterior  diameter  about  0.6  cm.  It  consists  of  concentric 
layers  or  lamina? ;  those  that  are  centrally  situated  form  the 
nucleus,  and  are  harder  than  the  external,  which  are  relatively 
soft.  If  the  lens  is  boiled  or  hardened  in  alcohol,  these  laminae 
may  be  peeled  off  like  the  coats  of  an  onion.  The  laminae  are 
composed  of  long  fibers  with  serrated  edges,  which  fit  into  corre- 
sponding serrations  of  adjoining  fibers.  When  cut  transversely, 


SENSE  OF  SIGHT. 


555 


the  fiber  is  seen  to  be  a  hexagonal  prism.  The  superficial  fibers 
contain  nuclei,  giving  to  the  external  layer  the  name  nucleated 
layer.  The  fibers  are  developed  from  epithelium-cells.  The 
centers  of  the  anterior  and  posterior  surfaces  are  the  poles,  and 
the  margin  of  the  lens,  where  these  surfaces  meet,  is  the  equator. 
During  fetal  life  the  lens  is 
nearly  spherical,  not  very  trans- 
parent, and  quite  soft  in  consist- 
ence ;  in  adult  life  its  posterior 
surface  is  more  convex  than  the 
anterior,  and  it  is  transparent. 
Its  consistence  has  already  been 
described.  In  old  age  its  con- 
vexity and  transparency  are 
diminished  and  its  density  in- 
creased. 

Capsule  .of  the  Lens. — This, 
like  the  lens,  is  transparent ;  it 
is  structureless  and  elastic.  At 
the  front  and  the  sides  of  the 
capsule  on  its  inner  surface  is 
a  layer  of  cubical  epithelium, 
the  epithelium  of  the  capsule. 
These  cells  are  elongated  at  the 
margin  of  the  lens  and  become 
lens-fibers.  This  epithelium  is 
absent  from  the  posterior  sur- 
face. The  suspensory  ligament 
is  attached  to  the  capsule  around 
its  circumference.  Anteriorly 
the  capsule  and  the  border  of 
the  iris  are  in  contact;  at  the 
circumference  they  are  slightly  separated,  the  space  thus  left  being 
the  posterior  chamber. 

Suspensory  Ligament. — This  is  the  anterior  part  of  the  hyaloid 
membrane  which  divides  into  two  layers  at  the  pars  ciliaris 
retinae.  Its  anterior  surface  is  arranged  in  folds,  in  the  depressions 
of  which  the  ciliary  processes  lie.  From  these  processes  the  liga- 
ment passes  to  the  capsule  of  the  lens.  Its  function  is  to  assist  in 
retaining  the  lens  in  position. 

Chemistry  of  the  Eye. —  Cornea. — An  analysis  of  the  cornea 
shows  that  it  consists  of  the  following  ingredients :  Water,  75.8 
per  cent. ;  collagen,  20.4  per  cent. ;  other  organic  matter,  2.8  per 
cent. ;  and  ash,  1  per  cent. 

Retina. — This  tunic  has  been  analyzed  in  geese,  with  the  fol- 
lowing result : 


FIG.  332.— Crystalline  lens :  A,  longi- 
tudinal fibers ;  a,  anterior  capsule ;  6, 
anterior  epithelium;  c,  lens-fibers.  B, 
posterior  surface  view  of  anterior  epithe- 
lium (Leroy). 


556 


THE  NERVOUS  SYSTEM. 


Water 86  to     89  per  cent. 

Solids 14  "11       " 

Proteids  (globulin  coagulating  at  50  per  cent., 

albumin,  and  mucin) 4  6 

Gelatin 13  17 

Cholesterin 0.3  0.8 

Lecithin 1  2.9 

Fat 0.05          0.5 

Salts 0.7  1.2 

Retinal  Pigments. — The  black  retinal  pigment  is  fuscin,  and  is 

Practically  identical  with  the  pigment  of  the  iris  and  choroid. 
t  belongs  to  the  group  of  pigments  called  melanins,  and  differs 
but  little  if  at  all  from  the  coloring-matter  in  the  skin  of  negroes 
and   in  melanotic  tumors.     Fuscin  contains  iron,  but  it  is  still 
undecided  whether  it  is  derived  from  hemoglobin  or  not. 

Rhodopsin  or  visual  purple  is  the  pigment  in  the  outer  portion 
of  the  retinal  rods ;  it  bleaches  out  when  exposed  to  light,  and  is 
supposed  to  be  derived  from  fuscin.  The  chemistry  of  this  pig- 
ment is  undetermined.  Of  the  yellow  pigment  characteristic  of 
the  macula  lutea  but  little  is  known. 

Aqueous  Humor. — This  fluid  is  lymph.  Its  analysis  is  as 
follows : 

Water 98.687  per  cent. 

Solids 1.313  " 

{Fibrinogen          ^ 

Serum-albumin   L 0.122  " 
Serum-globulin  J 

Extractives 0.421  " 

Inorganic  salts 0.77  " 

Sodium  chlorid      0.689  " 

Vitreous  Humor. — From  the  hyaloid  membrane  gelatin  may  be 
obtained,  also  mucoid  and  a  small  amount  of  proteid. 

Crystalline  Lens. — The  following  is  the  analysis  of  the  lens  : 

Water ' 63.5    percent. 


Solids 
Proteids   . 
Lecithin  . 
Cholesterin 
Fats  .    .    . 
Salts 


36.5 
34.93 
0.23 
0.22 
0.29 
0.82 


The  proteid  is  a  globulin  called  crystallin — or,  rather,  a-crys- 
tallin  and  ^-crystallin ;  there  is  also  a  small  amount  of  albumin 
in  the  lens.  In  the  "  proteids  "  is  a  considerable  amount — about 
48  per  cent. — of  an  albuminoid  substance,  insoluble  in  water  and 
saline  solutions. 

Ocular  Muscles  (Figs.  333,  334). — The  muscles  which  move  the 
eyeball  are  6  in  number :  (1)  Superior  rectus ;  (2)  inferior  rectus ; 
internal   rectus ;    (4)  external  rectus ;    (5)  superior  oblique ; 
inferior  oblique. 


SENSE  OF  SIGHT. 


557 


Superior  Rectus. — Its  origin  is  from  the  upper  margin  of  the 
optic  foramen  and  the  fibrous  sheath  of  the  optic  nerve ;  its  inser- 
tion is  into  the  sclerotic,  about  0.6  cm.  from  the  margin  of  the 
cornea.  Nerve-supply  is  from  the  oculomotorius. 

Inferior  Rectus.— Its  origin  is,  in  common  with  the  internal 
rectus,  from  the  ligament  or  tendon  ofZinn;  this  is  an  aponeurosis 
which  is  attached  around  the  circumference  of  the  optic  foramen, 
with  the  exception  of  the  upper  and  lower  parts ;  its  insertion  is 


FIG.  333. — Ocular  muscles  viewed  after  removal  of  lateral  wall  of  orbit :  a,  eye- 
ball; 6,  optic  nerve;  c, c',  eyelids;  d,  maxillary  sinus;  e,  pterygoid  plate;  /,  fora- 
men rotundum ;  g,  roof  of  orbit ;  h,  frontal  sinus ;  i,  supra-orbital  nerve ;  k,  septum 
orbitale  ;  1,  levator  palpebrse  superioris;  2,  3,  superior  and  inferior  recti ;  4,4',  por- 
tions of  the  cut  external  rectus ;  5,  internal  rectus ;  6,  inferior  oblique ;  7,  insertion 
of  superior  oblique;  8,  annular  ligament  of  tendon  of  Zinn  (Testut). 

into  the  sclerotic,  about  0.6  cm.  from  the  cornea.  Nerve-supply  is 
from  the  oculomotorius. 

Internal  Rectus. — Its  origin  is  from  the  ligament  of  Zinn  ;  its 
insertion,  into  the  sclerotic,  about  0.6  cm.  from  the  cornea.  Nerve- 
supply  is  from  the  oculomotorius. 

External  Rectus. — Its  origin  is  by  two  heads,  the  upper  from 
the  outer  margin  of  the  optic  foramen,  and  the  lower  from  the 
ligament  of  Zinn  and  a  bony  process  at  the  lower  margin  of  the 
sphenoidal  fissure  ;  its  insertion  is  into  the  sclerotic,  about  0.6  cm. 


558 


THE  NERVOUS  SYSTEM. 


from  the  margin  of  the  cornea.     Nerve-supply  is  from  the  ab- 
ducens. 

Superior  Oblique. — Its  origin  is  from  above  the  inner  margin 
of  the  optic  foramen ;  thence  it  passes  to  the  inner  angle  of  the 
orbit,  where  it  terminates  in  a  rounded  tendon  which  plays  through 
a  fibrocartilaginous  ring.  It  passes  under  the  superior  rectus,  and 


FIG.  334. — Ocular  muscles  of  right  side,  viewed  from  above,  after  removal  of  roof 
of  orbit:  A,  frontal  bone  ;  B,  section  of  great  wing  of  sphenoid  ;  C,  section  of  malar 
bone ;  D,  anterior  clinoid  process ;  E,  optic  nerve ;  1,  superior  rectus ;  2,  superior 
oblique  muscle  with  its  pulley  (2')  and  its  insertion  into  the  eyeball  (2") ;  3,  inter- 
nal rectus ;  4,  external  rectus ;  5,  common  origin  (ligament  of  Zinn)  of  muscles ; 
6,  cut  tendon  of  levator  palpebrse;  7,  7',  7",  palpebral  expansion  of  same;  8,  inser- 
tion of  inferior  oblique ;  9,  intra-orbital  cushion  of  fat ;  10,  orbicularis  palpebrarum 
(Testut). 


its  insertion  is  into  the  sclerotic,  between  the  superior  rectus  and 
the  external  rectus,  midway  between  the  cornea  and  the  optic 
nerve.  Nerve-supply  is  from  the  trochlearis. 

Inferior  Oblique. — Its  origin  is  from  the  orbital  plate  of  the 
superior  maxilla,  external  to  the  lacrimal  groove  for  the  nasal 
duct ;  its  insertion  is  into  the  sclerotic,  between  the  superior  rectus 


SENSE  OF  SIGHT. 


559 


and  the   external    rectus,   behind   the   insertion   of  the  superior 
oblique.     Nerve-supply  is  from  the  oculomotorius. 

Functions  of  the  Ocular  Muscles  (Figs.  335,  336). — The  supe- 
rior rectus  turns  the  eye  upward  and  inward ;  when  the  eye  is 
turned  directly  upward  this  is  brought  about  by  the  conjoint 


4       4 


6  6 

FIG.  335. — Movements  of  the  eyeballs:  1,  inferior  oblique;  2,  superior  rectus;  3, 
external  rectus ;  4,  internal  rectus ;  5,  superior  oblique ;  6,  inferior  rectus. 

action  of  the  superior  rectus  and  the  inferior  oblique.  The  in- 
ferior rectus  turns  the  eye  downward  and  inward ;  when  the  eye 
is  turned  directly  downward,  this  is  effected  by  the  conjoint  action 
of  the  inferior  rectus  and  the  superior  oblique.  The  internal 


FIG.  336. — Horizontal  section  of  left  eye.  Arrows  show  direction  of  pull  of  the 
muscles.  The  axis  of  rotation  of  the  external  and  internal  recti  would  pass  through 
the  intersection  of  a  and  £  at  right  angles  to  the  plane  of  the  paper  (Stewart). 

rectus  turns  the  eye  inward  ;  the  external  rectus  turns  it  outward. 
The  superior  oblique  rotates  the  eye  outward  on  its  anteroposterior 
axis,  and  corrects  the  inward  deviation  of  the  inferior  rectus.  The 
inferior  oblique  rotates  the  eyeball  outward  on  its  anteroposterior 
axis,  and  corrects  the  inward  deviation  of  the  superior  rectus. 


560  THE  NERVOUS  SYSTEM. 

Physiology  of  Vision.— The  eye  has  very  aptly  been  compared 
to  a  photographic  camera,  the  transparent  structure,  through  which 
pass  the  rays  of  light,  representing  the  lenses,  and  the  retina 
representing  the  sensitive  plate  on  which  the  image  is  received, 
while  the  pigmented  choroid  coat  is  the  representative  of  the 
lampblack  with  which  the  photographer  darkens  the  interior  of 
the  camera-box  to  prevent  any  reflected  light  striking  the  plate 
and  interfering  with  the  sharpness  of  the  picture.  In  the  camera, 
in  order  to  bring  to  a  focus  upon  the  plate  the  rays  of  light  coming 
from  objects  at  different  distances,  the  photographer  uses  a  focus- 
sing screw,  by  which  the  lens  may  be  moved  nearer  to  or  farther 
from  the  object  he  wishes  to  photograph ;  and  in  order  that  clear 
images  may  be  obtained  by  the  eye  it  is  necessary  to  accomplish 
the  same  result,  for  when  the  eye  is  focussed  for  near  objects,  those 
at  a  distance  are  blurred,  and  vice  versd.^  This  fact  may  readily 
be  demonstrated  by  looking  through  a  piece  of  mosquito-netting 
at  the  windows  of  a  house  on  the  opposite  side  of  a  street.  When 


FIG.  337.— Principal  focus  of  a  lens.  The  parallel  rays,  a,  6,  c,  d,  are  refracted 
by  the  lens  so  as  to  unite  at  the  point  F  on  the  axis  P;  the  ray  P  undergoes  no 
refraction.  F  is  the  principal  focus. 

the  threads  of  the  net  can  be  seen  distinctly,  the  bars  of  the  window 
will  be  indistinct,  and  when  the  bars  of  the  window  are  clear  and 
distinct,  then  the  threads  are  blurred.  In  the  optical  apparatus 
of  the  eye  there  is  no  provision  for  altering  the  position  of  the 
lenses,  but  there  is  one  which  answers  the  same  purpose,  and  which 
is  called  accommodation.  In  connection  with  every  camera  there 
is  an  arrangement  of  openings  or  diaphragms  by  which  a  greater  or 
lesser  amount  of  light  may  be  admitted,  according  to  circum- 
stances. In  the  eye  the  iris  serves  a  similar  purpose.  In  many 
cameras  it  is  necessary  to  have  a  number  of  such  diaphragms,  each 
having  an  opening  of  a  different  size,  but  some  are  provided  with  a 
single  one,  the  size  of  whose  opening  can  be  altered ;  this  is  called 
an  "  iris  diaphragm,"  and  is  a  rude  contrivance  compared  with  the 
natural  iris  from  which  it  derives  its  name,  and  which  by  means 
of  its  muscular  fibers  can  alter  in  a  moment  the  size  of  the  pupil. 
Rays  of  light  coming  from  an  object,  in  order  to  produce  a 
distinct  image  of  that  object,  must  be  brought  to  a  focus  upon  the 
retina  (Fig.  337).  If  the  media  through  which  the  light  from  an 


SENSE  OF  SIGHT.  561 

object  passes  to  reach  the  retina  were  all  of  the  same  density  as  the 
air,  and  were  also  plane  surfaces,  an  impression  would  be  produced, 
but  there  would  be  no  distinct  image.  Actually,  before  such  rays 
do  reach  the  retina  they  pass  through  certain  media  which,  by 
reason  of  both  density  and  shape,  refract  them  and  bring  them  to 
a  focus,  thus  producing  a  sharp  and  distinct  image  of  the  object 
looked  at.  These  media  are  the  cornea  covered  with  a  layer  of 
tears,  aqueous  humor,  crystalline  lens  with  its  anterior  and  poste- 
rior capsule,  and  vitreous  humor,  seven  in  all.  The  amount  of 
refraction  is  determined  by  the  radius  of  curvature  of  the  surface 
through  which  the  rays  pass,  the  refraction  being  greater  as  the 
radius  becomes  smaller,  and  by  the  difference  between  the  refrac- 
tive indices  of  the  media,  refraction  increasing  as  the  difference 
increases.  The  radii  of  curvature  are  as  follows  : 

When  accommodated  for 


Far  vision.  Near  vision. 

Cornea 8mm.  8     mm. 

Anterior  surface  of  lens 10    "  6        " 

Posterior       "      "      " 6    "  5.5     " 

The  refractive  indices  of  the  various  media  through  which  the 
light  passes  are  as  follows  : 


Tears l.J 

Cornea 1.337 

Aqueous  humor 1.3365 

Vitreous       " 1.3365 

Lens  (mean  for  all  layers) 1.437 

The  refractive  index  of  air  is  1.000,  and  of  water  1.335.  From 
this  table  it  will  be  seen  that  the  tears,  cornea,  and  aqueous  humor 
have  practically  the  same  indices  of  refraction,  and  we  may  there- 
fore regard  the  media  through  which  light  passes  to  reach  the 
retina  as  three  in  number:  1,  tears,  cornea,  and  aqueous  humor, 
with  a  refractive  index  of  1.33;  2,  crystalline  lens,  with  a  re- 
fractive index  of  1.43;  and  3,  vitreous  humor,  with  a  refractive 
index  of  1.33. 

The  following  table  gives  the  distances  between  the  various 
points  mentioned  therein : 

When  accommodated  for 


Far  vision.      Near  vision. 

Anterior  surface  of  cornea  and  anterior  surface  of  lens  .  .    3.6  mm.        3.2  mm. 

"  "  "  "     posterior      "          "        .  .    7.2    "  7.2    " 

«  "  lens          "  "  "          "        .  .    3.6    " 

Posterior      "  "     retina  "       .  .  14.6    "  14.6     " 

The  anteroposterior  diameter  of  an  em  me  tropic  eye  along  the 
axis  is  21.8  mm. 

36 


562 


THE  NERVOUS  SYSTEM. 


The  data  here  given  are  known  as  optical  constants,  and  the 
figures  may  be  regarded  as  averages,  individual  eyes  differing,  as 
would  naturally  be  expected. 

Reduced  Eye  (Fig.  338). — For  purposes  of  calculation,  an 
imaginary  eye,  the  reduced  or  schematic  eye,  has  been  proposed, 


FIG.  338.— The  reduced  eye:  S,  the  single  spherical  refracting  surface,  1.8  mm. 
behind  the  anterior  surface  of  the  cornea;  N,  the  nodal  point,  5  mm.  behind  S  ;  F, 
the  principal  focus  (on  the  retina),  20  mm.  behind  S.  The  cornea  and  lens  are  put 
in  in  dotted  lines  in  the  position  which  they  occupy  in  the  normal  eye  (Stewart). 

whose  refractive  medium  is  a  single  one,  representing,  approxi- 
mately enough  for  practical  purposes,  the  natural  eye.  This  eye 
has  the  following  characteristics  (Listing) : 


From  anterior  surface  of  cornea  to  the  principal  point 
From  nodal  point  to  the  posterior  surface  of  lens 
Posterior  principal  focus  behind  cornea  .    .    .    . 
Anterior  principal  focus  in  front  of  cornea     .    . 
Kadius  of  curvature  of  single  refracting  surface 
Index  of  refraction  of  single  refractive  medium 


.    2.3448  mm. 
.    0.4764 

.  22.8237 

.  12.8326 

.    5.1248 

1.33 


The  optical  and  visual  axes  may  be  regarded  as  identical,  and 
as  represented  by  a  line  which  passes  through  the  centers  of  cur- 
vature of  the  cornea  and  lens  directly  backward  until  it  terminates 


FIG.  339. — Diagram  of  the  formation  of  a  retinal  image  (after  Foster). 

in  the  fovea  centralis.     Rays  of  light  falling  upon  the  cornea  are 
refracted  and  made  convergent,  and  this  effect  is  increased  by  the 


SENSE  OF  SIGHT.  563 

lens  and  vitreous,  so  that  when  the  rays  reach  the  retina  they  are 
brought  to  a  focus.  This  is  shown  in  Fig.  339,  where  the  arrow 
XY  is  projected  upon  the  retina,  forming  the  inverted  image  YX. 

The  angle  xnY  is  the  visual  or  optical  angle,  also  called  the 
angle  of  vision,  and  determines  the  size  of  the  image  upon  the  retina. 

If  an  object  subtends  an  angle  less  than  50  seconds,  it  cannot 
be  seen,  because  the  size  of  the  image  upon  the  retina  would  be 
less  than  3.65  p. ;  the  distance  between  the  centers  of  two  adjacent 
cones  being  about  4  //,  each  cone  having  a  diameter  of  about  3  fi. 

Retinal  Images  are  Inverted. — By  reference  to  Fig.  339  it 
will  be  seen  that  the  retinal  image  is  inverted  •  the  question  nat- 
urally arises,  therefore,  Why  are  not  the  objects  which  form  these 
images  seen  in  an  inverted  position  ?  The  answer  to  this  question 
is  that  objects  are  "seen"  by  the  brain,  and  not  by  the  retina; 
that  certain  impressions  are  produced  by  the  light  upon  the  retina ; 
and  that  these  impressions  are  transmitted  to  the  brain  by  the 
optic  nerve,  and  are  there  interpreted  in  the  form  of  what  is 

A 


FIG.  340. — Diagram  illustrating  the  projection  of  a  shadow  on  the  retina. 

called  "  sight."  The  brain  has  by  long  experience  come  to  asso- 
ciate the  top  of  an  object  with  the  image  which  the  top  of  the 
object  produces  on  the  retina,  so  that  although  the  upper  end 
of  an  object — as  the  point  of  an  arrow,  for  instance — makes  its 
image  below,  and  the  lower  end — or,  in  the  supposed  instance,  the 
head  of  the  arrow — forms  its  image  above,  the  brain  sees  the 
arrow  with  its  point  up  and  the  head  down.  Light  which  reaches 
the  retina  is  always  referred  by  the  brain  to  an  object  situated  on 
the  opposite  side.  Thus  light  which  reaches  the  right  side  of  the 
retina  comes  from  the  left,  and  that  which  reaches  its  left  side 
comes  from  the  right. 

It  is  a  curious  fact  that  when  an  upright  object  makes  an 
upright  image  on  the  retina,  the  brain  inverts  the  object,  so  that 
it  is  seen  in  an  inverted  position.  This  is  illustrated  in  Fig.  340, 
for  which  and  for  the  recital  of  the  fact  we  are  indebted  to  the 
American  Text-book  of  Physiology.  If  a  card  with  a  small  pin- 
hole  in  it  is  placed  in  front  of  a  source  of  light  and  about  three  or 


564  THE  NERVOUS  SYSTEM. 

.4 

four  centimeters  from  the  eye,  and  the  head  of  a  pin  is  held  as 
close  as  possible  to  the  cornea,  the  pinhole  becomes  a  source  of 
light,  and  the  shadow  of  the  pin,  not  the  image — for  the  pin  is  too 
near  the  eye  to  form  an  image — falls  on  the  retina.  This  shadow 
is  an  upright  one,  and  yet  the  pinhead  appears  inverted,  for  the 
reason  that  the  brain  has  become  accustomed  to  interpret  all  im- 
pressions made  upon  the  retina  as  corresponding  to  objects  in 
the  opposite  portion  of  the  field  of  vision.  In  the  illustration, 
AB  is  the  card  with  the  pinhole,  P  the  pin,  and  p'  its  upright 
shadow  on  the  retina. 

Accommodation  (Figs.  341,  342). — The  eye  possesses  the  capa- 
bility of  adjusting  itself  to  seeing  objects  at  varying  distances ; 
this  is  accommodation.  If  the  entire  optical  apparatus  of  the  eye 
was  rigid  and  immovable,  it  would  be  necessary,  in  order  to  obtain 


FIG.  341. — Anterior  quadrant  of  a  horizontal  section  of  the  eyeball,  cornea  and 
lens  cut  in  the  middle  of  their  vertical  diameter:  a,  substantia  propria  of  the 
cornea;  6,  Bowman's  membrane;  c,  anterior  corneal  epithelium;  d,  Descemet's 
membrane;  e,  its  epithelium;  /,  conjunctiva;  g,  sclera  ;  h,  iris;  i,  sphincter  muscle 
of  the  iris  ;  j,  pectinate  ligament  of  the  iris  with  the  adjacent  fenestrated  tissue  ; 
k,  canal  of  Schlemm  ;  I,  longitudinal,  m,  circular  fibers  of  the  ciliary  muscle ;  n,  cil- 
iary process ;  o,  ciliary  portion  of  the  retina ;  q,  canal  of  Petit,  with  the  zonule  of 
Zinn  (Z)  in  front  of  it,  the  posterior  leaflet  of  the  hyaloid  membrane  (P)  behind 
it ;  r,  anterior,  s,  posterior,  capsule  of  the  lens ;  <,  choroid ;  n,  perichoroidal  space ; 
T,  pigment  epithelium  of  the  iris;  x,  margin  (equator)  of  the  lens.  (Landois). 

a  clear  image  of  an  object,  either  for  the  individual  to  approach  or 
to  recede  from  the  object,  or  to  cause  the  object  to  do  the  same  with 
reference  to  him,  for  only  parallel  rays,  namely,  rays  coming  from 
objects  at  a  distance  of  two  to  three  meters  or  more,  are  brought  to 
a  focus  in  the  normal  eye  unless  some  change  is  brought  about  in 


SENSE  OF  SIGHT. 


565 


the  refractive  media.  If  an  object  is  within  that  distance,  the  rays 
of  light  coming  from  it  are  brought  to  a  focus  by  altering  the  shape 
of  the  crystalline  lens ;  this  is  positive  accommodation. 

As  already  stated,  the  optical  apparatus  of  the  eye  is  in  a  state 
of  rest  when  it  is  looking  at  objects  more  than  two  to  three  meters 


CS1 


FIG.  342. — Diagrammatic  representation  of  accommodation  for  near  and  far  ob- 
jects. On  the  right  the  condition  during  positive  accommodation  is  shown,  on  the 
left  the  condition  during  rest  (negative  accommodation).  On  both  sides  one-half  of 
the  contour  of  the  lens  is  drawn  as  a  continuous  line,  the  other  half  as  a  dotted  line. 
The  letters  appearing  twice— on  both  the  right  and  left  sides— have  the  same  sig- 
nificance ;  those  on  the  right  side  are  primed  A,  left,  B,  right  half  of  the  lens;  C, 
cornea ;  <S',  sclera ;  C.8.,  canal  of  Schlemm ;  V.K.,  anterior  chamber  ;  J,  iris ;  P, 
pupillary  margin  ;  V,  anterior,  H,  posterior  surface  of  the  lens ;  B,  equator  of  the 
lens ;  F,  edge  of  the  ciliary  processes ;  a  and  6,  interval  between  them.  The  line 
Z-X shows  the  thickness  of  the  lens  in  the  act  of  accommodation  for  a  near  object; 
Z-F,  the  thickness  of  the  lens  when  the  eye  is  at  rest.  (Landois.) 


distant,  this  is  negative  accommodation  ;  thus  to  see  the  stars,  although 
millions  of  kilometers  distant,  no  effort  is  required ;  but  if  it  is  de- 
sired to  see  objects  less  than  two  or  three  meters  away,  there  is  a 
change  in  the  refractive  media  until  objects  are  brought  to  a  point 
so  close  to  the  eye  that  no  amount  of  effort  will  enable  them  to  be 
seen.  The  point  at  which  objects  cease  to  be  seen  distinctly  is  called 
the  near  point,  and  it  is,  for  a  normal  or  emmetropic  eye  about  12  cm., 
although  it  is  not  the  same  in  all  persons. 

The  positive  accommodation  of  the  eye  is  brought  about  espe- 
cially by  the  change  in  the  shape  of  the  crystalline  lens ;  thus  in 
looking  at  near  objects  the  lens  becomes  more  convex.  This  is 
accomplished  in  the  following  manner*:  The  lens  is  a  very  elastic 
structure,  enclosed  in  a  capsule  to  which  the  zonule  of  Zinn  is  at- 
tached, and  the  tension  of  this  structure  is  such  as  to  pull  upon  the 
anterior  portion  of  the  capsule  and  flatten  it,  at  the  same  time 
flattening  the  anterior  surface  of  the  contained  lens.  This  is 
the  condition  when  the  eye  is  looking  at  distant  objects  or  is  in  a 
state  of  accommodative  rest.  But  when  a  near  object  is  to  be 
looked  at,  the  radiating  fibers  of  the  ciliary  muscle  contract,  and 
as  its  fixed  point  is  at  the  junction  of  the  cornea  and  sclerotic,  this 
contraction  draws  the  ciliary  processes  forward  and  relaxes  the 


566  THE  NERVOUS  SYSTEM. 

zonule,  thus  removing  the  influence  which  tends  to  flatten  the  lens, 
and  pe  mits  the  latter,  by  its  elasticity,  to  become  more  convex. 
The  nervous  supply  for  this  act  is  furnished  to  the  ciliary  muscle 
by  the  motor  oculi  through  the  ciliary  ganglion  and  nerves.  At 
the  same  time  that  this  muscular  action  is  taking  place  the  pupil 
becomes  smaller  and  the  eyes  converge. 


FIG.  343.— Reflected  images  of  a  candle-flame  as  seen  in  the  pupil  of  an  eye  at  rest 
and  accommodated  for  near  objects  (Williams). 


This  is  the  usual  explanation  of  accommodation,  and  may  be 
demonstrated  in  the  following  manner:  If  in  a  dark  room  a  candle- 
flame  is  held  about  50  cm.  distant  from  and  at  the  side  of  the  eye 
of  a  person  who  is  looking  at  a  distant  object,  an  observer  standing 


FIG.  344. — Diagram  explaining  the  change  in  the  position  of  the  image  reflected 
from  the  anterior  surface  of  the  crystalline  lens  (Williams,  after  Bonders). 

at  his  other  side  will  see  reflected  from  the  observed  eye  three  images 
of  the  flame  (Fig.  343) — (a)  the  brightest  and  most  distinct  being 
an  erect  image,  which  is  formed  by  the  anterior  surface  of  the 


SENSE  OF  SIGHT.  567 

cornea.  Besides  this  image  there  is  a  second  image  (6),  which 
is  also  erect,  but  which  is  less  distinct  and  larger ;  this  image 
is  formed  at  the  anterior  surface  of  the  lens.  A  third  image  (c) 
is  also  seen,  which  is  inverted  and  also  indistinct ;  this  image  is 
formed  by  the  posterior  surface  of  the  lens,  which,  being  concave 
forward,  acts  like  a  concave  mirror  and  inverts  the  image.  These 
are  called  Purkinje-Sanson  images.  If  the  person  then  looks  as  if 
at  a  near  object,  the  second  image  becomes  brighter  and  smaller,  and 
at  the  same  time  approaches  the  first,  while  the  first  image  under- 
goes no  change,  and  the  third  a  change  so  slight  as  not  to  be  per- 
ceptible (Fig.  343).  This  proves  that  in  accommodating  the  eye 
for  near  objects  the  principal  change  which  takes  place  is  an  in- 
crease in  the  convexity  of  the  anterior  surface  of  the  crystalline 
lens.  There  is  also  a  slight  increase  in  the  convexity  of  the 
posterior  surface,  while  the  cornea  remains  unchanged.  In  Fig. 
344  the  course  taken  by  the  rays  of  light  is  delineated.  The  eye 
whose  accommodation  is  under  investigation. is  directed  to  A,  while 


FIG.  345. — Phakoscope  of  Helmholtz:  at  B  B'  are  two  prisms,  by  which  the  light 
of  a  candle  is  concentrated  on  the  eye  of  the  person  experimented  with ;  A  is  the 
aperture  for  the  eye  of  the  observer.  The  observer  notices  three  double  images 
reflected  from  the  eye  under  examination  when  the  eye  is  fixed  upon  a  distant 
object ;  the  position  of  the  images  having  been  noticed,  the  eye  is  then  made  to  focus 
a  near  object,  such  as  a  reed  pushed  up  :  the  images  from  the  anterior  surfaces  of  the 
lens  will  be  observed  to  move  toward  each  other,  in  consequence  of  the  lens  becom- 
ing more  convex. 

the  candle-flame  and  the  observer's  eye  are  on  opposite  sides.  The 
images  of  the  candle-flame  will  appear  along  the  line  II',  on  the 
dark  background  of  the  pupil.  The  image  produced  by  reflection 
from  the  cornea  is  seen  at  the  termination  of  the  dotted  line  a  ; 
that  from  the  posterior  surface  of  the  lens,  at  the  termination  of 
c  ;  and  that  from  the  anterior  surface  of  the  lens  when  the  eye  is 
in  a  state  of  accommodative  rest — i.  e.3  looking  at  distant  objects — 


568 


THE  NERVOUS  SYSTEM. 


at  the  termination  of  b  ;  when  focussed  for  near  objects  and  the 
anterior  surface  of  the  lens  moves  forward,  the  image  is  seen  at 
the  termination  of  b'—i.  e.,  nearer  the  corneal  image ;  it  is  also 
smaller  and  brighter.  The  change  in  the  convexity  of  the  anterior 

surface  of  the  lens  may  also 
be  shown  by  looking  at  the 
eye  from  the  side,  as  in  ac- 
commodation the  iris  may  be 
seen  to  move  forward,  being 
pushed  in  that  direction  by 
the  anterior  surface  of  the 
lens,  with  which  it  is  in  con- 
tact. 

Phakoscope  of  Helmholtz 
(Fig.  345).— This  apparatus 
was  devised  by  Helmholtz 
to  demonstrate  the  changes 
which  have  just  been  de- 
scribed, and  which  were  ad- 
vanced by  him  to  explain 
accommodation. 

The  eye  of  the  person 
whose  accommodation  is  to 

FIG.  346.— Purkinje-Sanson  images:  A,  in  ,       ofnrlWl  '  i«   nlippfl    at    C 

the  absence  of   accommodation ;  B.    during  be   Studied  ^18   placed    at    O. 

accommodation  for  a  near  object.    The  upper  For   near  V1S1O11   the   needle 

pair  of  circles  enclose  the  images,  as  seen  when  ,    j)  •     .      L     ]c.r.]fftf\  „+    «nrl 

the  light  falls  on  the  eye  through  a  double  slit  «  D  .1S  tO  -DC  ^OOked  at,  and 

or  a  pair  of  prisms;  the  lower  pair  show  the  lor   distant  Vision   some  OD- 

images  seen  when  the  slit  is  single  and  tri-  |ect   jn   the   game   direction, 

angular  in  shape  (Stewart).  *  ,    T>         i     -r>/  ^ 

At  B  and  E'  there  are  two 

prisms,  in  front  of  which  a  candle-flame  is  placed.  The  eye  of 
the  observer  at  A  sees  two  sets  of  the  three  reflected  images,  each 
image  being  a  square  spot  of  light ;  those  reflected  from  the  ante- 
rior surface  of  the  lens  approach  those  reflected  from  the  cornea,  as 
already  explained,  and  also  approach  each  other  (Fig.  346). 

Tscherning's  Theory  of  Accommodation. — This  authority  ex- 
plains positive  accommodation  by  supposing  that  by  the  contrac- 
tion of  the  anterior  part  of  both  the  radiating  and  circular  fibers 
of  the  ciliary  muscle  the  ciliary  processes  are  drawn  backward,  and 
that  this  pulls  the  zonule  of  Zinn  (suspensory  ligament)  backward 
and  outward.  This  increases  the  tension  of  the  ligament  and  the 
pressure  upon  the  lens,  the  external  or  softer  portion  of  which  is 
caused  to  bulge  out,  this  change  being  especially  marked  on  its 
anterior  surface.  The  contraction  of  the  posterior  portion  of  the 
ciliary  muscle  pulls  forward  the  choroid,  and  thus  makes  tense,  so 
to  speak,  the  vitreous,  preventing  it  from  yielding  when  the  lens 
is  pressed  against  it  by  the  anterior  portion ;  thus  the  pressure  of 


SENSE  OF  SIGHT. 


569 


the   anterior   portion   of  the    muscle    causes    the  increased  con- 
vexity of  the  lens,  and  not  its  displacement  backward. 

Schoen's  Theory  of  Accommodation  (Fig. 
347). — This  writer  explains  the  increased 
convexity  of  the  lens  by  assuming  that  the 
contraction  of  the  ciliary  muscle  produces  the 
same  effect  on  the  lens  as  is  produced  upon  a 
rubber  ball  when  held  in  both  hands  and  com- 
pressed by  the  fingers.  The  theories  of  Tscher- 
ning  and  Schoen  presupposes  a  stretching  of 
the  zonule  of  Zinn,  while  that  of  Helmholtz  is 
based  on  its  relaxation.  Recent  observations  of 
Hess  seem  to  demonstrate  that  the  change  in 
this  structure  is  one  of  relaxation  rather  than 
increased  tension,  so  that  at  the  present  time 
the  theory  of  Helmholtz  may  be  accepted  as 
the  true  explanation  of  accommodation. 

Range  of  Accommodation. — The  point 
nearest  to  the  eye  to  which  objects  can  be 
brought  and  be  seen  distinctly  is  the  near- 
point  ;  while  the  point  farthest  from  the  eye 
at  which  distinct  vision  exists  is  the  far-point 


FIG.  347.— To  illus- 
trate Schoen' s  theory 
of  accommodation. 


intervening  space  is  the  range  of  accommodation. 


the  length  of  the 


FIG.  348.— Scheiner's  experiment.  In  the  upper  figure  the  eye  is  focussed  for  a 
point  farther  away  than  the  needle ;  in  the  lower,  for  a  nearer  point.  The  continuous 
lines  represent  rays  from  the  needle,  the  interrupted  lines  rays  from  the  point  in 
focus. 

Near-point. — This  is  also  called  punctum  proximum,  and  is  ex- 
pressed by  p.p.  It  varies  in  different  individuals,  but  for  a  normal 
adult  eye  is  about  12  cm.  Objects  brought  nearer  to  the  eye  than 
this  cannot  be  seen  with  distinctness,  for  the  refractive  media 
cannot  bring  the  image  of  such  objects  to  a  focus  upon  the  retina. 
The  near-point  for  any  given  eye  may  be  determined  by  Scheiner's 


570  THE  NERVOUS  SYSTEM. 

experiment  (Fig.  348).  In  a  "card  two  pinholes  are  made  whose 
distance  from  each  other  must  not  exceed  the  diameter  of  the 
pupil,  about  2  mm.  Through  these  holes,  with  the  card  held  close 
to  the  eye,  a  needle  is  looked  at.  It  will  appear  single ;  if  the 
needle  is  brought  near  to  the  eye,  a  point  will  be  reached  at  which 
it  appears  double,  or  it  may  be  blurred ;  this  is  the  near-point  for 
the  eye  in  question. 

Far-point. — This  is  also  known  as  punctum  remotum,  or  p.  r. 
It  is  the  farthest  point  at  which  objects  can  be  seen  distinctly  by  a 
normal  eye,  and  is  infinitely  distant ;  so  that  the  range  of  accom- 
modation in  the  normal  eye  is  from  about  12  cm.  to  infinity.  Asj 
a  matter  of  fact,  rays  of  light  which  reach  the  retina  from  any 
object  not  more  than  two  meters  distant  from  the  eye  are  practi- 
cally parallel,  so  that  in  looking  at  objects  at  any  distance  greater 
than  this  there  is  no  change  in  the  accommodative  apparatus — 
i.  e.j  the  eye  is  in  a  state  of  accommodative  rest ;  while  as  objects 
are  brought  nearer  than  two  meters  there  is  necessitated  an  increase 
in  the  convexity  of  the  lens  in  order  that. they  may  be  seen  dis- 
tinctly until  the  near-point  is  reached,  within  which  their  images 
become  blurred  by  reason  of  the  fact  that  the  lens  has  reached 
the  limit  to  which  its  convexity  can  be  increased. 

Convergence  of  the  Eyes  during  Accommodation. — If,  as  an  object 
is  brought  nearer  to  the  eyes  of  an  observer,  his  eyes  are  inspected 
by  another,  it  will  be  seen  that,  as  the  accommodative  apparatus  is 
brought  into  action  to  focus  the  image  on  the  retina,  the  eyes  are 
at  the  same  time  turned  inward — i.  e.,  made  to  converge.  When 
it  is  remembered  that  in  order  to  produce  distinct  vision  the  image 
must  be  formed  in  the  fovea  centralis,  it  will  be  seen  that  as  the 
object  is  brought  nearer  to  the  eyes  each  eye  must  be  turned  in- 
ward, otherwise  the  image  would  not  fall  upon  the  fovea. 

Contraction  of  the  Pupil  during  Accommodation.— When  a  dis- 
tant object  is  observed,  the  pupil  is  relatively  large ;  but  when  the 
eye  is  accommodated  for  near  objects,  the  pupil  becomes  smaller. 
By  this  contraction  of  the  iris  the  very  divergent  rays  which  come 
from  the  object,  and  which,  by  reason  of  their  extreme  divergence, 
would  not  be  brought  to  a  focus  on  the  retina,  are  excluded,  and 
thus  a  sharpness  of  the  image  is  secured  which  would  not  be 
the  case  if  the  pupil  was  large  enough  to  admit  these  rays. 

Defects  in  the  Visual  Apparatus. — Emmetropia  (Fig.  349,  A). — 
The  emmetropic  or  normal  eye  is  one  in  which  parallel  rays  are 
brought  to  a  focus  upon  the  retina  when  the  eye  is  in  a  state  of 
accommodative  rest.  In  such  an  eye  the  near-point  is  about 
12  cm.  distant  from  the  eye,  the  far-point  at  infinity,  and  from 
about  two  meters  distant  to  an  infinite  distance  objects  can 
be  distinctly  seen  without  any  change  in  the  accommodative 
apparatus. 


SENSE  OF  SIGHT. 


571 


Ametropia. — Whenever  the  permanent  condition  of  an  eye  is 
not  as  described  above,  it  is  one  of  ametropia.  Of  this  condition, 
there  are  several  varieties. 

Myopia  (Fig.  349,  B). — A  myopic  eye  is  one  that  is  abnormally 
elongated,  and  some  au- 
thorities regard  an  in- 
creased convexity  -of  the 
lens  as  constituting  an 
essential  part  of  this  con- 
dition. The  retina  is  so 
far  from  the  lens  that 
parallel  rays  are  focussed 
in  front  of  it,  and,  cross- 
ing, do  not  form  distinct 
images  on  the  retina,  the 
images  being  blurred.  To 
correct  this,concave  glasses 
are  used,  which  cause  these 
rays  to  diverge  as  they  en- 
ter the  eye,  and  by  adjust- 
ing the  concavity  to  the 
amount  of  myopia,  par- 
allel rays  are  brought  to 
a  focus  on  the  retina  as 
they  are  in  the  emme- 
tropic  eye  without  glasses. 
A  myopic  eye  is  commonly 
said  to  be  a  "  near-sighted  " 
one.  The  near-point  in 
myopia  may  be  5  or  6  cm. 
from  the  eye,  while  the  far- 
point  is  comparatively  near 


FIG.  349.— Diagram  showing  the  difference 
between  (.4)  emmetropic,  (B)  myopic,  and  (C) 
hypermetropic  eyes. 


the  eye,  never  at  an  infinite  distance,  so  that  the  range  of  accom- 
modation is  extremely  limited. 

Hypermetropia  (Fig.  349,  C). — In  this  condition  the  eye  is 
shorter  than  normal,  and  the  retina  is  too  near  the  lens,  so  that 
parallel  rays  are  brought  to  a  focus  behind  the  retina  and  indis- 
tinct vision  is  produced,  as  in  the  myopic  eye.  In  the  endeavor 
to  overcome  this  defect  the  ciliary  muscle  is  liable  to  overstrain 
in  order  to  converge  the  rays  to  a  focus  upon  the  retina,  and  the 
constant  effort  is  painful  and  injurious.  The  condition  is  corrected 
by  the  use  of  convex  glasses.  The  near-point  in  the  hypermetropic 
eye  is  farther  than  in  the  normal  eye.  The  far-point  does  not 
exist,  for  objects  would  of  necessity  have  to  be  removed  to  a 
greater  distance  than  infinity,  which  is,  of  course,  impossible,  in 
order  that  the  rays  coming  from  them  might  be  converging,  and 


572  THE  NERVOUS  SYSTEM. 

thus  these  rays  be  brought  to  a  focus  upon  the  retina  when  the 
eye  was  in  a  state  of  accommodative  rest. 

Presbyopia,  which  is  sometimes  called  "  old  sight,"  sometimes 
"  long  sight,"  is  the  condition  of  the  eye  present  in  elderly  people. 
In  this  condition  it  is  difficult  to  see  near  objects,  although  the 
vision  for  those  at  a  distance  is  unaffected.  It  is  usually  attrib- 
uted to  a  lessened  elasticity  of  the  lens,  though  the  ciliary  muscle 
is  also  less  strong ;  some  writers  state  that  it  depends  on  dimi- 
nution of  the  convexity  of  the  cornea.  To  aid  in  correcting  it 
convex  glasses  are  used. 

Presbyopia  may  begin  as  early  in  life  as  the  fifteenth  year, 
although  it  commonly  does  not  until  about  the  fortieth  year. 
The  ability  to  see  objects  nearer  by  in  advanced  age,  when  pre- 
viously spectacles  were  required,  is  explained  by  an  increased 
refractive  power  which  sometimes  occurs  under  such  conditions. 


FIG.  350. — Lines  for  the  detection  of  astigmatism. 

Astigmatism  (Fig.  350). — In  this  condition  the  cornea  is  usually 
at  fault,  its  curvature  being  greater  in  one  meridian  than  in  another, 
and  consequently  the  rays  of  light  from  an  object  are  not  all 
brought  to  the  same  focus,  and  the  image,  therefore,  is  not  distinct. 
Astigmatism  is  regular  when  the  curvature  in  any  given  meridian 
is  regular  in  that  meridian,  although  the  meridian  may  differ  in 
respect  to  curvature  when  compared  with  the  one  at  right  angles 
to  it :  the  cornea  is  ellipsoidal  and  not  spherical.  Astigmatism 
is  irregular  when  in  any  given  meridian  or  meridians  the  curva- 
ture of  the  cornea  is  not  an  arc  of  a  circle  or  an  ellipse.  It 
is  irregular  astigmatism  which  causes  the  stars  to  look  as  though 
rays  projected  from  them.  For  the  correction  of  regular  astigma- 
tism glasses  are  worn  which  are  segments  of  a  cylinder — that  is, 
curved  in  but  one  direction — and  are  known  as  "  cylindrical " 
glasses.  Irregular  astigmatism  cannot  be  corrected  by  any  glasses. 
The  crystalline  lens  may  also  be  at  fault  in  astigmatism. 

Regular  astigmatism  is  detected  by  the  observation  of  con- 
centric rings  or  radiating  lines,  as  in  Fig.  350.  In  the  former 


SENSE  OF  SIGHT. 


573 


some  portions  will  be    blacker  and   more  distinct  than   others, 
while  in  the  latter  the  lines  will  present  the  same  differences. 

Spherical  Aberration  (Fig.  351). — When  rays  of  light  are 
refracted,  those  which  are  incident  near  the  edge  of  the  lens 
are  refracted  more  than  those  near  the  principal  axis,  and  will, 
therefore,  come  to  a  -focus  in  front  of  them,  and  produce  an 
indistinctness  of  the  image.  This  indefiniteness  of  focus  is 
spherical  aberration.  To  reduce  this,  a  diaphragm  is  used  in 
optical  instruments,  by  which  these  marginal  rays  are  excluded, 
or,  as  in  large  telescopic  lenses,  the  same  result  is  accomplished 
by  diminishing  the  curvature  of  the  lens  at  its  margin.  This 


FIG.  351. — Diagram  showing  the  effect  of  a  diaphragm  in  reducing  the  amount  of 

spherical  aberration. 

defect  exists  in  the  eye,  and  is  lessened  by  the  iris,  which  serves 
as  a  diaphragm  to  cut  off  the  marginal  rays,  and  also  by  the 
diminished  refractive  power  of  the  marginal  portions  of  the  lens 
as  compared  with  its  center. 

Spherical  aberration  is  more  marked  with  divergent  than  with 
parallel  rays,  and  as  rays  are  more  divergent  the  nearer  the  object 
from  which  they  come  is  to  the  eye,  this  is  corrected  by  the  greater 
contraction  of  the  iris — i.  e.,  the  greater  diminution  of  the  pupil — 
which  results  in  cutting  off  more  of  the  marginal  incident  rays. 
In  the  human  eye  spherical  aberration  is  not  an  important  defect. 

Chromatic  Aberration. — White  light  being  a  mixture  of  rays 
of  different  colors,  and  these  differing  in  refrangibility,  the  red 
being  the  least  and  the  violet  the  most  refrangible,  when  white 
light  passes  through  a  lens  it  is  broken  up  into  its  component  rays 


574  THE  NERVOUS  SYSTEM. 

— i.  e.,  undergoes  dispersion — and  the  most  refrangible  or  violet 
rays  will  be  brought  to  a  focus  nearer  the  lens  (Fig.  352)  than  the 
least  refrangible  or  red  rays,  and  between  will  be  the  various 
intermediate  colors.  When  these  rays  fall  upon  a  screen  there 
will  be  produced  a  series  of  circles  of  the  different  colors.  In 
Fig.  352  it  will  be  seen  that  if  the  screen  was  placed  at  x,  the 
outer  color  would  be  red,  and  the  inner  violet ;  while  if  it  was 


FIG.  352.— Chromatic  aberra-  FIG.  353.— Achromatic  combination 

tion  (Carhart  and  Chute).  of  lenses  (Carhart  and  Chute). 

placed  at  y,  the  colors  would  be  reversed.  This  defect  in  lenses 
is  chromatic  aberration,  and  is  overcome  by  combining  a  biconvex 
lens  of  crown  glass  with  a  planoconcave  lens  of  flint  glass 
(Fig.  353).  Inasmuch  as  images  formed  by  rays  which  have 
passed  through  such  a  combination  are  not  fringed  with  color,  the 
combination  is  achromatic. 

It  is  a  rather  curious  fact  that  the  eye  was  at  one  time  sup- 
posed to  be  free  from  this  defect,  and  its  absence  was  explained 
by  the  fact  that  the  different  media  through  which  light  passes 
to  reach  the  retina  differ  so  in  their  refracting  power  as  to  over- 
come dispersion  ;  and  it  is  said  that  it  was  this  which  led  to  the 
combination  just  described  of  the  crown  and  flint  glass  to  make 
the  achromatic  lens.  The  media  of  the  eye,  however,  do  not 
form  an  achromatic  combination,  but  the  violet  rays  are  actually 


FIG.  354. — To  show  dispersion  in  the  eye,  view  the  figure  from  a  distance  too  small 
for  accommodation.  Approach  the  eye  toward  it :  the  white  rings  appear  bluish, 
owing  to  circles  of  dispersion  falling  on  them.  A  little  closer,  and  the  black  rings 
become  white  or  yellowish-white,  being  covered  by  circles  of  dispersion  and  diffusion. 

brought  to  a  focus  about  0.5  mm.  in  front  of  the  red.  Under 
ordinary  circumstances  this  produces  no  confusion ;  and  yet  that 
this  defect  is  inherent  in  the  human  eye  may  be  readily  demon- 
strated. If  Fig.  354  is  brought  very  close  to  the  eyes — so  close 
that  the  two  crystalline  lenses  cannot  accommodate  for  it — the 
white  rings  become  bluish  on  account  of  circles  of  dispersion  fall- 
ing on  them,  and  if  brought  a  little  closer,  the  black  rings  become 
of  a  yellowish-white  color.  This  dispersion  also  explains  irradia- 
tion. 


SENSE  OF  SIGHT. 


575 


The  Iris. — The  iris  possesses  two  sets  of  muscular  fibers,  the 
circular  and  the  radiating.  Some  authorities  question  the  existence 
of  the  radiating  muscular  fibers,  regarding  them  as  elastic  rather 
than  contractile,  and  explain  dilatation  of  the  pupil  by  supposing 
that  the  circular  fibers  cease  to  contract,  and  that  by  the  elasticity 
of  the  radiating  fibers  the  pupillary  margin  of  the  iris  is  drawn 
outward.  It  seems  to  us,  however,  that  the  existence  of  contrac- 
tile radiating  fibers  has 
been  sufficiently  demon- 
strated. By  the  enlarge- 
ment or  diminution  of 
the  size  of  the  pupil  the 
amount  of  light  which  is 
permitted  to  pass  into  the 
eye  is  regulated.  The 
pigment  in  the  iris  makes 
it  opaque,  and  thus  only 
such  light  as  enters  the 
pupil  can  reach  the  retina. 
We  have  seen  that  it  is 
the  iris  which,  excluding 
the  marginal  rays,  mini- 
mizes spherical  aberra- 
tion ;  and  that  contrac- 
tion of  the  pupil  takes 
place  during  accommo- 
dation. The  three  func- 
tions of  the  iris  may, 
therefore,  be  regarded  as 

(1)  to  regulate  the  amount  ^/«  '    \     |-|_    —Vophth 

of  light  which  falls  upon 
the  retina  ;  (2)  to  minimize 

spherical  aberration  ;   and     Course  of  constrictor  nerve-fibers  

(3)    to    assist    the    accom-     Course  of  dilator  nerve-fibers  - 

modative  apparatus  in  the         FIG.  355.— Diagrammatic  representation  of  the 

production  of  distinct  vi-     ^f.v_es  governing  the  pupil :  //,  optic  nerve  ;  Lg, 


le 


sion  for  near  objects. 


ciliary  ganglion ;  r.b,  its  short  root   from  JIT, 
motor  oculi  nerve ;  sym,  its  sympathetic   root ; 

In   the    changes  which     r-l>  ^ts  l°ng  ro°*  from  V,  ophthalmonasal  branch 
,    i  i      '    •      ,  i  of  ophthalmic  division  of  fifth  nerve ;  s.c,  short 

take  place  in  the  iris,  two    cniary  nerves ; 
sets  of  nerves  are  involved 


;  I.e.,  long  ciliary  nerves  (Foster). 


(Fig.  355)  :  (1)  Those  of  the  third  nerve  or  oculomotorius ;  and  (2) 
those  of  sympathetic  origin.  The  third  nerve  supplies  the  circular 
fibers,  and  consequently  section  of  this  nerve  paralyzes  these  fibers, 
and  dilatation  of  the  pupil  occurs.  When  the  third  nerve  is  stimu- 
lated, the  circular  fibers  contract,  causing  a  diminution  in  the  size 
of  the  pupil.  The  sympathetic  supplies  the  radiating  fibers,  and 


576  THE  NERVOUS  SYSTEM. 

its  section  paralyzes  these  fibers,  causing  contraction  of  the  pupil, 
while  its  stimulation  produces  dilatation. 

Mydriatics  are  drugs  which  cause  the  pupil  to  dilate  ;  atropin 
is  a  well-known  mydriatic.  Cocain,  daturin,  and  hyoscyamin 
likewise  produce  dilatation  of  the  pupil,  and  are  therefore  mydri- 
atics. 

Myotics  are  drugs  which  produce  contraction  of  the  pupil. 
Prominent  in  the  list  of  myotics  are  eserin,  pilocarpin,  and 
morphin.  The  mydriatics  probably  act  by  paralyzing  the  oculo- 
motorius  and  stimulating  the  sympathetic.  When  large  doses  are 
used,  the  circular  fibers  may  be  paralyzed  directly.  Myotics 
paralyze  the  sympathetic  and  stimulate  the  oculomotorius. 

In  addition  to  producing  dilatation  of  the  pupil,  the  mydriatics 
paralyze  the  accommodation,  so  that  as  long  as  their  effect  lasts  it 
is  impossible  to  focus  the  eye  for  near  objects.  Myotics,  besides 
contracting  the  pupil,  cause  a  contraction  of  the  ciliary  muscle, 
and  thus  the  lens  is  adjusted  for  near  objects. 

When  light  falls  upon  the  retina  this  portion  of  the  eye  is 
stimulated,  and  the  impression  is  carried  by  the  optic  nerve  to  the 
brain,  and  there  motor  impulses  are  generated  which  are  trans- 
mitted through  the  third  nerve  to, the  sphincter  of  the  iris,  causing 
it  to  contract ;  this  is,  therefore,  a  reflex  act.  When  one  goes 
from  the  dark  into  the  light,  the  pupil  contracts,  but  this  contrac- 
tion lasts  only  a  short  time,  and  is  followed  by  dilatation,  and  in 
a  few  minutes  the  size  of  the  pupil  is  about  the  same  as  at  first. 
If,  on  the  other  hand,  one  goes  from  the  light  into  the  dark,  there 
is  at  first  a  dilatation  of  the  pupil,  then  a  contraction,  and  in  about 
twenty  minutes  the  pupil  is  as  it  was  before  the  dilatation.  These 
observations  demonstrate  that  there  are  other  influences  than  the 
incidence  of  light  upon  the  retina  to  produce  the  changes  in  the 
pupil. 

The  Retina. — As  odors  excite  the  olfactory  apparatus  and  savors 
excite  the  gustatory,  so  does  light  excite  the  retina.  As  neither 
odors  nor  savors  reach  the  brain,  where  smell  and  taste  are  pro- 
duced, but  only  the  nerve-impulses  which  they  excite  and  which 
the  olfactory  and  gustatory  nerves  transmit,  so  when  the  light- 
waves fall  upon  the  retina  they  go  no  farther ;  but  the  nerve-im- 
pulses which  they  there  excite  are  carried  to  the  brain  by  the  optic 
nerve  and  produce  the  sensation  called  "  light."  Thus  it  is  that  a 
blow  upon  the  eye  or  an  injury  to  the  optic  nerve  produces  in  the 
brain  the  impression  of  a  flash  of  light,  although  the  room  in 
which  the  blow  or  injury  was  received  may  be  absolutely 
dark. 

That  the  optic  nerve  is  itself  insensitive  to  light  is  shown  by 
the  fact  that  at  the  point  where  it  enters  the  eye,  forming  the  optic 
disk,  is  the  "blind  spot/'  at  which  there  is  an  entire  absence  of 
sight.  This  fact  may  be  demonstrated  in  the  following  simple 


SENSE  OF  SIGHT.  577 

way:  Look  with   the   right   eye  at  the  round  black  spot  here 
printed, 


closing  the  left  eye,  and  holding  the  book  six  inches  from  it.  The 
spot  and  the  cross  can  both  be  seen.  Now  carry  the  book  away 
from  the  face  farther  and  farther,  still  looking  at  the  spot.  A 
point  will  be  reached  where  the  cross  will  at  once  disappear,  and 
when  this  occurs  the  light  from  the  cross  falls  upon  the  optic  disk. 
If  the  book  is  carried  still  farther,  the  cross  will  again  come  in 
sight. 

There  is  no  doubt  that  the  portion  of  the  retina  which  reacts 
to  the  stimulus  of  light  is  the  layer  of  rods  and  cones,  and  of  this 
layer  the  cones  are  especially  sensitive.  This  is  shown  by  the 
fact  that  the  macula  lutea  (yellow  spot)  is  the  portion  of  the  retina 
which  is  the  most  sensitive,  and  here  there  are  no  nerve-libers,  but 
rods  and  cones,  and  in  the  fovea  centralis,  which  is  the  most  sensi- 
tive portion  of  the  macula,  only  cones  are  found. 

Purkinje's  Figures. — It  may  also  be  shown  by  the  following 
experiments  :  1.  If  in  a  dark  room  a  small  candle-flame  is  moved 
to  and  fro,  close  to  and  at  the  side  of  the  eye,  while  the  latter  is 
directed  toward  the  dark,  an  outline  of  the  blood-vessels  of  the 
retina  will  be  seen.  2.  Or,  if  after  the  eyes  have  been  closed  for 


FIG.  356. — Method  of  rendering  the  retinal  blood-vessels  visible  by  concentrating 
a  beam  of  light  on  the  sclerotic.  From  the  brightly  illuminated  point  of  the  scle- 
rotic, a,  rays  issue,  and  a  shadow  of  a  vessel,  r,  is  cast  at  a'.  It  is  referred  to  an  ex- 
ternal point,  a",  in  the  direction  of  the  straight  line  joining  a'  with  the  nodal  point. 
When  the  light  is  shifted  so  as  to  be  focussed  at  b,  the  shadow  cast  at  b'  is  referred  to 
b" — i.  e.,  it  appears  to  move  in  the  same  direction  as  the  illuminated  point  of  the 
sclerotic  (Stewart). 

some  time,  as  upon  awaking  from  sleep,  the  eyes  are  directed  for 
an  instant  to  a  white  ceiling,  an  outline  of  the  retinal  blood-vessels 

37 


578  THE  NERVOUS  SYSTEM. 

may  be  seen.  If  the  eye  is  quickly  closed  and  again  opened,  this 
outline  may  be  again  seen,  and  this  may  be  repeated  several  times. 
3.  A  third  method  of  demonstrating  the  retinal  vessels  is  by  con- 
centrating a  strong  light  on  the  sclerotic,  at  a  part  as  distant  as 
possible  from  the  cornea,  by  means  of  a  lens,  as  is  shown  in  Fig. 
356.  4.  If  a  card  is  perforated  with  a  pin,  and  then  held  close 
to  the  cornea,  and  through  the  pinhole  light  from  a  lamp  or 
other  source  of  illumination  is  allowed  to  fall  on  the  retina, 
when  the  card  is  moved  rapidly  up  and  down  or  from  side  to  side, 
but  not  so  much  as  to  prevent  the  light  from  entering  the  pupil, 


FIG.  357 — Figure  to  illustrate  the  principle  of  the  ophthalmoscope.  Kays  of 
light  from  a  point,  P,  are  reflected  by  a  glass  plate,  M  (several  plates  together  in 
Helmholtz's  original  form),  into  the  observed  eye  E'.  Their  focus  would  fall,  as 
shown  in  the  figure,  at  P7,  a  little  behind  the  retina  of  E'.  The  portion  of  the 
retina  A  B  is  therefore  illuminated  by  diffusion  circles ;  and  the  rays  from  a  point 
of  it,  F  will,  if  E'  is  emmetropic  and  unaccommodated,  issue  parallel  from  E'  and 
be  brought  to  a  focus  at  F'  on  the  retina  of  the  (emmetropic  and  unaccommodated) 
observing  eye  E. 

a  shadow  of  the  blood-vessels  of  the  retina  will  be  seen.     These 
shadows  of  the  retinal  blood-vessels  are  Purkinje's  figures. 

The  retinal  blood-vessels  do  not  extend  beyond  the  inner 
nuclear  layer,  and  the  fact  that  these  vessels  cast  a  shadow  when 
light  is  admitted  to  the  eye,  as  in  the  experiments  just  referred  to, 
demonstrates  that  the  sensitive  portion  of  the  retina  lies  behind 
the  blood-vessels,  and  the  distance  behind  can  be  calculated  by 
measuring  the  amount  of  change  of  position  the  shadows  undergo 
when  the  light  is  moved  about.  This  has  been  done,  and  the 
distance  has  been  ascertained  to  be  about  0.2  mm.  to  0.3  mm. 
behind  the  vessels,  which  corresponds  to  the  layer  of  rods  and 
cones. 


SENSE  OF  SIGHT. 


579 


Circulation  of  Blood  in  the  Retina. — Not  only  is  it  possible  to 
see  the  shadow  of  the  retinal  blood-vessels,  but  the  movement  of 


FIG.  358. — Diagram  of  the  direct  method  with  the  formation  of  an  upright  image. 
Rays  from  the  source  of  light  L  are  received  upon  the  concave  mirror  M,  and  con- 
verged upon  the  observed  eye  Obd.,  within  which  they  cross  and  illuminate  an  area 
of  its  fundus.  From  an  area  A  B  thus  lighted,  rays  pass  out  of  the  pupil  (parallel 
if  it  he  emmetropic,  as  here  represented)  through  the  sight-hole  of  the  mirror,  and, 
entering  the  observer's  eye,  Obr.,  are  fociissed  upon  the  retina.  An  image  is  there 
formed  as  though  the  object  seen  was  at  a  great  distance,  and  the  perceptive  centers 
project  it  into  space  as  though  the  object  was  at  some  arbitrary  distance  (e.  g.,  25 
cm.).  By  the  laws  of  magnification  by  a  simple"  lens  the  image  is  embraced  between 
the  lines  passing  from  the  optical  center  of  the  magnifying-lens  (the  refracting 
system  of  the  observed  eye),  through  the  extremities  of  the  object,  and  has  the  size 
A'  B',  A"  B",  etc.,  according  to  the  distance  of  projection  (Randall). 

the  corpuscles  within  these  vessels  can  also  be  seen  if  the  eye  is 
directed  toward  the  sky.     They  appear  as  bright  little  bodies, 


FIG.  359. — Diagram  of  the  indirect  method,  giving  an  inverted  image :  rays  from 
the  source  of  light  L,  converged  toward  the  observed  eye  Obd  by  the  concave  mirror 
M,  are  intercepted  by  the  lens  Obj,  and  after  coming  to  a  focus  diverge  again  and 
light  up  the  fundus.  From  a  part  of  the  illuminated  fundus  A  B  rays  pass  out  of 
the  pupil  to  be  again  intercepted  by  the  lens  0,  and  form  an  inverted  real  image  at 
its  anterior  focus  A'  B'.  This  real  image  is  viewed  by  the  observer's  eye  behind  the 
sight-hole  of  the  mirror  with  the  aid  of  a  magnify  ing-lens  Oc,  and  is  seen  enlarged, 
as  at  A"  B"  (Randall). 

moving  rapidly  and  uniformly  through  the  field.     If  cobalt  glass 
is  held  in  front  of  the  eyes,  the  corpuscles  are  more  readily  dis- 


580  THE  NERVOUS  SYSTEM. 

Jf  • "  * 

cernible.    The  velocity  of  the  flow  of  blood  in  the  capillaries  of 
the  retina  is  from  0.5  mm.  to  0.9  mm.  per  second. 

Intra-ocular  Images. — In  addition  to  the  blood-vessels  and 
blood-corpuscles,  other  objects  within  the  eye  may  throw  shadows 
upon  the  retina ;  indeed,  any  opacity  iii  the  media  of  the  eye 
through  which  the  rays  of  light  pass  would  do  this,  as,  for  in- 
stance, the  muscce  volitantes.  These  are  little  bodies  floating  in 
the  vitreous,  which  are  supposed  to  be  the  remains  of  cells  or 
fibers  which  exist  during  fetal  life,  and  which  have  not  become 
converted  into  the  vitreous  humor,  as  have  most  of  the  cells  and 
fibers.  They  assume  various  shapes  in  different  individuals,  but 
the  shape  is  invariable  in  the  same  person.  They  may  appear 
as  a  string  of  beads,  or  in  the  form  of  streaks  or  granules. 

The  Ophthalmoscope. — This  is  an  instrument  by  means  of  which 
one  person  can  examine  the  eye  of  another  and  obtain  a  view  of 
the  retina.  Inasmuch  as  some  of  the  rays  of  light  which  enter 
the  eye  and  fall  upon  the  retina  are  reflected  from  the  surface  and 
are  brought  to  a  focus  again  at  the  source  of  illumination,  it  is  mani- 
fest that  without  some  special  device  it  would  be  impossible  to  see 
the  image  which  these  reflected  rays  make,  for  to  have  the  eye  of 
the  observer  in  the  path  of  these  reflected  rays  would  cut  off  the 
light  which  caused  them.  To  overcome  this  obstacle,  Helmholtz 
devised  the  ophthalmoscope,  which  consisted  of  several  plates  of 
glass,  one  upon  another  (Fig.  357),  that  reflect  rays  of  light  from 
a  lamp  or  other  source  of  illumination  into  an  eye  to  be  examined ; 
these  rays  illuminate  the  retina,  and  those  that  are  reflected  issue 
from  the  observed  eye  and  are  brought  to  a  focus  on  the  retina  of 
the  observer.  The  observed  eye  and  that  of  the  observer  are  con- 
sidered to  be  emmetropic  and  in  a  condition  of  negative  accommo- 
dation or  accommodative  rest.  A  reference  to  Fig.  357  will  render 
this  explanation  clearer.  At  the  present  time  glass  plates  are  not 
used,  but  in  their  place  a  concave  mirror,  with  an  opening  in  it, 
through  which  the  observer  can  look.  There  are  two  methods  of 
using  the  ophthalmoscope :  the  direct  (Fig.  358)  and  the  indirect 
(Fig.  359).  These  will  be  readily  understood  after  an  examination 
of  the  illustrations  and  their  respective  legends. 

It  is  customary,  though  not  absolutely  necessary,  before  making 
an  ophthalmoscopic  examination  to  drop  into  the  eye  a  solution 
of  atropin  of  a  strength  of  two  grains  to  the  ounce.  This  paralyzes 
the  accommodation  and  dilates  the  pupil.  The  examination  is 
conducted  in  a  dark  room. 

The  illuminated  retina  produces  a  red  glare,  the  reflex,  which, 
as  the  observed  turns  his  eye  slightly  inward,  becomes  lighter 
in  color,  because  of  the  white  surface,  the  optic  disc,  from  which 
the  light  is  reflected  when  the  eye  is  in  this  position  ;  in  its  center 
is  the  porus  opticus,  with  the  arteria  centralis  retince,  and  radiating 
from  this  are  its  branches ;  veins  also  are  seen.  The  macula  lutea 
and  thefovea  centralis  may  likewise  be  discerned. 


SENSE  OF  SIGHT.  581 

The  ophthalmoscope  is  used  to  detect  changes  in  the  retina,  as 
in  Bright' s  disease  of  the  kidneys,  and  also  for  testing  errors  of 
refraction,  as  in  myopia  and  hypermetropia.  For  this  latter 
purpose  skiascopy  also  is  employed,  which  is  defined  as  "  a  method 
of  determining  the  refraction  of  the  eye  by  examining  the  move- 
ments of  light  and  shadow  across  the  pupil  when  the  retina  is 
illuminated  by  light  thrown  into  the  eye  from  a  moving  mirror." 

Light. — The  word  " light"  is  used  in  two  senses:  1.  With 
reference  cO  the  sensation  produced  in  the  brain  ;  and  2.  With 
reference  to  the  cause  of  that  sensation. 

Light,  the  cause,  is  defined  as  "  the  form  of  radiant  energy  that 
acts  on  the  retina  of  the  eye,  and  renders  visible  the  objects  from 
which  it  comes ;  the  illumination  or  radiance  that  is  apprehended 
by  the  sense  of  vision"  (Standard  Dictionary).  It  is  "  a  periodic 
disturbance  in  a  very  subtle  and  highly  elastic  medium  which  is 
supposed  to  exist  everywhere  in  space,  even  pervading  the  inter- 
molecular  spaces  in  matter.  This  medium  is  known  as  the  ether, 
and  vibrating  disturbances  in  it  give  rise  to  all  the  phenomena  of 
radiant  energy.  These  disturbances  are  propagated  through  it  as 
waves,  not  of  compression  and  rarefaction,  but  more  like  those  of 
the  rope,  the  direction  of  vibration  being  transverse  to  that  of 
propagation  "  (Carhart  and  Chute).  The  reference  to  "  the  rope  " 
is  to  an  experiment  of  laying  a  soft-cotton  rope,  about  5  feet  long, 
on  a  floor,  and  then,  holding  one  end  of  the  rope  in  the  hand,  setting 
up  vibrations  in  it  by  a  quick  up-and-down  movement  of  the  hand. 

When  these  waves  in  the  ether  reach  the  retina  they  produce 
the  sensation  of  sight,  and,  as  has  been  stated,  the  portion  of  the 
retina  which  is  sensitive  to  light  is  the  layer  of  rods  and  cones. 
Just  how  this  is  accomplished  is  not  known.  Various  theories 
have  been  advanced  to  explain  it :  (1)  That  the  waves  of  light  be- 
come waves  of  heat  and  thus  act  as  thermic  stimuli  to  the  rods  and 
cones ;  (2)  that  the  waves  of  light  become  waves  of  electricity,  and 
that  the  stimuli  are  electric;  and  (3)  that  these  waves  produce 
certain  chemical  changes,  so  that  the  stimuli  are  chemical.  The 
first  and  second  theories  may  be  passed  by  with  a  mere  men- 
tion, and,  although  the  third  is  far  from  proved,  yet  there  are  facts 
which  make  the  theory  worthy  of  attention  and  continued  investiga- 
tion, as  a  result  of  which  the  true  explanation  may  be  forthcoming. 

In  the  outer  portions  of  the  rods  of  the  retina  is  a  pigment, 
rhodopsin  or  visual  purple,  which,  when  the  retina  is  exposed  to 
light,  becomes  red,  then  orange,  then  yellow,  and  finally  fades 
away.  When  the  eye  is  exposed  to  light,  the  pigmented  epithe- 
lium of  the  retina  sends  pigmented  processes  between  the  rods 
and  cones,  and  this  pigment,  fuscin,  forms  visual  purple  again, 
and  this  reappears  in  the  rods.  If  the  pigmentary  layer  is  sepa- 
rated from  the  other  layers  of  the  retina,  the  formation  of  the 
rhodopsin,  after  it  has  been  bleached  by  light,  does  not  occur.  If 
an  eye,  after  having  been  protected  from  the  light  for  a  con- 


582 


THE  NERVOUS  SYSTEM. 


siderable  time,  is  then  exposed  so  as  to  receive  the  image  of 
a  window  upon  the  retina  for  a  time  varying  from  several  seconds 
to  several  minutes,  according  to  the  intensity  of  the  light,  and 
the  retina  is  then  removed  and  inspected  in  a  red  light,  the 
image  of  the  window  will  be  seen  in  it.  Such  an  image  is  an 
optogram,  and  is  due  to  the  action  of  the  light  on  the  visual  purple, 
bleaching  it  in  some  places,  and  but  little  affecting  it  in  others. 
This  image  may  be  preserved,  or,  as  photographers  say,  "  fixed," 
by  putting  the  retina  in  a  4  per  cent,  solution  of  alum. 

While  it  might  at  first  seem  as  if  these  changes  in  the  rhodopsin 
explained  what  actually  took  place  in  the  eye  when  the  waves  of 
the  luminiferous  ether  reached  the  retina  and  produced  the  sensa- 


FIG.  360.— Model  to  illustrate  astigmatism. 

tion  of  light,  still  the  absence  of  this  coloring-matter  from  the 
cones,  which  exist  without  the  rods  in  the  fovea  centralis,  where 
sight  is  most  acute,  would  alone  be  sufficient  proof  that  the  visual 
purple  is  not  essential  to  vision.  Some  animals  possessing  sight 
have  no  visual  purple  even  in  the  rods. 

Engelmann  has  described  a  shortening  and  a  thickening  of  the 
cones  of  frogs  and  fishes  under  the  stimulation  of  light,  and  a 
lengthening  in  the  absence  of  light,  but  as  to  the  connection  be- 
tween these  changes  in  the  cones  and  sight,  nothing  is  known. 

The  eye  is  able  not  only  to  see  objects,  but  to  take  cognizance 
of  certain  facts  in  connection  with  them,  such  as  their  form,  size, 
distance,  and  color. 


SENSE  OF  SIGHT. 


583 


Form. — Plane  surfaces  can  be  seen  with  either  eye  alone,  but 
solid  bodies  require  the  combined  use  of  bofch  eyes,  or  binocular 
vision,  in  order  that  their  solidity  may  be  appreciated.  If  a  solid 
object  is  looked  at  with  the  left  eye,  while  the  right  eye  is  closed, 
and  then  with  the  right  eye  while  the  left  is  closed,  it  will  be  ob- 
served that  with  the  left  eye  more  of  the  left  side  of  the  object  is 
seen  than  with  the  right  eye,  and  with  the  right  eye  more  of  the 
right  side  of  the  object  than  with  the  left  eye.  The  two  images 
produce  the  effect  in  the  brain  of  a  single  solid  body.  This 
principle  is  made  use  of  in  the  stereoscope  (Fig.  361).  The 
picture  which  is  seen  with  this  instrument  is  double,  each  having 
been  taken  with  a  separate  lens, 
so  that  when  their  images  are 
thrown  on  the  retina  the  effect  is 
as  if  both  eyes  were  looking  at 
the  scene  represented  in  the  pho- 
tographs. 

Identical  Points.  —  It  would 
seem  a  priori  that  each  retinal 
image  would  produce  its  own  ef- 
fect upon  the  brain,  and  that,  in- 
stead of  seeing  a  single  object,  it 
would  appear  double.  The  theory 
of  identical  or  corresponding  points 
has  been  advanced  to  explain  what 
actually  takes  place.  If  one  retina 
is  in  imagination  placed  upon  the 
other,  the  foveae  centrales  super- 
imposed the  one  upon  the  other, 
all  the  other  points  of  the  retinae 
similarly  'superimposed  are  iden-  The  prisms  refract  the  rays  coming 

tioil  or  oorresnondino*  noints   and     from  the  points  c'  r  of  the  Pictures  ab 
ing  po  nis,  anc     and  a^  so  that  they  appear  to  come 

images   formed   upon    such    points  from  a  single  point,  q.     Similarly  the 

will   in   the   brain   produce  the  ef-  points  a  and  a  appear  to  be  situated  at 

„    J       ...      ,         .   .  r         ,T7,          , ,  /,  and  the  points  6  and  ft  at  <<>. 
feet  or  single  vision.      When  the 

images  of  an  object  are  not  formed  upon  identical  points,  double 
vision  or  diplopia  results.  If,  therefore,  while  looking  at  an  object 
we  press  with  the  finger  upon  the  outer  side  of  one  eye  so  as  to 
turn  it  a  little  inward,  we  see  the  object  double. 

Size. — The  size  of  objects  is  determined  by  two  factors :  The 
size  of  the  visual  angle  which  they  subtend,  and  their  distance 
from  the  observer.  Helmholtz  has  demonstrated  that  an  object 
which  subtends  a  visual  angle  of  less  than  50"  cannot  be  seen  by 
the  unaided  emmetropic  eye.  This  corresponds  to  an  image  on  the 
retina  of  3.65  p..  The  diameter  of  each  cone  in  the  macula 
lutea  is  about  3  p.  Kolliker  gives  it  as  4  p.  to  5  p.  In  other 
words,  if  an  object  does  not  make  an  image  on  the  retina  large 


FIG.  361.— Brewster's  stereoscope: 


584  THE  NERVOUS  SYSTEM. 

enough  to  stimulate  a  cone,  it  does  not  come  within  the  range  of 
vision. 

Distance. — It  is  impossible  to  judge  of  the  distance  of  objects 
except  by  experience  ;  thus  a  child  reaches  for  everything  it  sees, 
irrespective  of  the  distance  from  it  the  objects  may  be ;  and  persons 
who,  having  been  blind  from  birth,  are  in  maturer  years  endowed 
with  sight — by  operation,  for  instance — bear  testimony  that  every- 
thing seems  to  be  immediately  in  front  of  them.  If,  however,  the 
size  of  an  object  is  known,  then  the  size  of  its  image  on  the  retina 
determines  our  estimate  of  its  distance.  Conversely,  if  we  know 
the  distance  of  an  object,  then  the  image  which  that  object  produces 
on  the  retina  is  the  determining  factor  in  our  judgment  of  its 
actual  size.  If,  therefore,  our  judgment  of  the  distance  of  an 
object  from  us  is  erroneous,  so  will  be  our  judgment  of  its  size, 
and  vice  versa.  If,  for  instance,  a  ship  is  seen  through  a  fog,  we 
suppose  that,  being  indistinctly  seen,  it  is  at  a  considerable  dis- 
tance from  us,  although,  as  a  matter  of  fact,  it  may  be  quite  near, 
and  making  an  image  of  considerable  size  upon  the  retina,  we  judge 
the  ship  to  be  larger  than  it  actually  is.  It  is  a  well-known  fact 
that  the  moon  seems  larger  to  an  observer  when  near  the  horizon 
than  when  near  the  zenith,  although,  as  a  matter  of  fact,  it  is  nearer 
by  about  4000  miles,  half  the  diameter  of  the  earth,  when  in  the 
zenith,  and  should  therefore  a  priori  seem  larger,  but  when  it  is 
near  the  horizon  we  have  terrestrial  objects  to  compare  it  with, 
while  when  in  the  zenith  there  is  nothing  with  which  to  com- 
pare it. 

The  correctness  of  this  explanation  has  been  questioned  by  a 
critic,  who  says :  "  The  moon  looks  large  when  rising  on  Salisbury 
Plain,  on  which  there  is  no  conspicuous  terrestrial  object  with 
which  it  can  be  compared,  and  looks  small  at  its  zenith  when  close 
to  the  vane  of  the  spire  of  Salisbury  Cathedral,  the  size  and  dis- 
tance of  which  are  well  known.  It  is  probably  an  affair  of  re- 

ft  •  ,,  A  J 

fraction." 

As  this  illusion  is  almost  universal,  and  one  of  great  interest, 
the  writer  deemed  it  worth  while  to  obtain  the  views  of  several 
well-known  physicists.  Among  those  written  to  was  Prof.  Spice, 
of  Cooper  Union,  New  York.  In  commenting  on  the  criticism 
above  quoted,  he  says  :— "  Though  it  is  true  that  there  is  no  l  con- 
spicuous'  object  in  sight,  still  there  is  at  least  the  Plain— and  this 
would  give  one  an  idea  of  distance.  With  reference  to  the  prox- 
imity to  the  vane  on  the  cathedral  spire,  I  would  suggest  that 
unless  an  observer  were  on  the  spire  the  vane  itself  would  (of 
necessity)  look  small,  and  therefore  would  not  tend  to  make  the 
moon  look  large.  As  to  the  idea  of  refraction  increasing  the  ap- 
parent size :  The  refraction  at  the  horizon  is  about  34*'  +  ;  the 
apparent  diameter  of  the  moon  is  about  31'  +  so  if  the  moon 


SENSE  OF  SIGHT.  585 

were  just  below  the  horizon  it  would  appear  just  on  the  horizon. 
Further,  if  the  moon  were  just  on  the  horizon  the  lower  part  of 
the  moon  would  be  raised  (by  refraction)  more  than  the  upper 
pirt,  because  refraction  diminishes  rapidly  after  leaving  the  hori- 
zon, so  the  vertical  (apparent)  diameter  of  the  moon  would  be  less, 
but  the  horizontal  diameter  would  not  change — i.  e.,  the  area  (size) 
of  the  moon  at  the  horizon  would  be  smaller  by  refraction. 

"As  to  the  apparent  greater  size  of  the  moon  when  near  the 
horizon,  I  believe  that — as  stated  in  most  astronomy  books,  say 
Charles  Young's  or  Todd's  New  Astronomy — it  is  due  to  the  fact 
that  in  looking  at  the  moon  in  that  position  we  see  many  well- 
known  objects  as  well :  houses,  trees,  etc. ;  and  as  we  have  a  rough 
idea  of  the  size  of  these  objects  and  also  know  they  are  nearer  us 
than  the  moon  is,  we  get  the  idea  of  largeness.  In  the  zenith  we 
have  no  objects  for  comparison,  and  as  angular  magnitude  alone 
conveys  no  meaning,  we  have  nothing  to  guide  (or  misguide)  our 
judgment.  Of  course,  when  in  the  zenith,  the  moon's  angular  size 
is  very  slightly  greater,  as  we  are  nearly  4000  miles  nearer — i.  e., 
by  the  radius  of  the  earth.  I  may  remark  that  the  common  notions 
as  to  .the  moon's  size  are  curious :  one  person  may  say  it  looks  as 
4  big  as  a  dinner-plate/  and  another,  ( as  big  as  a  half-dollar/  but 
in  no  case  which  I  have  examined  have  these  thoughtful  people 
made  any  mention  of  how  far  from  them  the  dinner-plate  was  sup- 
posed to  be  at  the  time." 

Prof.  C.  A.  Young,  the  well-known  astronomer,  of  Princeton 
University,  was  written  to  for  his  explanation  of  the  phenomenon ; 
his  answer  is  as  follows : — "As  to  the  phenomenon  to  which  you 
refer,  the  apparent  enlargement  of  celestial  objects  near  the  horizon, 
I  am  satisfied  with  the  generally  received  explanation  that  it  is 
due  to  the  fact  that  while  the  angular  diameter  of  the  object  re- 
mains practically  the  same  as  at  the  zenith  (really  a  little  less),  the 
object  is  instinctively  referred  to  a  greater  distance  because  of  the 
number  of  intervening  objects  by  which  we  judge  of  distance. 

"  If  the  sun  or  moon  be  looked  at  through  a  smoked  glass, 
which  leaves  the  disc  visible  while  hiding  the  horizon  and  inter- 
vening objects,  the  sun  or  moon  immediately  shrinks  to  the  same 
apparent  diameter  as  if  higher  up.  At  least  it  is  so  with  me,  and 
with  most  persons  whom  I  have  seen  try  the  experiment.  Look- 
ing through  a  tube  like  a  piece  of  gas-pipe  12  inches  long  is  just 
as  effectual;  what  is  necessary  is  to  cut  out  all  objects  and  the 
horizon  line  while  still  leaving  the  moon  (or  sun)  visible.  But 
some  persons  say  they  do  not  get  the  effect.  In  their  case  I  judge 
that  the  habitual  sense  of  the  horizon  as  distant  comes  in  to  main- 
tain the  illusion,  even  though  they  cannot  actually  see  it,  but  I  am 
aware  that  some  physiologic  psychologists  decline  to  accept  the 
explanation" 


586  THE  NERVOUS  SYSTEM. 

.« 

The  New  International  Encyclopaedia  regards  the  apparent 
enlargement  as  due  to  an  illusion  of  distance.  The  distance  be- 
tween the  observing  eye  and  the  horizon  seems  to  be  longer  than 
the  distance  between  the  eye  and  the  zenith,  owing  to  the  haziness 
of  the  air,  the  number  of  intervening  objects,  etc.  The  retinal 
image  being  practically  the  same  in  both  instances,  the  object  which 
the  mind  refers  to  a  greater  distance  appears  to  be  larger. 

Prof.  Pickering,  of  Harvard  College  Observatory,  in  his  book, 
The  Moon,  in  treating  of  this  subject,  says : 

"  The  true  angular  size  of  the  moon  is  about  half  a  degree ;  it 
can,  therefore,  always  be  concealed  behind  a  lead-pencil  held  at 
arm's  length.  The  sun  and  moon  when  rising  or  setting  appear 
to  most  persons  of  from  two  to  three  times  the  diameter  that  they 
have  when  near  the  meridian.  The  cause  of  this  phenomenon  has 
been  a  source  of  speculation  from  the  earliest  times.  Before  optical 
science  was  thoroughly  developed  some  thought  that  the  image 
was  really  magnified  by  the  vapors  near  the  horizon.  Not  only  is 
this  incorrect,  but  in  point  of  fact  the  sun  is  slightly  and  the  moon 
measurably  smaller  when  near  the  horizon,  because  they  are  farther 
off  than  when  overhead. 

"  The  true  explanation  is  twofold.  Human  estimates  of  angular 
dimensions  are  dependent  not  merely  on  the  angular  dimensions 
themselves,  but  also  on  several  extraneous  circumstances.  The 
case  is  analogous  to  our  estimates  of  height,  which  are  dependent 
primarily  on  the  real  height  of  the  object,  but  secondarily  upon 
its  bulk.  Thus,  a  pound  of  lead  feels  much  heavier  than  a  pound 
of  feathers. 

"  One  circumstance  affecting  our  estimates  of  angular  dimension 
is  the  linear  dimension  of  the  object  itself.  It  was  pointed  out  by 
Alhazen  about  nine  hundred  years  ago  that  if  we  hold  the  hand  at 
arm's  length  and  notice  what  space  it  apparently  covers  on  a  dis- 
tant wall,  and  then  move  the  hand  well  to  one  side  so  that  it  is  in 
front  of  some  very  near  object,  we  shall  find  that  it  will  appear  to 
us  decidedly  smaller  than  the  part  of  the  wall  which  it  previously 
covered.  ^  It  is  an  analogous  effect  which  makes  the  full  moon 
when  rising  or  setting  appear  larger  than  when  it  is  well  up  in  the 
sky.  On  the  horizon  we  can  compare  it  with  trees  and  houses, 
and  see  how  large  it  really  is ;  overhead  we  have  no  linear  scale 
of  comparison. 

"  It  is  certain  that  this  is  not  the  only  reason,  however,  nor 
even  the  chief  one,  that  makes  the  moon  appear  larger  when  near 
the  horizon.  The  same  optical  illusion  appears  when  at  sea,  and 
it  applies  also  to  the  constellations— for  example,  to  Orion.  When 
rising  they  appear  decidedly  larger  than  when  near  the  meridian, 
and  yet  no  comparison  of  their  size  with  that  of  terrestrial  objects 
is  usually  possible.  There  is  evidently  another  circumstance 


SENSE  OF  SIGHT. 


587 


affecting  our  estimates  of  angular  diameter.  The  explanation  of 
this  was  first  given  by  Clausius  about  thirty  years  ago,  .  .  .  but 
it  has  not  as  yet  got  into  the  text-books.  The  circumstance  chiefly 
affecting  our  estimates  of  size  depends  on  the  angular  altitude  of 
the  object  under  consideration. 

"  When  we  pass  under  an  archway  or  under  the  limb  of  a  tree 
we  know  that  we  are  nearer  to  the  object  than  we  are  when  we  see 
it  under  a  lower  altitude ;  at  the  same  time  it  appears  just  as  large 
to  the  average  person  angularly  as  it  does  when  we  are  several  feet 
farther  away.  We  are,  in  fact,  used,  all  our  lives  as  we  walk 
about,  to  see  objects  rapidly  shifting  their  angular  positions,  yet 
not  appearing  as  we  pass  them  any  larger  than  they  do  when  we 
are  slightly  more  distant  from  them.  We  thus  always  uncon- 
sciously make  some  compensation  in  our  minds  for  the  real  changes 
in  angular  size  that  actually  occur. 

"  If,  now,  the  limb  of  the  tree  that  we  passed  under,  instead  of 
really  growing  angularly  smaller  at  the  low  altitude  than  it  was 
when  overhead,  should  remain  of  the  same  angular  size  in  all  posi- 
tions, we  should  say  that  it  looked  larger  at  the  low  altitude. 
This  is  exactly  what  happens  in  the  case  of  the  heavenly  bodies. 
Unlike  all  terrestrial  objects,  they  are  practically  of  the  same  real 
angular  dimensions  when  on  the  horizon  that  they  are  in  the 
zenith.  We  involuntarily  apply  to  them  the  same  compensation 
that  we  are  accustomed  to  apply  to  terrestrial  objects,  and  are  thus 
naturally  surprised  to  see  that  they  appear  larger  at  the  lower 
altitude." 


FIG.  362. — Formation  of  solar  spectrum. 

Color. — When  a  beam  of  sunlight  passes  through  a  prism  it  is 
separated  by  dispersion  into  its  component  colors,  forming  a  solar 
spectrum  (Fig.  362),  the  red  rays  being  the  least  refracted,  and 
the  violet  rays  the  most.  The  color  depends  upon  the  rapidity  of 
vibration  or  the  length  of  the  waves ;  thus  the  red  waves  are  the 
longest  and  the  vibrations  the  least  rapid,  while  the  violet  are  the 
shortest  and  the  vibrations  the  most  rapid.  In  the  following 


588 


THE  NERVOUS  SYSTEM. 


table  are  given  the  wave-lengths  for  the  center  of  each  color  in 
ten-millionths  of  a  millimeter. 


Red 7000 

Orange      5972 

Yellow     5808 

Green    .  5271 


Blue       .    .    ...'.>- 4960 

Indigo 4383 

Violet    .  .    4059 


There  are  rays,  calorific  rays,  beyond  the  red  rays  whose  wave- 
lengths are  longer  than  the  red,  and  others  beyond  the  violet  whose 
wave-lengths  are  shorter  than  those  of  the  violet ;  these  latter  are 
the  actinic  rays  ;  neither  the  calorific  nor  the  actinic  rays  are  visi- 
ble. 

If,  after  the  dispersion,  a  second  prism  in  reversed  position 
(Fig.  363)  is  placed  in  the  path  of  the  colored  rays,  these  will  be 


FIG.  363. — Reunion  of  colored  rays  to  form  white  light. 

reunited,  and  will  emerge  from  the  second  prism  as  white  light. 
This  synthesis  of  light,  or  the  composition  of  white  light  by  the 
union  of  all  the  colors  of  the  spectrum,  may  be  brought  about  by 
the  union  of  certain  colors  without  using  all  of  them ;  thus  red 
and  bluish  green  will  produce  white  light,  as  will  also  orange  and 
light  blue.  Colors  which  when  mixed  produce  white  light  are 
complementary.  In  the  color  diagram  (Fig.  364)  this  relation  is 


FIG.  364.— Color  diagram. 

made  evident,  the  form  of  a  triangle  being  selected  around  which 
to  arrange  the  colors,  rather  than  a  circle,  for  the  reason  that  they 
do  not  act  equally  as  stimuli.  Red,  green,  and  violet  are  placed 
at  the  angles  on  the  Young-Helmholtz  theory  of  these  being  the 
primary  colors — i.  e.,  the  theory  thaf  the  other  colors  are  mixtures 
of  these  three  colors.  A  reference  to  this  diagram  shows  that  red, 
green,  and  violet,  represented  by  R,  G,  and  v,  make  white,  repre- 


SENSE  OF  SIGHT.  589 

sented  by  w.  The  colors  at  the  extremities  of  straight  lines  are 
complementary  colors ;  orange  and  blue,  o  and  B,  make  white,  w. 
But  neither  B  nor  o  is  at  the  extremities  of  the  line  from  n,  but, 
if  this  line  was  continued,  it  would  strike  the  curved  line  between 
B  and  G — i.  e.,  red  and  bluish  green  are  complementary  colors. 
One  can  see  also  from  this  diagram  what  color  results  from  the 
union  of  two  others.  Thus  red  and  yellow  will  produce  the  inter- 
mediate color,  orange ;  red  and  violet  will  produce  purple,  and 
this  and  green  will  produce  white.  If  complementary  colors  are 
put  beside  each  other,  both  colors  are  more  pronounced ;  on  the 
other  hand,  if  colors  which  are  not  complementary  are  so  placed, 
the  colors  are  subdued. 

It  may  be  well  here  to  refer  to  some  of  the  fundamental  facts 
in  connection  with  colors,  and  for  this  purpose  we  shall  quote 
statements  and  experiments  from  Elements  of  Physics,  by  Carhart 
and  Chute.  Color  is  not  a  property  inherent  in  objects — i.  e., 
bodies  have  no  color  of  their  own.  Thus  in  the  case  of  opaque 
bodies,  the  color  which  they  appear  to  have  depends  upon  the 
kind  of  light  which  they  reflect.  A  red  body  is  red  because  it 
absorbs  the  other  colors  of  the  spectrum  than  the  red  and  reflects 
this  color  from  its  surface.  If  all  the  colors  are  reflected  in  proper 
proportion,  the  body  appears  white.  This  can  be  proved  by 
looking  through  a  glass  prism  at  a  piece  of  white  paper  3  cm. 
long  and  2  mm.  wide,  pasted  on  a  piece  of  black  cardboard 
several  times  larger,  the  edges  of  the  prism  being  held  parallel 
to  the  length  of  the  strip.  The  image  seen  through  the  prism 
will  be  a  spectrum  similar  to  the  solar  spectrum.  If  a  piece 
of  red  paper  is  substituted  for  the  white  paper,  on  looking  through 
the  prism  the  red  end  of  the  spectrum  will  be  seen,  but  the  other 
colors  will  be  dim  or  absent.  If  a  blue  strip  is  looked  at,  the 
spectral  image  will  show  the  blue,  the  other  colors  being  lacking. 
In  other  words,  white  paper  is  white  because  it  reflects  all  the 
colors  in  due  proportion,  while  red  paper  reflects  only  red,  and 
blue,  only  blue.  If  in  the  red  of  the  solar  spectrum  a  piece  of 
red  paper  or  ribbon  is  held,  it  will  appear  brilliantly  red  ;  else- 
where it  will  be  nearly  black  ;  a  piece  of  blue  will  appear  blue  in 
the  blue  of  the  spectrum,  and  there  only.  The  color  of  opaque 
bodies  varies  as  the  light  which  falls  upon  them  varies ;  thus  if 
any  fabric  into  which  blue  or  violet  enters,  as  purple  and  pink, 
is  examined  by  artificial  lights,  all  of  which  are  deficient  in  blue 
and  violet  rays,  its  color  will  vary  from  that  which  it  has  in  sun- 
light. It  is  on  this  account  that  matching  colors  by  artificial 
light  is  so  difficult. 

Transparent  bodies,  on  the  other  hand,  are  colorless  when  they 
absorb  no  light — i.  e.,  transmit  it  all ;  or  when  they  absorb  all  the 
colors  in  like  proportion.  It  is  the  color  or  colors  which  are  trans- 
mitted that  give  the  color  to  transparent  bodies.  If  one  color  is 


590  THE  NERVOUS  SYSTEM. 

absorbed,  the  color  of  the  object  will  be  the  sum  of  the  colors 
that  are  transmitted. 

We  are  now  prepared  to  discuss  some  of  the  facts  which  have 
been  established  in  connection  with  the  sensation  of  color.  The 
union  of  the  spectral  colors  to  produce  white  light  may  be  demon- 
strated by  cutting  out  disks  of  colored  paper  (Fig.  365)  and 
attaching  them  to  a  whirling  machine  (Fig.  366),  or  complemen- 
tary colors  may  be  combined  in  the  same  way  with  the  same 
result ;  or,  again,  by  using  different  colors  various  combinations 
may  be  made.  This  may  be  called  a  physiologic  mixture  of  colors, 
and  is  thus  explained  :  When  the  retina  is  exposed  to  a  color,  this 
produces  a  certain  effect  which  remains  even  after  the  color  which 
produced  it  has  been  removed ;  if,  before  the  sensation  caused  by 
this  color  has,  disappeared,  the  retina  is  exposed  to  another  color, 
the  second  color  is  superimposed  upon  the  first,  and  if  the  two  are 
complementary,  the  effect  is  that  of  white  light,  as  when  these 


FIG.  365 —Disks  of  colored  paper.  FIG.  366.— Whirling  machine. 


colors  are  combined  by  a  prism.  If  the  revolving  disks  contain 
all  the  spectral  colors  in  due  proportion,  and  are  revolved  rapidly 
enough,  so  that  all  the  colors  produce  their  effect  on  the  retina 
before  the  sensation  produced  by  any  one  has  faded  away,  the 
effect  of  white  light  is  produced,  as  when  these  colors  are  united 
by  a  prism. 

Mixing  of  Pigments.— The  effects  just  described  as  being  pro- 
duced by  the  physiologic  mixture  of  colors  cannot  be  produced  by 
the  mechanical  mixture  of  pigments.  Although  blue  and  yellow 
when  mixed  upon  the  retina  produce  white,  yet  when  blue  and 
yellow  pigments  are  mechanically  mixed  the  resulting  color  is 
green  and  not  white.  If  a  broad'  line  is  drawn  on  a  blackboard 
with  a  yellow  crayon,  and  over  this  is  drawn  another  line  with  a 
blue  crayon,  the  resulting  color  will  be  green.  This  effect  is  ex- 
plained in  the  following  manner :  The  yellow  crayon  reflects  not 
only  yellow  light,  but  also  green  light,  and  absorbs  all  the  other 
colors.  The  blue  crayon  reflects  not  only  blue,  but  also  green,  and 


SENSE  OF  SIGHT.  591 

absorbs  all  the  others.  So  that  when  the  two  are  mixed,  the  only 
color  which  is  not  absorbed  by  the  crayon  is  green,  and  therefore 
the  line  appears  green. 

Nor  can  the  colors  which  are  transmitted  through  transparent 
bodies  be  united  to  produce  white  light,  or  the  combination  which 
the  mixture  of  colored  lights  produces  on  the  retina,  any  more 
than  can  the  pigments  mentioned  above,  and  the  reason  for  this  is 
obvious.  If,  for  instance,  sunlight  is  transmitted  through  red 
glass,  all  the  rays  which  produce  other  colors  than  red  are  absorbed, 
and  the  red  only  being  transmitted,  gives  the  red  color  to  the  glass. 
If  the  same  is  done  with  green  glass,  only  the  green  rays  will  be 
transmitted,  all  the  other  rays  being  absorbed.  If  now  white 
light  is  transmitted  through  red  glass,  only  the  red  will  remain, 
and  if  this  is  transmitted  through  green  glass,  no  light  will  come 
through,  for  green  glass  will  not  transmit  the  red  rays,  and  the 
green  rays  have  already  been  absorbed  by  the  red  glass.  To  pro- 
duce white  light  or  the  various  combinations  of  the  spectral  colors, 
the  rays  must  fall  upon  the  retina  and  the  colors  be  mixed  phy- 
siologically, the  mixture  producing  effects  which  are  interpreted 
by  the  brain. 

Young-Helmholtz  Theory  of  Color. — Inasmuch  as  this  theory 
was  advanced  by  both  Young  and  Helmholtz,  it  bears  the  name 
of  both.  It  is  based  on  the  view  that  there  are  in  the  retina  three 
substances  which  are  stimulated  by  the  three  primary  colors,  re- 
spectively, of  red,  green,  and  violet,  and  that  when  all  three  fall 
upon  the  retina  in  proper  proportion  the  sensation  of  white  is 
produced ;  and  when  any  two  of  the  three  stimulate  the  retina, 
the  effect  is  to  produce  some  intermediate  color,  as,  for  instance, 
violet  and  green  produce  blue ;  red  and  green,  yellow  and  orange ; 
red  and  violet,  purple.  That  such  substances  actually  exist,  there 
is  no  proof;  the  term  "  substance "  is  used  for  want  of  a  better 
one.  The  term  "  fiber  "  is  used  by  Helmholtz,  and  "  red  fibers," 
"  green  fibers,"  and  "  violet  fibers'"  are  spoken  of.  This  theory 
supposes,  also,  that  each  of  the  primary  colors  stimulates  to  some 
extent  all  the  three  substances,  but  one  is  stimulated  so  much 
more  than  the  others  that  the  effect  upon  the  others  is  not 
noticed.  Especially  marked  is  this  differentiation  of  the  red, 
green,  and  violet  near  the  fovea  centralis,  and  when  the  light  is 
not  too  intense.  If  the  light  falls  upon  the  portions  of  the  retina 
near  the  ora  serrata,  or  if  that  which  falls  on  the  retina  in  the 
neighborhood  of  the  fovea  is  of  very  little  or  of  very  great  inten- 
sity, all  the  rays  seem  to  stimulate  the  three  substances  alike,  for, 
under  such  circumstances,  the  colors  of  objects  are  not  readily 
made  out.  The  theory  has  been  advanced  that  the  power  to  dis- 
tinguish colors  resides  in  the  cones,  and  that  the  stimulation  of  the 
rods  by  light  gives  the  sensation  of  luminosity  without  color.  Von 
Kries  states  that  the  rods  are  color-blind,  their  stimulation  re- 


592  THE  NERVOUS  SYSTEM. 

suiting  in  the  sensation  of  luminosity  only ;  that  they  are  more 
easily  stimulated  than  the  cones,  and  are  particularly  responsive 
to  waves  of  short  wave-lengths ;  and  that  they  adapt  themselves 
to  light  of  varying  intensity. 

Hering  Theory  of  Color. — This  theory  supposes  the  existence 
of  three  substances  in  the  retina,  and  of  six  primary  color  sensa- 
tions, arranged  in  pairs,  white  and  black  forming  one  pair,  red 
and  green  another,  and  yellow  and  blue  the  third.  These  corre- 
spond, it  will  be  noticed,  to  complementary  color  sensations.  The 
three  substances  are  the  white-black,  the  red-green,  and  the  yellow- 
blue.  These  substances  are  supposed  to  be  susceptible  of  being 
affected  in  two  opposite  ways :  In  one  a  constructive  or  anabolic 
change  is  produced,  and  in  the  other  a  disintegrate ve  or  katabolic 
change.  If,  for  example,  all  the  spectral  colors  fall  upon  the 
white-black  substance,  katabolic  changes  occur  in  this  substance 
producing  the  sensation  of  luminosity ;  while  if  no  light  enters  the 
eye,  anabolic  changes  occur,  with  the  effect  of  producing  blackness. 
The  red  rays  falling  upon  the  retina  produce  katabolic  changes 
in  the  red-green  substance,  producing  the  sensation  of  red,  while 
the  green  produces  anabolic  changes,  and  the  resulting  sensation  is 
that  of  green.  Blue  rays  cause  anabolic  changes  in  the  yellow- 
blue  substance,  and  yellow  rays  cause  katabolic  changes  in  the  same 
substance.  These  changes  in  the  retinal  substances  produce  the 
sensations  of  color  when  transmitted  through  the  fibers  of  the 
optic  nerve  to  the  brain. 

Franklin  Theory  of  Color-sensation. — This  theory  supposes  that 
the  eye,  in  the  early  periods  of  development,  possesses  only  the 
white-black  or  gray  visual  substance,  and  is  therefore  sensitive  to 
luminosity  only,  and  not  to  color.  Later  this  substance  becomes 
modified  into  the  blue  and  yellow  substance,  and  then  into  the  red 
and  green.  For  a  further  account  of  this  theory  the  reader  is 
referred  to  the  American  Text-book  of  Physiology,  vol.  ii.,  p.  337. 

Birch  Modification  of  the  Young-Helmholtz  Theory. — This  ex- 
perimenter has  exposed  the  eye  to  sunlight  in  the  focus  of  a  burn- 
ing-glass behind  transparent  screens  of  different  colors,  with  the 
result  of  producing  a  temporary  color-blindness.  If  a  red  screen 
is  used,  the  eye  is  red-blind — i.  e.,  cannot  distinguish  the  color,  so 
that  if  scarlet  is  looked  at,  it  appears  black,  while  yellow  appears 
green  and  purple  appears  violet.  If  a  violet-colored  screen  is  used, 
violet  appears  black ;  purple  appears  crimson  ;  and  green,  a  bright 
green.  These  effects  are  due  to  fatigue  of  the  retina,  so  that  the 
color  to  which  the  retina  is  exposed  for  a  time  ceases  to  stimulate, 
and  that  color  ceases  to  be  recognized  while  the  other  colors  con- 
tinue to  stimulate.  Birch  found  that  after  exposure  to  yellow 
the  eye  was  blind  not  only  to  yellow,  but  to  red  and  green  also, 
which  primary  colors  in  the  Young-Helmholtz  theory  produce 
yellow.  He  concludes  that  there  are  not  only  the  three  primary 


SENSE  OF  SIGHT. 


595 


sun,  but  not  long  enough  to  produce  fatigue,  and  then  closed, 
a  bright  spot  of  light  is  seen  :  this  is  a  positive  after-image.  It 
remains  bright  for  but  a  short  time  and  then  changes  color, 
becoming  greenish  blue  or  bluish 
green,  blue,  violet,  purple,  and  red, 
and  then  fading  away  entirely.  It 
may  be  followed  by  a  negative  after- 
image. 

Visual  Judgment. — -We  have  al- 
ready referred  to  some  visual  judg- 
ments— as  to  form,  size,  distance, 
etc.  (p.  584).  It  is  a  common  say- 
ing that  "  seeing  is  believing,"  and 
yet  not  one  of  the  senses  is  more 
liable  to  deceive  its  possessor  than 
that  of  sight.  For  instance,  if  the 
vertical  and  horizontal  lines  in  Fig. 
367  are  compared,  the  vertical  will 
immediately  be  pronounced  the 
longer,  and  yet  when  accurately 
measured  it  will  be  found  that  each  is  exactly  4  cm.  in  length. 
This  tendency  to  overestimate  vertical  lines  is  attributed  to  the 
relative  weakness  of  the  superior  rectus  muscle  as  compared  with 
the  muscles  that  move  the  eyeball  horizontally.  The  difference  is 
said  to  be  from  30  to  50  per  cent,  in  height  and  40  to  53  per 


FIG.  367. — To  illustrate  the  overesti- 
mation  of  vertical  lines. 


FIG.  368. — To  illustrate  the  illusion  of  subdivided  space. 

cent,  in  area  of  cross-section  ;  owing  to  this  weakness  a  greater 
effort  is  required  to  turn  the  eyeball  upward,  and  the  effect  upon 
the  mind  is  that  of  turning  it  through  a  greater  distance ;  hence 
vertical  lines  seem  to  be  longer  than  they  really  are. 


596  THE  NERVOUS  SYSTEM. 

In  Fig.  368  the  space  between  A  and  B  seems  to  be  greater 
than  that  between  B  and  c,  and  yet  they  are  exactly  the  same. 
Any  space  like  that  between  A  and  B  which  is  subdivided  seems 
larger  than  that  which  is  undivided,  as  that  between  B  and  c. 
In  Fig.  368  D  appears  to  be  higher  than  it  is  broad,  and  E  broader 
than  it  is  high. 

So,  too,  Zollner's  lines  (Fig.  369)  are  very  illusory.  The  hori- 
zontal lines  appear  to  be  far  from  parallel,  and  yet  if  they  are 
looked  at  from  their  ends,  by  turning  the  page  sidewise,  their 

/  /  /  7  /////// 


\  \  \  \  \  \  v  v  v  v  v 


\  \  \  \  \  \  \  \  \  \  \ 

FIG.  369.—  Zollner's  lines. 

parallelism  is  at  once  apparent.  This  is  explained  by  the  fact 
that  acute  angles  are  apt  to  be  overestimated  and  obtuse  angles 
underestimated. 

In  Fig.  370  the  straight  line  A  appears  shorter  than  the  straight 
line  B,  though  it  is  of  exactly  the  same  length. 

Similar  illusions  might  be  multiplied  almost  indefinitely,  and 
yet  with  all  its  imperfections  the  human  eye  is  a  wonderful  organ. 
Some  one  has  said  that  it  is  so  defective  from  an  optical  standpoint 
that,  had  he  ordered  such  a  piece  of  apparatus  from  an  optician 


FIG.  370.— Illusion  of  space-perception  (Bowditch). 

and  it  had  been  delivered  with  as  many  defects,  he  would  have 
returned  it  and  refused  to  pay  for  it.  It  has  also  been  said,  in 
speaking  of  the  crystalline  lens,  that  an  optician  could  make  a 
better  lens  than  Nature  has  furnished ;  but  it  has  also  been  said 
that  he  could  not  make  so  good  an  eye.  And  finally,  Dr.  Bow- 
ditch,  in  his  excellent  discussion  of  "Vision,"  in  the  American 
Text-book  of  Physiology,  well  says :  "  When  we  reflect  upon  the 
difficulty  of  the  problem  which  Nature  has  solved,  of  constructing 
an  optical  instrument  out  of  living  and  growing  animal  tissue,  we 
cannot  fail  to  be  struck  by  the  perfection  of  the  dioptric  apparatus 


SENSE  OF  SIGHT. 


597 


of  the  eye  as  well  as  by  its  adaptation  to  the  needs  of  the  organism 
of  which  it  forms  a  part." 

Appendages  of  the  Eye.  —  Lacrimal  Apparatus. — To  keep 
the  conjunctiva  (the  mucous  membrane  covering  the  anterior  seg- 


FIG.  371. — Lacrimal  and  Meibomian  glands,  the  latter  viewed  from  the  posterior 
surface  of  the  eyelids.  (The  conjunction  of  the  upper  lid  has  been  partially  dis- 
sected off,  and  is  raised  so  as  to  show  the  Meibomian  glands  beneath.)  Jf,  free  border 
of  upper,  and  2,  free  border  of  lower  lid,  with  openings  of  the  Meibomian  glands; 
5,  Meibomian  glands  exposed,  and  6,  as  seen  through  conjunctiva  ;  7,  8,  lacrimal 
gland  ;  9,  its  excretory  ducts,  with  10,  their  openings  in  the  conjunctival  cul-de-sac; 
11,  conjunctiva  (Testut). 

ment  of  the  sclerotic  and  the  cornea  and  lining  the  lids)  moist  and 
in  normal  condition  is  the  function  of  the  tears.  They  are  secreted 
by  the  lacrimal  gland,  a  compound  racemose  gland  lodged  in  a 
depression  at  the  upper  and  outer  portion 
of  the  orbit.  Its  ducts,  about  seven  in 
number,  open  on  the  upper  and  outer  half 
of  the  conjunctiva  near  its  reflection  over 
the  eyeball.  At  the  edge  of  the  upper 
and  lower  eyelids,  at  their  inner  ex- 
tremities, are  openings,  puncta  lacrimalia, 
into  which  the  tears  pass  after  performing 
their  function.  These  openings  are  the 
beginnings  of  the  canaliculi  (Fig.  372), 
which  open  into  the  lacrimal  sac,  or 
the  dilated  upper  extremity  of  the 
nasal  duct,  which  discharges  at  the 
inferior  meatus  of  the  nose,  the  open- 
ing here  being  partially  closed  by  a 
fold  of  mucous  membrane,  the  valve 
of  Hasner. 

Meibomian  Glands. — On  the  posterior  surface  of  the   eyelids, 


FIG.  372.— 1,  Canaliculus ; 
2,  lacrimal  sac ;  3,  nasal  duct ; 
4,  plica  semilunaris ;  5,  car- 
uncula  lacrimalis. 


598  THE  NERVOUS  SYSTEM. 

beneath  the  conjunctiva,  are  the  Meibomian  glands  (Fig.  371), 
thirty  in  number  on  the  upper,  and  fewer  on  the  lower  lid. 
Their  ducts  open  on  the  edges  of  the  lids,  and  their  secretion 
prevents  the  adhesion  of  the  lids  and  the  tears  from  running 
over  them  on  to  the  cheeks. 

The  Sense  of  Hearing.— The  ear  (Fig.  373),  the  organ  of 
hearing,  consists  of  three  subdivisions  :  (1)  External ;  (2)  middle  ; 
and  (3)  internal. 

External  Ear.— The  external  ear  consists  of  the  pinna  or  auricle, 
and  the  external  auditory  canal  or  meatus.  The  function  of  the 


FIG.  373.— Diagram  of  organ  of  hearing  of  left  side :  1,  the  pinna ;  2,  bottom  of 
concha;  2,  2',  meatus  externus;  3,  tympanum  ;  above  3,  the  chain  of  ossicles;  3', 
opening  into  the  mastoid  cells :  4,  Eustachian  tube ;  5,  meatus  internus.  containing 
the  facial  (uppermost)  and  auditory  nerves ;  6,  placed  on  the  vestibule  of  the  laby- 
rinth above  the  fenestra  ovalis ;  a,  apex  of  the  petrous  bone ;  b,  internal  carotid 
artery ;  c,  styloid  process ;  d,  facial  nerve,  issuing  from  the  stylomastoid  foramen  ; 
«,  mastoid  process;  /,  squamous  part  of  the  bone  (Quain,  after  Arnold). 

pinna  is  to  collect  the  sound-waves  and  direct  them  to  the  external 
auditory  canal,  which  they  traverse  to  reach  the  membrana  tym- 
pani.  In  some  animals,  such  as  the  horse,  the  auricles  are  very 
important,  enabling  the  animal  to  detect  the  direction  from  which 
sounds  come,  and  they  are  capable  of  considerable  movement ; 
but  in  man  they  are  not  so  important,  although  when  the  hearing 
is  defective  they  are  of  assistance.  That  they  are  not  essential  to 
hearing  is  shown  by  the  fact  that  when  removed,  hearing  is  not 
affected,  and  also  by  the  fact  that  in  birds,  where  they  are  absent, 
the  sense  of  hearing  is  well  marked. 


SENSE  OF  HEARING. 


599 


The  pinna  (Fig.  375)  is  composed  of  yellow  fibrocartilage 
covered  by  skin,  although  in  some  parts,  as  the  lobule,  the  cartilage 
is  absent.  It  is  attached  to  the  meatus  and  other  parts  by  liga- 
ments and  muscles. 


FIG.  374.— Semidiagrammatic  section  through  the  right  ear :  G,  external  audi- 
tory meatus ;  T,  membrana  tympani ;  P,  tympanic  cavity ;  o,  fenestra  ovalis ; 
r,  fenestra  rotunda ;  B,  semicircular  canal ;  S,  cochlea ;  Vt,  scala  vestibuli ;  Pt,  scala 
tympani  (Czermak). 

External  Auditory  Meatus. — This  canal,  extending  from  the 
pinna  to  the  membrana  tympani,  is  about  3.2  cm.  in  length,  the 
outer  1.3  cm.  being  of  cartilage,  except  at  the  upper  and  back 


Fossa  of  helix. 
Anthelix. 

Concha. 
Antitragus. 


Helix. 


f  Fossa  of  anthelix. 


Tragus. 


Lobule. 


FIG.  375. — External  ear. 


part,  where  its  place  is  taken  by  fibrous  membrane.  The  inner 
2  cm.  is  osseous.  The  entire  canal  is  lined  with  skin,  which  in 
the  cartilaginous  portion  of  the  canal  contains  sebaceous  and 
perspiratory  glands,  their  product  being  cerumen  or  ear-wax 
(p.  417).  The  skin  lining  the  meatus  also  contains  hair-follicles. 


600 


THE  NERVOUS  SYSTEM. 


Inasmuch  as  in  the  examination  of  the  ear  and  the  treatment 
of  its  diseases  it  is  necessary  to  introduce  an  aural  speculum  (Fig. 
377),  a  knowledge  of  the  direction  and  shape  of  the  canal  is  essen- 
tial. Its  greatest  diameter  is  at  the  external  orifice  and  is  vertical ; 


FIG.  376.— Muscles  of  the  auricle :  1,  attollens  aurem  ;  2,  attrahens  aurem ;  3, 
Tetrahens  aurem;  4,  helicis  major;  5,  helicis  minor;  6,  tragicus,  with  6',  its  acces- 
sory portion  ;  7,  an ti tragicus ;  a,  spine  of  helix;  b,  concha  (Testutj. 

its  smallest  diameter  is  in  the  middle.  At  the  tympanic  end  the 
greatest  diameter  is  horizontal.  The  direction  of  the  canal  is 
obliquely  forward,  inward,  and  downward.  Before  introducing 
the  speculum  the  helix  of  the  ear  is  raised  upward  and  backward 
so  as  to  straighten  the  canal  as  much  as  possible. 

Middle  Ear. — This  is  called  also  the  tympa- 
num (Fig.  378). 

Membrana  Tympani  (Fig.  379). — This  mem- 
branous structure  separates  the  tympanic  cavity 
from  the  external  auditory  canal.  Its  shape  is 
oval,  and  the  direction  of  its  long  axis  is  down- 
ward and  inward  ;  its  diameter  along  this  axis 
is  about  9  mm.  It  is  composed  of  three  layers  : 
An  external  or  cuticular,  which  is  an  extension 
of  the  integument  that  lines  the  external  audi- 
f  j  I'll  tory  canal ;  an  internal,  mucous,  a  continuation 

of  the  mucous  membrane  lining  the  tympanic 
cavity  ;  and  a  middle,  fibrous,  made  up  of  both 
fibrous  and  elastic  tissues.  There  are  two  vari- 
eties of  these  fibers — radiating,  which  radiate  from  the  center  to 
the  circumference ;  and  circular,  which  form  a  ring  at  the  circum- 
ference. The  membrana  tympani  is  set  into  a  groove  in  a  ring 
of  bone,  except  at  the  upper  part,  where  it  is  attached  to  the  wall 
of  the  canal.  This  portion  of  the  membrane  is  not  so  tense  as 


FiG.  377.-Aural 
speculum. 


SENSE  OF  HEARING. 


601 


.»& 


.{t  F       ^m 


FIG.  378. — Tympanum  of  left  ear,  with  ossicles  in  situ :  1,  suspensory  ligament 
of  malleus ;  2,  head  of  malleus ;  3,  epitympanic  region ;  4,  external  ligament  of 
malleus ;  5,  processus  longus  of  incus ;  6,  base  of  stapes ;  7,  processus  brevis  of  mal- 
leus; 8,  head  of  stapes;  9,  os  orbicular e ;  10,  manubrium ;  11,  Eustachian  tube;  12, 
external  auditory  meatus ;  13,  membrana  tympani ;  14,  lower  part  of  tympanum 
(Morris). 


FIG.  379. — Otoscopic  view  of  left  membrana  tympani :  1,  membrana  fiaccida :  2,  2', 
folds  bounding  the  former ;  3,  reflection  from  processus  brevis  of  malleus ;  4,  pro- 
cessus longus  of  incus  (occasionally  seen)  ;  5,  membrana  tympani ;  6,  umbo  and  end 
of  manubrium;  7,  pyramid  of  light  (Morris). 


602 


THE  NERVOUS  SYSTEM. 


the  rest,  and  has  therefore  received  the  name  membrana  flacdda. 
It  is  called  also  Shrapnett's  membrane. 

When  a  normal  membrana  tympani  is  viewed  through  an  aural 
speculum,  there  is  seen  a  triangular  spot  or  CQne  or  pyramid  of 
light,  whose  apex  is  at  the  end  of  the  manubrium  or  handle  of  the 
malleus,  and  whose  base  is  at  the  circumference.  The  membrane 
is  funnel-shaped,  with  the  concavity  toward  the  meatus,  at  the 
apex  being  attached  the  tip  of  the  manubrium,  and  at  this  point 
on  the  outer  surface  is  the  umbo  (Fig.  379). 

Tympanic  Cavity  (Fig.  378). — In  this  cavity,  which  is  situated 
in  the  petrous  portion  of  the  temporal  bone,  are  the  chains  of  bones, 
the  ossicles,  serving  as  a 
means  of  communication 
between  the  membrana 
tympani  and  the  internal  * 

ear.  It  communicates 
posteriorly  with  the  mas- 
toid  antrum  and  the  mas- 


orfaculc 


FIG.  380.— The  ossicles  of  the 
left  ear,  external  view  (enlarged) 
(after  Gray). 


FIG.  381.— Malleus  of  the  right  side :  A, 
anterior  face  ;  B,  internal  face ;  1,  capitulum 
or  head  of  malleus ;  2,  cervix  or  neck ;  3, 
processus  brevis;  4,  processus  gracilis;  5, 
manubrium ;  6,  grooved  articular  surface  for 
incus  ;  7,  tendon  of  musculus  tensor  tympani 
(after  Testut). 


toid  cells,  and  anteriorly  with  the  pharynx  by  means  of  the  Eusta- 
chian  tube.  Two  openings,  the  fenestra  ovalis  and  fenestra  rotunda, 
give  it  communication  with  the  internal  ear.  The  roof  of  the  tym- 
panic cavity,  the  tegmen,  is  a  very  thin  plate  of  bone,  the  only  struc- 
ture separating  this  cavity  from  that  in  which  lies  the  brain.  It  is 
on  account  of  this  slight  separation  that  inflammation  of  the  middle 
ear  sometimes  extends  to  the  brain.  The  tympanic  cavity  is  lined 
by  mucous  membrane,  which  is  covered  with  ciliated  epithelium 
except  over  the  ossicles  and  the  membrana  tympani. 

Ossicles  (Fig.  380).— These  are  three  in  number :  the  malleus, 
the  incus,  and  the  stapes. 

Malleus  (Fig.  381). — The  malleus  is  about  18  mm.  long,  and 
consists  of  head,  neck,  manubrium,  processus  gracilis,  and  processus 
brevis. 

The  head  has  a  general  surface  for  articulation  with  the  incus. 


SENSE  OF  HEARING. 


603 


The  manubrium  or  handle  is  attached  to  the  membrana  tympani. 
The  processus  gracilis  is  attached  to  the  Gasserian  fissure  by  bone 
and  ligament.  The  processus  brevis  presses  against  the  membrana 
flaccida,  and  its  location  is  visible  by  inspection  of  the  external 


FIG.  382.— The  incus  of  the  right  side:  A,  anterior  face;  B,  internal  face:  1, 
body  of  incus;  2,  processus  brevis;  3,  processus  longus;  4,  articular  surface  for  the 
malleus ;  5,  a  convex  tubercle,  processus  lenticularis,  for  articulation  with  stapes ;  6, 
rough  surface  for  attachment  of  the  ligament  of  the  incus  (after  Testut). 

surface  of  the  membrana  tympani,  through  which  it  shows  (Fig. 
379).     The  malleus  is  held  in  place  by  ligaments  (Fig.  384). 

Incus  (Fig.  381). — This  is  called  also  ambos  and  anvil-bone. 
The  body  is  characterized  by  the  presence  of  an  articular  surface 
for  articulation  with  the  malleus.  It  has  two  processes — processus 
brevis  and  processus  longus.  The  processus  brevis  is  attached  by 
ligament  to  the  margin  of  the  opening  that  leads  into  the  mastoid 
cells.  The  processus  longus  is  nearly  parallel  with  the  handle 


FIG.  383.— The  stapes:  1, 
base  ;  2,  anterior  crus ;  3,  pos- 
terior crus ;  4,  articulating 
surface  of  head  of  the  bone ; 
5,  cervix  or  neck  (after  Tes- 
tut). 


f 


FIG.  384.— Ligaments  of  the  ossicles  and 
their  axis  of  rotation.  The  figure  represents 
a  nearly  horizontal  section  of  the  tympanum, 
carried  through  the  heads  of  the  malleus  and 
incus :  M,  malleus ;  I,  incus ;  t,  articular  tooth 
of  incus  ;  Ig.a.  and  Ig.e,  external  ligament  of 
malleus;  Ig.inc,  ligament  of  the  incus;  the 
line  a-x  represents  the  axis  of  rotation  of  the 
two  ossicles  (from  Foster,  after  Testut). 


of  the  malleus  and  ends  in  a  round  projection,  os  orbicular e  or 
lenticular  process,  which  articulates  with  the  head  of  the  stapes. 
During  fetal  life  the  os  orbiculare  exists  as  a  separate  bone. 

Stapes  (Fig.  383). — This  bone  is  so  called  from  its  resemblance 


604  THE  NERVOUS  SYSTEM. 

to  a  stirrup.  It  consists  of  a  head,  which  articulates  with  the 
os  orbiculare ;  a  neck,  into  which  the  stapedius  muscle  is  inserted  ; 
and  two  crura,  which  are  connected  with  the  base,  this  being 
attached  by  ligamentous  tissue  so  as  to  close. the  fenestra  ovalis. 

Ligaments  of  the  Ossicles. — The  ossicles  are  connected  with  one 
another,  and  also  with  the  walls  of  the  tympanum,  by  ligaments 
(Fig.  384).  One  of  these,  the  anterior  ligament  of  the  malleus, 
was  at  one  time  supposed  to  be  a  muscle  and  was  described  under 
the  name  levator  tympani. 

Muscles  of  the  Ossicles. — These  are  two  in  number — tensor 
tympani  and  stapedius. 

Tensor  Tympani. — This  muscle  lies  in  a  bony  canal  which 
is  above  the  canal  containing  the  Eustachian  tube,  and  sepa- 
rated from  it  by  the  processus  cochleariformis,  a  thin  plate  of 
bone.  It  has  its  origin  from  the  petrous  bone,  the  cartilaginous 
portion  of  the  Eustachian  tube,  and  the  bony  canal  in  which  it 
lies.  Its  tendon  enters  the  tympanum  and  bends  at  almost  a 
right  angle  around  the  end  of  the  processus  cochleariformis,  and 
is  inserted  into  the  mauubrium  near  the  neck.  Its  nervous  supply 
is  a  branch  from  the  otic  ganglion.  When  this  muscle  contracts, 
the  membrana  tympani  is  drawn  inward  and  made  more  tense. 

Stapedius. — This  muscle  arises  from  the  interior  of  the  pyramid 
which  is  situated  just  behind  the  fenestra  ovalis,  and  just  below 
the  opening  of  the  mastoid  antrum,  and  its  tendon  passes  out 
at  an  opening  in  the  apex ;  it  is  inserted  into  the  neck  of  the 
stapes.  Authorities  do  not  agree  as  to  the  effect  of  the  contrac- 
tion of  this  muscle.  Gray  says  that  "it  draws  the  head  of 
the  stapes  backward,  and  thus  causes  the  base  of  the  bone  to 
rotate  on  a  vertical  axis  drawn  through  its  own  center ;  in  doing 
this  the  back  part  of  the  base  would  be  pressed  inward  toward 
the  vestibule,  while  the  fore  part  would  be  drawn  from  it.  It 
probably  compresses  the  contents  of  the  vestibule." 

Sewall,  in  the  American  Text-Book  of  Physiology,  says  :  "  Con- 
traction of  the  muscle  would  cause  a  slight  rotation  of  the  stapes 
round  a  vertical  axis,  so  that  the  hinder  part  of  the  foot  of  the 
ossicle  would  be  pressed  more  deeply  into  the  fenestra,  while  the 
remaining  portion  would  be  drawn  out  of  it.  Its  action  probably 
reduces  the  pressure  in  the  cavity  of  the  perilymph,  and  thus  is 
antagonistic  to  that  of  the  tensor  tympani."  The  nervous  supply 
of  this  muscle  is  the  tympanic  branch  of  the  facial,  which  reaches 
the  muscle  through  a  canal  in  the  pyramid  which  communicates 
with  the  aquseductus  Fallopii. 

Eustachian  Tube  (Fig.  385).— Through  this  channel  the  tym- 
panum is  in  communication  with  the  pharynx.  It  is  about  36  mm. 
in  length,  and  passes  downward,  forward,  and  inward.  It  begins 
in  the  lower  part  of  the  anterior  wall  of  the  tympanum,  and  is 
bony  for  about  12  mm.  It  then  becomes  cartilaginous,  and 


SENSE  OF  HEARING. 


605 


remains  so  throughout  the  rest  of  its  course.  It  is  lined  by 
mucous  membrane,  the  epithelium  of  which  is  ciliated.  The  direc- 
tion of  the  motion  of  these  cilia  is  from  the  tympanum  to  the 


mouth,  holding  the  nostrils  closed  with  the  thumb  and  finger,  and 
forcibly  blowing.  The  pharyngeal  opening  is  at  the  upper  lateral 
part  of  the  pharynx  behind  the  inferior  turbinated  bone.  There 


Portion  of  Elista 
chian  tube  fret 
from  glands. 


Cartilage 


Mucosa  of  the 
pharynx. 


Glands. 


Glands. -K- 


FIG.  385. — Cross-section  of  the  Eustachian  tube  with  its  surrounding  parts  ;  X  12 
(from  a  preparation  by  Professor  Eiidinger). 

is  a  band  of  muscular  tissue,  the  dilatator  tubce,  which  joins  the 
tensor  palati. 

Mastoid  Antrum. — This  is  a  cavity  which  opens  into  the  attic 
or  epitympanic  recess,  an  extension  upward  and  backward  of  the 
tympanic  cavity.  It  is  in  this  recess  that  the  head  of  the  malleus 
and  a  part  of  the  incus  are  situated.  The  antrum  communicates 
with  the  mastoid  cells  in  the  mastoid  process.  Antrum  and  cells 
are  lined  by  mucous  membrane  which  is  continuous  with  that  of 
the  tympanum.  This  extension  of  the  mucous  membrane  explains 
how  inflammation  of  the  middle  ear  may  extend  to  the  mastoid 
cells. 

Fenestra  Ovalis  (Fig.  386). — This  is  an  oval  opening  in  the 
internal  wall  of  the  tympanum  into  the  vestibule  of  the  internal 


606 


THE  NERVOUS  SYSTEM. 


ear,  and  is  closed  by  the  stapes,  an  annular  ligament  uniting  the 
bone  to  the  fenestra. 

Fenestra  Eotunda. — This  opening,  also  on  the  internal  wall  of 
the  tympanum,  leads  into  the  cochlea  of  the  internal  ear.     It  is 


FIG.  386.— Eight  bony  labyrinth,  viewed  from  outer  side:  the  figure  represents 
the  appearance  produced  by  removing  the  petrous  bone  down  to  the  denser  layer 
immediately  surrounding  the  labyrinth  :  1,  2,  3,  the  superior,  posterior,  and  external 
or  horizontal  semicircular  canals  ;  4,  5,  6,  the  ampullse  of  the  same ;  7,  the  vestibule ; 
8,  the  fenestra  ovalis  ;  9,  fenestra  rotunda ;  10,  first  turn  of  the  cochlea  ;  11,  second 
turn ;  12,  apex  (from  Quain.,  after  Sommerring). 


FIG.  387. — Interior  view  of  left  bony  labyrinth  after  removal  of  the  superior  and 
external  walls :  1,  2,  3,  the  superior,  posterior,  and  external  or  horizontal  semicir- 
cular canals ;  4,  fovea  hemi-elliptica ;  5,  fovea  hemispherica  ;  6,  common  opening  of 
the  superior  and  posterior  semicircular  canals ;  7,  opening  of  the  aqueduct  of  the 
vestibule ;  8,  opening  of  the  aqueduct  of  the  cochlea ;  9,  the  scala  vestibuli ;  10, 
scala  tympani ;  the  lamina  spiralis  separating  9  and  10  (from  Quain,  after  Som- 
merring). 

closed  by  the  membrana  tympani  secundaria,  which  is  made  up  of 
an  external  or  mucous  layer,  a  continuation  of  that  lining  the 
tympanum  ;  and  an  internal  or  serous,  a  continuation  of  that  lining 
the  cochlea ;  between  these  two  is  a  third  or  fibrous  layer.  Be- 


SENSE  OF  HEARING.  607 

tween  the  two  fenestra}  is  the  promontory,  a  prominence  caused  by 
the  projection  of  the  first  turn  of  the  cochlea. 

Internal  Ear  (Figs.  386,  387).— This  is  called  also  the  labyrinth. 
It  consists  of  a  bony  part,  the  osseous  labyrinth,  in  which  is  con- 
tained the  membranous  labyrinth. 

Osseous  Labyrinth. — This  is  made  up  of  three  parts :  The 
vestibule,  the  semicircular  canals,  and  the  cochlea,  all  of  which 
are  connecting  cavities  in  the  petrous  bone.  These  cavities  not 
only  communicate  with  one  another,  but  through  the  fenestra 
ovalis  and  fenestra  rotunda  the  osseous  labyrinth  is  in  communica- 
tion with  the  tympanum ;  and  through  the  meatus  auditorius 
internus  with  the  cranial  cavity. 

Vestibule. — This  cavity  is  at  the  inner  side  of  the  tympanum, 
and  opens  anteriorly  into  the  cochlea  and  posteriorly  into  the 
semicircular  canals.  It  is  about  5  mm.  in  diameter,  and  on  its 
outer  wall  communicates  with  the  tympanum  through  the  fenestra 
ovalis,  which  is  closed  by  the  stapes  and  its  annular  ligament. 
The  fovea  or  fossa  hemispherica  is  a  depression  on  the  anterior 
wall.  This  is  perforated  anteriorly,  forming  the  macula  cribrosa, 
and  through  these  perforations  the  auditory  nerves  pass  to  the 
saccule.  Behind  the  fovea  hemispherica  is  a  vertical  ridge,  the 
crista  vestibuli.  The  aquceductus  vestibuli  communicates  with  the 
vestibule  by  an  opening  at  the  posterior  part  of  the  inner  wall. 
Through  this  canal  pass  a  vein  and  the  ductus  endolymphaticus. 
The  fovea  or  fossa  hemi-elliptica  is  an  oval  depression  on  the  roof  of 
the  vestibule.  Between  it  and  the  fovea  hemispherica  is  the  crista 
vestibuli.  Posteriorly  the  semicircular  canals  open  into  the  vesti- 
bule, while  the  opening  into  the  cochlea,  apertura  scalce  vestibuli 
cochlece,  is  situated  anteriorly. 

Semicircular  Canals. — These  are  three  in  number,  situated 
behind  the  vestibule  and  above  it.  Each  has  a  diameter  of  about 
1.5  mm.,  except  at  one  end,  the  ampulla,  where  the  diameter 
is  2.5  mm.,  and  each  canal  is  so  arranged  as  to  be  at  right  angles 
to  the  others.  The  superior  is  vertical  and  at  right  angles  to 
the  posterior  surface  of  the  petrous  bone  ;  its  ampullated  extremity 
opens  into  the  vestibule,  while  its  other  extremity  joins  with  the 
non-ampullated  extremity  of  the  posterior  canal,  and  these  open 
into  the  vestibule  by  one  common  opening.  The  posterior  canal  is 
also  vertical,  but  parallel  with  the  posterior  suriace  of  the  petrous 
bone.  Its  ampullated  extremity  opens  into  the  vestibule.  The 
external  canal  is  horizontal,  and  both  its  extremities  open  into  the 
vestibule.  It  will  be  seen  that  the  three  canals  have  but  five 
openings  into  the  vestibule,  one  opening  being  common  to  two 
canals. 

Cochlea  (Fig.  388).— The  cochlea  is  situated  in  front  of  the 
vestibule,  with  its  apex  directed  outward,  forward,  and  downward, 
its  base  corresponding  to  the  internal  auditory  meatus.  It  is  5 


608  THE  NERVOUS  SYSTEM. 

mm,  long  and  9  mm.  broad  at  its  base.  It  consists  of  an  axis, 
the  modiolus  or  columella,  which  runs  through  the  entire  structure, 
from  the  base  to  the  apex ;  around  the  modiolus  runs  the  spiral 
canal.  At  the  base  the  raodiolus  is  perforated  to  transmit  filaments 
of  the  cochlear  branch  of  the  auditory  nerve,  and  through  it  ex- 
tends the  canalis  centralis  modioli,  which  transmits  a  nerve  and  an 
artery. 

The  spiral  canal  is  about  2  mm.  in  diameter  and  3.3  cm.  in 
length.     It  makes  two   and  three-fourth  turns,  clockwise — i.  e., 


FIG.  388.— The  cochlea  and  vestibule  as  seen  from  above:  A,  cochlea;  B,  vesti- 
bule ;  (7,  internal  auditory  canal ;  D,  tympanum.  1,  Lower  border  of  fenestra  ovalis ; 
2,  vestibulotympanic  cleft;  3,  fossa  hemispherica ;  4,  fossa  hemi-elliptica ;  5,  fossa 
cochlearis ;  6,  orifice  of  aqueduct  of  vestibule ;  7,  lower  orifice  of  posterior  semi- 
circular canal ;  8,  non-amp  ullary  orifice  of  the  external  semicircular  canal ;  9,  scala 
tympani ;  10,  scala  vestibuli ;  11,  cupola  ;  12,  lamina  spiralis,  with  12',  its  vestibulary 
origin ;  12",  its  external  border  ;  13,  helicotrema  (Testut). 

in  the  direction  taken  by  the  hands  of  a  clock — around  the 
modiolus.  At  the  apex  the  canal  terminates  in  the  cupola.  This 
canal  is  partially  divided  into  two  by  a  bony  septum,  the  lamina 
spiralis,  which  consists  of  two  thin  plates  of  bone  between  which 
are  minute  canals  for  the  transmission  of  nerve-fibers.  The 
lamina  spiralis  extends  from  the  modiolus  only  about  half-way 
toward  the  outer  wall  of  the  spiral  canal.  In  the  recent  state 
there  is  a  membrane,  the  membrana  basilaris,  extending  from  the 
edge  of  the  lamina  spiralis  to  the  outer  wall,  dividing  the  canal 
into  two  parts,  the  lower  being  the  scala  tympani,  while  the 


SENSE  OF  HEARING.  609 

upper  is  again  subdivided  by  a  membrane,  the  membrane  ofReissner, 
into  two  canals :  that  between  the  inner  wall  of  the  cochlea  and 
this  membrane  being  the  scala  vestibuli;  and  that  between  the 
outer  wall  and  the  membrane  of  Reissner,  having  the  membrana 
basilaris  as  its  base,  the  scala  media,  ductus  cochlece,  or  canalis 
cochlece.  This  latter  is  in  reality  a  part  of  the  membranous 
labyrinth,  not  of  the  osseous,  but  it  is  somewhat  more  convenient 
to  describe  it  at  this  point.  At  the  apex  of  the  cochlea  the 
lamina  spiralis  ends  in  the  hamulas,  a  hook-like  process,  and  here 
the  scala  vestibuli  and  scala  tympani  communicate,  the  opening 
being  the  helicotrema.  At  the  junction  of  the  lamina  spiralis  and 
the  modiolus,  and  winding  around  the  latter,  is  the  canalis  spiralis 
modioli,  which  lodges  the  ganglion  spirale,  an  enlargement  of  the 
cochlear  nerve  containing  ganglion-cells.  From  this  are  given 
off  the  nerves  to  the  organ  of  Corti. 

The  scala  vestibuli  communicate,s  with  the  vestibule  at  its 
lower  end.  The  scala  tympani  at  its  lower  end  terminates  at  the 
fenestra  rotunda,  which  is  closed  by  the  membrana  tympani 
secundaria. 

Aquceductus  Cochlece. — This  is  a  small  canal  running  from  the 
scala  tympani  to  the  basilar  surface,  of  the  petrous  bone  which 
transmits  a  vein  from  the  cochlea  that  joins  the  internal  jugular 
vein. 

Lining  of  Osseous  Labyrinth. — All  the  cavities  of  the  osseous 
labyrinth  are  lined  by  a  fibroserous  membrane,  regarded  by  some 
as  periosteum ;  this  membrane  also  covers  the  fenestra  ovalis 
and  fenestra  rotunda.  On  its  inner  surface  is  a  layer  of  epithe- 
lium which  secretes  the  perilymph,  a  watery  fluid  containing 
niucin,  which  fills  so  much  of  the  osseous  labyrinth  as  is  not 
occupied  by  the  membranous  labyrinth. 

Membranous  Labyrinth  (Fig.  391). — The  membranous  labyrinth 
is  contained  within  the  osseous,  and  is,  to  a  certain  extent,  a  dupli- 
cation of  it.  Its  walls  consist  of  three  layers  :  ] .  An  external, 
which  is  made  up  of  fibrous  tissue,  rather  loose  in  structure,  in 
which  are  blood-vessels  and  pigment-cells  similar  to  those  in  the 
retinal  pigmentary  layer  ;  2.  A  middle  layer,  thicker  than  the 
external,  and  somewhat  like  the  hyaloid  membrane  of  the  eye ; 
and  3.  An  internal,  composed  of  polygonal  nucleated  epithelium 
which  secretes  the  endolymph  or  liquor  Scarpce,  a  fluid  similar  in 
composition  to  the  perilymph,  and  contained  within  the  membra- 
nous labyrinth,  as  the  perilymph  is  within  the  osseous. 

The  membranous  labyrinth  consists  of  the  utricle  and  saccule, 
which  are  contained  in  the  vestibule ;  the  three  membranous  semi- 
circular canals,  and  the  canal  of  the  cochlea  or  scala  media. 

The  utricle,  saccule,  and  membranous  semicircular  canals  are 
attached  on  one  side  to  the  wall  of  the  osseous  labyrinth,  and  from 
the  opposite  side  are  given  off  bands  of  fibrous  tissue  which  hold 

39 


610  THE  NERVOUS  SYSTEM. 

them  to  the  corresponding  wall  of  the  osseous  labyrinth.  In  these 
bands  are  the  blood-vessels  and  the  fibers  of  the  auditory  nerve 
which  are  distributed  to  the  utricle,  saccule,  and  membranous 
semicircular  canals. 

Utricle. — The  utricle  or  utriculus  is  situated  in  the  upper  and  back 
part  of  the  vestibule  at  the  fovea  hemi-elliptica,  and  is  oblong  in 
shape.  It  communicates  posteriorly  with  the  membranous  semi- 
circular canals  by  five  openings,  and  from  it  passes  a  small  canal 
which  unites  with  one  from  the  saccule,  the  two  forming  the  ductus 
endolymphaticus.  Branches  of  the  auditory  nerve  pierce  the  wall 
of  the  utricle  at  one  point,  and  here  the  tunica  propria  is  thick- 
ened, and  the  epithelium  consists  of  columnar  cells  upon  which 
are  long,  stiff",  tapering  hairs,  around  which  the  axis-cylinders 
of  the  auditory  nerve-fibers  ramify.  Schafer,  to  Whom  we  are 
indebted  for  this  description,  says  that  these  are  like  the  rod- 
and  cone-elements  of  the  retina,  the  bipolar  cells  of  the  olfactory 
membrane,  and  the  gustatory  cells  of  the  taste-buds — sensory  or 
nerve-epithelium  cells.  Between  the  hairs  are  nucleated  cells, 


FIG.  389.— Section  of  macula  of  utricle,  human :  n.  utr.,  bundles  of  the  utricular 
branch  of  the  eighth  nerve;  h,  auditory  hairs;  p.l.s.,  perilymphatic  space  (G. 
Betzius). 

fiber-cells  of  Retzius,  which  rest  upon  the  basement-membrane, 
and  are  connected  at  their  free  extremity  with  a  cuticular  mem- 
brane through  which  the  auditory  hairs  project.  The  auditory 
hairs  do  not  project  free  into  the  endolymph,  but  into  a  soft, 
mucus-like  substance  of  a  dome-like  form  in  the  ampullae,  and 
which  in  the  saccule  and  utricle  has  a  mass  of  calcareous  particles, 
otoliths,  embedded  in  it.  The  otoliths  are  also  called  otoconia  and 
ear-stones,  and  are  minute  crystals  of  calcium  carbonate.  The 
thickening  of  the  tunica  propria  with  the  modified  cells,  etc.,  just 
described,  forms  the  macula  acustica  in  the  utricle  and  saccule 
(Figs.  389,  390).  In  the  ampullae  of  the  semicircular  canals  the 
columnar  cells  and  auditory  hairs  are  upon  a  ridge,  and  here 
the  structure  is  called  crista  acustica.  The  cristse  of  the  ampullae 
have  essentially  the  same  structure  as  the  maculae  of  the  utricle 
and  saccule,  save  that  the  otoliths  are  absent. 

Saccule. — The  saccule  or  sacculus  is  globular,  smaller  than  the 
utricle,  being  about  3  mm.  by  2  mm.  in  diameter,  and  lies  in  the 
fovea  hemispherica.  It  receives  nervous  filaments  derived  from 


SENSE  OF  HEARING. 


611 


the  auditory  nerve,  which  terminate,  as  already  described,  in  a 
macula  acustica  in  which  are  otoliths,  and  it  gives  off  a  small 
canal  which,  uniting  with  that  coming  from  the  utricle,  forms  the 


FIG.  390.— Nerve  terminations  in  macula  ;  Golgi  method  (G.  Retzius). 

ductus  endolymphaticus.     On  the  opposite  side  is  a  similar  canal, 
1  mm.  long  and  0.5  mm.  wide,  the  canalis  reuniens  (Fig.  391),  by 


FIG.  391. — Diagram  of  right  membranous  labyrinth  seen  from  the  external  side  : 
1,  utricle;  2,  3,  4,  superior,  posterior,  and  horizontal  semicircular  canals;  5,  saccule; 
6,  ductus  endolymphaticus,  with  7,  7',  its  twigs  of  origin  ;  8,  saccus  endolymphaticus  ; 

9,  canalis  cochlearis,  with  9',  its  vestibular  cul-de-sac,  and  9",  its  blind  extremity; 

10,  canalis  reuniens  (after  Testut). 

which  it  is  in  communication  with  the   scala   media  or  canalis 
cochlearis. 

Ductus  Endolymphaticus. — This  canal,  formed  by  the  union  of 
the  canals  from  the  utricle  and  saccule,  is  lodged  in  the  aquseducttis 


612 


THE  NERVOUS  SYSTEM. 


vestibuli.  It  terminates  in  a  dilated  and  flattened  cul-de-sac, 
which  lies  within  the  cranial  cavity  between  the  layers  of  the 
dura  mater. 

Membranous  Semicircular  Canals. — These  are  three  in  number, 
in  shape  like  the  osseous  canals,  but  are  only  about  one-third  their 
diameter ;  they  open  by  five  apertures  into  the  utricle.  The  lining 
of  the  canals  forms  papilliform  elevations  (Fig.  392).  In  each 
ampulla  is  the  ridge,  crista  acustica,  already  described  (p.  610). 


Membranous  semicircular  canal. 


Blood-vessel. 


Wall  of  mem- 
branous 
canal. 


Epithelium  of  the 
membranous 
canal. 


Ligament  of 
canal. 


Bone. 


Perilymphatic    V 

spaces. 


Blood-vessel. 

FIG.  392. — Transverse  section  through  an  osseous  and  membranous  semicircular 
canal  of  an  adult  human  being :  a,  connective-tissue  strand  representing  a  remnant 
of  the  embryonic  gelatinous  connective  tissue.  Such  strands  serve  to  connect  the 
membranous  canal  with  the  osseous  wall ;  X  50  (after  a  preparation  by  Dr.  Scheibe) 
(Bohm  and  Davidoff ). 

Canal  of  the  Cochlea. — For  the  following  description  we  are 
indebted  to  Schafer's  Essentials  of  Histology:  "The  periosteum, 
a  peculiar  kind  of  connective  tissue  which  covers  the  upper  surface 
of  the  lamina  spiralis,  is  thickened,  forming  the  limbus,  also  called 
limbus  lamince  spiralis,  and  denticulate  lamina  by  Todd  and  Bow- 
man, and  the  edge  is  grooved,  somewhat  resembling  the  letter  C, 
the  upper  part  of  which  is  the  labium  tympanieum  ;  between  these 
labia  is  the  sulcus  spiralis  (Fig.  393).  The  membrana  basilaris, 
already  referred  to  (p.  608),  extends  from  the  labium  tympanieum 


SENSE  OF  HEARING. 


613 


to  the  outer  bony  wall  of  the  cochlea,  where  it  is  enlarged,  forming 
the  ligamentum  spirale.  From  the  base  of  the  labium  vestibulare 
a  membrane  (Reissner's  membrane)  extends  to  the  outer  wall,  above 
and  nearly  parallel  with  the  membrana  basilaris.  Between  this 
membrane  and  the  membrana  basilaris  is  the  ductus  cochlearis  or 
ductus  auditorius,  and  in  this,  situated  upon  the  membrana  basilaris, 


FIG.  393. — Section  through  one  of  the  turns  of  the  osseous  and  membranous 
cochlear  ducts  of  the  cochlea  of  a  guinea-pig :  I,  scala  vestibuli ;  m,  labium  vestibu- 
lare of  the  limbus ;  n,  sulcus  spiralis  internus ;  o,  nerve-fibers  lying  in  the  lamina 
spiralis;  p,  ganglion -cells ;  g,  blood-vessels;  «,  bone;  6,  Eeissner's  membrane;  DC, 
ductus  cochlearis;  d,  Corti's  membrane;  /,  prominentia  spiralis;  <7,  organ  of  Corti : 
ft,  ligamentum  spirale ;  i,  crista  basilaris ;  fc,  scala  tympani ;  X  90  (Bohm  and 
Davidoff). 

is  the  organ  of  Corti.  The  membraua  basilaris  is  composed  of  stiff, 
straight  fibers,  estimated  at  24,000  in  number,  which  are  embedded 
in  a  homogeneous  stratum.  It  is  much  broader  in  the  uppermost 
turns  of  the  cochlea  than  in  the  lowest ;  the  width  being  at  the 
bottom,  0.21  mm. ;  in  the  middle,  0.34  mm. ;  and  at  the  top, 
0.36  mm." 


THE  NERVOUS  SYSTEM. 

Organ  of  Corti  (Figs.  394,  395).— This  consists  of  (1)  the 
rods  of  Corti ;  (2)  a  reticular  lamina ;  (3)  outer  hair-cells ;  (4) 
inner  hair-cells. 


V    t'  n*'  * 


FIG.  394.— Organ  of  Corti :  at  x  the  tectorial  membrane  is  raised  ;  e,  outer  sus- 
tentacular  cells ;  d,  outer  auditory  cells ;  /,  outer  pillar  cells :  g,  tectorial  membrane ; 
h,  inner  sustentacular  cells;  i,p,  epithelium  of  the  sulcus  spiralis  internus;  k,  labium 
vestibulare ;  e,  tympanic  investing  layer ;  m,  outer  auditory  cells ;  n,  n,  nerve-fibers 
which  extend  through  the  tunnel  of  Corti  ;  o,  inner  pillar  cell;  q,  nerve-fibers;  6,  6, 
basilar  membrane ;  a,  epithelium  of  the  sulcus  spiralis  externus ;  r,  cells  of  Hensen ; 
s,  inner  auditory  cell ;  I,  ligamentum  spirale  (after  Eetzius). 

Rods  of  Corti. — These  are  of  two  kinds,  the  inner,  of  which 
there  are  5600,  and  the  outer,  3850  in  number.  They  are  both 


FIG.  395.— Section  of  Corti's  organ  from  guinea-pig's  cochlea :  8T,  scala  tympani  : 
TC,  tunnel  of  Corti ;  a,  bony  tissue  or  spiral  lamina ;  6,  6,  fibrous  tissue  covering 
same  continued  as  substantia  propria  of  basilar  membrane ;  c,  c,  protoplasmic  envelope 
of  Corti's  pillars  (e,  e)  •  d,  endothelial  plates ;  /,  heads  of  pillars  containing  oval 
areas ;  g,  head  plates  of  pillars ;  h,  h',  inner  and  outer  hair-cells ;  m,  membrana 
reticularis ;  fc,  I,  cells  of  Hensen  and  Claudius ;  n,  n,  nerve-fibers ;  L  cells  of  Deiters 
(after  Piersol). 

stiff,  striated  cells ;  the  shape  of  the  inner  has  been  compared  to 
that  of  the  human  ulna,  with  a  depression  like  the  sigmoid  cavity 
and  processes  like  the  coronoid  and  olecranon ;  the  shape  of  the 


SENSE  OF  HEARING.  615 

outer,  to  the  head  and  neck  of  a  swan.  The  feet  of  the  rods 
rest  on  the  basilar  membrane,  and  here  may  be  seen  the  cells 
from  which  they  are  derived ;  their  heads  are  joined  together, 
the  head  of  the  outer  fitting  into  the  depression  of  the  inner. 
Inasmuch  as  the  rods  are  arranged  in  a  series  by  the  side  of  one 
another,  this  arrangement  makes  a  tunnel,  the  floor  of  which  is  the 
basilar  membrane,  while  the  sloping  sides  are  made  by  the  inclined 
rods.  From  each  outer  rod  projects  a  phalangeal  process. 

Reticular  Lamina. — This  is  also  described  under  the  name 
membrane  of  Kolliker,  and  consists  of  a  network  in  which  are 
perforations.  It  is  made  up  of  u  minute  fiddle-shaped  cuticular 
structures,"  phalanges,  and  through  the  perforations  which  are 
between  these  phalanges  project  the  cilia  of  the  outer  hair-cells. 

Outer  Hair-cells. — These  are  12,000  in  number,  and  are 
arranged  in  three  or  four  rows  external  to  the  outer  rods,  each 
cell  being  surmounted  by  a  bundle  of  short  auditory  hairs  which 
projects  through  one  of  the  perforations  of  the  reticular  lamina. 
From  the. other  extremity  is  given  off  a  fine  process  which  is 
attached  to  the  membrana  basilaris.  Between  the  rows  of  hair- 
cells  are  the  cells  of  Deitws,  regarded  as  supporting  cells,  with 
their  bases  on  the  membrana  basilaris  and  their  tapering  processes 
attached  to  the  reticular  lamina. 

Inner  Hair-cells. — These,  3500  in  number,  are  arranged  in  a 
single  row,  internal  to  the  internal  rods,  and,  like  the  outer  hair- 
cells,  possess  auditory  hairs.  The  epithelial  cells  next  to  the 
outer  hair-cells  are  long  and  columnar,  but  cubical  over  the  outer 
wall  of  the  canal  of  the  cochlea ;  they  are  much  the  same  on  the 
inner  side  of  the  inner  hair-cells,  but  are  of  the  pavement 
variety  on  the  membrane  of  Reissner. 

Membrana  Tectoria. — This  structure,  called  also  the  membrane 
of  Corti,  is  soft  and  fibrillated.  It  extends  from  the  limbus,  and 
"  lies  like  a  pad  over  the  organ  of  Corti,"  probably  resting  on  the 
auditory  hairs.  Retzius  states  that  it  is  attached  to  the  reticular 
lamina.  Gray  says  that  it  is  blended  with  the  ligamentum  spirale 
on  the  outer  wall  of  the  spiral  canal. 

Auditory  Nerve. — The  auditory  nerve  divides  into  two  branches 
at  the  bottom  of  the  meatus  auditorius  internus ;  these  are  the 
cochlear  and  vestibular. 

Cochlear  Branch  of  Auditoi*y  Nerve. — This  is  called  also 
cochlear  nerve.  At  the  base  of  the  columella  or  modiolus  of  the 
cochlea  it  subdivides  into  filaments,  which  run  through  it  in 
canals.  When  they  reach  the  lamina  spiralis  they  form  at  its 
base  the  ganglion  spirale,  composed  of  a  plexus  of  the  nervous 
filaments  with  ganglion-cells.  From  the  ganglion  spirale  delicate 
filaments  are  given  off,  which  pass  between  the  plates  of  the 
lamina  spiralis  until  they  reach  the  sulcus  spiralis,  where  they  pass 
out  to  the  organ  of  Corti.  Waldeyer  states  that  here  they  divide 


616  THE  NERVOUS  SYSTEM. 

into  two  groups — one  going  to  the  inner  hair-cells,  the  other  to 
the  outer.  Schafer  says  that  "  after  traversing  the  spiral  lamina 
they  emerge  in  bundles,  and  the  fibers  then,  having  lost  their 
medullary  sheath,  pass  into  the  epithelium  of  the  inner  hair-cell 
region.  Here  some  of  them  course  at  right  angles,  and  are 
directly  applied  to  the  inner  hair-cells,  whilst  others  cross  the 
tunnel  of  Corti,  to  become  applied  in  like  manner  to  the  outer 
hair-cells  and  the  cells  of  Deiters ;  but  there  does  not  appear  to 
be  any  continuity  between  the  nerve-fibrils  and  the  cell-substance." 

Vestibular  Branch  of  Auditory  Nerve. — This  is  often  spoken  of 
as  the  vestibular  nerve.  It  divides  into  three  branches :  1,  supe- 
rior,  which  is  distributed  to  the  utricle  and  the  ampullae  of  the 
external  and  superior  semicircular  canal ;  2,  middle,  which  is  dis- 
tributed to  the  saccule ;  and  3,  inferior,  which  is  distributed  to 
the  ampulla  of  the  posterior  semicircular  canal. 

Physiology  of  Hearing. — Sound  is  defined  by  the  Standard 
Dictionary  as  :  "1.  The  sensation  produced  through  the  organs  of 
hearing.  2.  The  physical  cause  of  this  sensation  ;  waves  of  alter- 
nate condensation  and  rarefaction  passing  through  an  elastic  body, 
whether  solid,  liquid,  or  gaseous,  but  especially  through  the  atmo- 
sphere." 

Bodies  which  emit  sound  are  called  sonorous  bodies,  and  are  at 
the  time  in  a  state  of  vibration.  Thus  a  tuning-fork  when  set  in 
vibration  produces  in  the  air  around  it  a  series  of  condensations 
and  rarefactions  which  form  "  concentric  spherical  shells  of  air  of 
different  densities.  Each  air  particle  swings  to  and  fro  in  a  very 
short  path  along  the  radius  of  the  sphere — that  is,  the  vibrations 
are  longitudinal "  (Carhart  and  Chute). 

These  waves  are  sound-waves,  and  when  they  enter  the  external 
auditory  meatus  they  set  up  vibrations  in  the  membrana  tympani. 
.  Through  the  ossicles  these  vibrations  are  transmitted  to  the  peri- 
lymph.  The  base  of  the  stapes,  which,  with  its  annular  membrane, 
closes  the  fenestra  ovalis,  communicates  these  vibrations  to  the 
perilymph  in  the  scala  vestibuli,  along  which  waves  of  the  fluid 
travel,  passing  through  the  helicotrema  and  down  the  scala 
tympani  to  the  fenestra  rotunda,  the  membrana  tympani  secun- 
daria  being  pressed  out  as  each  wave  reaches  it.  In  this  course 
the  waves  of  perilymph  pass  over  the  membrane  of  Reissner  as 
they  travel  up  the  scala  vestibuli,  and  under  the  membrana 
basilaris  as  they  return  down  the  scala  tympani,  thus  setting  up 
corresponding  vibrations  in  the  endolymph  which  fills  the  membra- 
nous cochlea. 

The  external  ear  collects  the  sound-waves,  and  in  some  animals, 
as  in  the  horse,  is  very  useful  in  determining  the  direction  from 
which  sounds  come  ;  these  animals,  by  virtue  of  muscles  attached 
to  the  ear,  can  move  it  in  all  directions.  In  man  such  muscles 
exist,  but  in  a  relatively  undeveloped  form,  and  are  not  under  the 


SENSE  OF  HEARING.  617 

control  of  the  will  to  any  extent,  although  some  individuals  can 
produce  a  slight  to-and-fro  motion  of  the  auricle.  When  the 
hearing  is  imperfect  the  hand  is  sometimes  applied  to  the  ear  in 
such  manner  as  to  increase  its  projection  from  the  side  of  the  head 
and  to  supplement  it,  so  as  to  collect  more  sound-waves  than 
would  otherwise  enter  the  meatus. 

In  order  that  the  membrana  tympani  should  respond  to  the 
many  tones  and  shades  of  tones  which  reach  it,  it  is  important  that 
the  pressure  upon  the  internal  and  external  surfaces  should  be  the 
same,  and  this  is  effected  by  the  passage  of  air  through  the  Eus- 
tachian  tube,  so  that  in  going  from  an  atmosphere  of  one  density 
into  that  of  another  the  equilibrium  is  thus  maintained.  The 
pharyngeal  aperture  of  the  tube,  ordinarily  closed,  is  opened  by 
the  action  of  the  tensor  palati  at  each  act  of  swallowing. 

When  the  membrana  tympani  moves  inward,  the  manubrium 
of  the  malleus  moves  inward  also,  and  with  it  the  incus,  the 
articulation  between  these  two  ossicles  being  such  that  in  tjiis  in- 
ward movement  they  move  as  one.  In  speaking  of  this  articula- 
tion Helinholtz  says  :  "  In  its  action  it  may  be  compared  with  the 
joints  of  the  well-known  Breguet  watch-keys,  which  have  rows  of 
interlocking  teeth,  offering  scarcely  any  resistance  to  revolution  in 
one  direction,  but  allowing  no  revolution  whatever  in  the  other/' 
When  the  membrana  tympani  is  forced  strongly  outward,  the  manu- 
brium glides  in  the  joint,  and  the  incus  follows  it  for  but  a  short 
distance ;  if  this  was  not  so,  in  such  movements  of  the  membrana 
tympani  the  stapes  would  be  pulled  out  of  the  fenestra  ovalis,  and 
severe,  if  not  irretrievable,  injury  would  result.  This  extreme 
outward  movement  of  the  membrana  tympani  might  result  from 
increased  pressure  within  the  tympanum  or  diminished  pressure 
in  the  external -auditory  meatus.  These  movements  of  the  drum- 
membrane  and  the  stapes  are  at  most  but  limited ;  the  maximum 
for  the  membrane  being  only  from  y1^  to  ^  mm.,  and  of  the  stapes 
from  about  ^  to  ^  mm.  The  amplitude  of  movement  of  the 
latter  may  be  only  Y^STF  mm- 

Thus  is  accomplished  the  conversion  of  sound-waves  into 
waves  of  perilymph.  Helmholtz  says  :  "  The  mechanical  problem 
which  the  apparatus  within  the  drum  of  the  ear  had  to  solve  was 
to  transform  a  motion  of  great  amplitude  and  little  force,  such  as 
impinges  on  the  drum-skin,  into  a  motion  of  small  amplitude  and 
great  force,  such  as  had  to  be  communicated  to  the  fluid  in  the 
labyrinth."  A  study  of  the  ossicles  (Fig.  396)  shows  that  their 
movement  is  around  the  axis  of  rotation,  a-x  in  Fig.  397.  If  the 
distance  from  this  axis  to  the  tip  of  the  manubrium  is  measured, 
it  will  be  found  to  be  one  and  one-half  times  that  from  the  axis 
to  the  end  of  the  long  process  of  the  incus,  with  which  the  stapes 
articulates,  so  that  the  amplitude  of  the  movement  of  the  stapes 


618 


THE  NERVOUS  SYSTEM. 


will  be  but  two-thirds  that  of  the  tip  of 'the  manubrium,  but  will 
have  one  and  one-half  times  its  force. 

The  action  of  the  tensor  tympani  and  that  of  the  stapedius 
have  been  already  described  (p.  604). 

It  is  interesting  to  note  that  sound  may  be*  conducted  to  the  in- 
ternal ear  through  the  bones  of  the  skull  so  as  to  cause  the  sensa- 
tion of  hearing.  Thus  if  a  vibrating  body,  as  a  tuning-fork,  is  held 
between  the  teeth,  it  can  be  heard  though  the  ears  are  closed  ; 
indeed,  it  sounds  more  loudly  when  the  ears  are  closed  than  when 
they  are  open.  The  sound  is  conducted  by  the  bones  to  the 
internal  ear,  and  also,  doubtless,  some  of  the  sound  is  due  to 
vibrations  of  the  membrana  tympani. 

This  fact  is  made  use  of  in  the  audiphone,  a  fan-like  device 
held  in  the  teeth  by  the  deaf.  If  the  essential  portions  of  the 
auditory  apparatus  are  so  diseased  as  to  cause  deafness,  no  such 
device  as  the  audiphone  will  be  of  any  use. 

Tlveories  of  Hearing. — Two  theories   have   been  advanced   to 


FIG.  396.— The  chain  of 
auditory  ossicles,  anterior 
view:  1,  head  of  malleus; 
2,  long  process  of  incus;  3, 
stapes  (after  Testut). 


FIG.  397. — Ligaments  of  the  ossicles  and 
their  axis  of  rotation.  The  figure  represents 
a  nearly  horizontal  section  of  the  tympanum, 
carried  through  the  heads  of  the  malleus  and 
incus :  M,  malleus ;  /,  incus ;  t,  articular  tooth 
of  incus  ;  Ig.a.  and  Ig.e,  external  ligament  of 
malleus;  Ig.inc,  ligament  of  the  incus;  the 
line  a-x  represents  the  axis  of  rotation  of  the 
two  ossicles  (from  Foster,  after  Testut). 


explain  the  physiology  of  hearing :  (1)  The  piano  theory  and  (2) 
the  telephone  theory. 

The  Piano  Theory. — This  is  by  far  the  older,  and  may  be 
'regarded  as  the  theory  usually  held  to  explain  what  takes  place  in 
the  cochlea.  The  cochlear  division  of  the  auditory  nerve  sends 
into  the  modiolus  of  the  cochlea  branches  that  pass  in  between  the 
plates  of  the  lamina  spiralis,  where  they  form  a  plexus  in  which 
are  ganglion-cells,  from  which  the  nerve-filaments  pass  to  the 
organ  of  Corti,  terminating,  it  is  believed,  in  the  hair-cells. 

The  waves  already  referred  to  as  being  set  in  motion  in  the 
endolymph  pass  over  and  under  these  cells,  with  which  the  nerve- 
filaments  are  connected,  and  cause  the  basilar  membrane  on  which 
they  rest  to  vibrate.  This  motion  is  communicated  to  the  outer 
rods  of  Corti,  which  in  turn  pass  it  to  the  hairs  of  the  special  audi- 
tory cells  through  the  medium  of  the  perforated  membrane,  and  from 


SENSE  OF  HEARING.  619 

there  it  passes  to  the  nerves.  Here  it  is  converted  into  impulses 
which  are  transmitted  to  the  brain,  where  sound  is  produced. 

It  has  been  supposed  that  the  rods  of  Corti  are  so  arranged  as 
to  vibrate  with  particular  tones,  one  rod  for  each  tone,  but  it  is 
doubtful  whether  such  a  differentiation  can  be  made  out  in  the 
auditory  apparatus.  The  rods  are  not  present  in  the  ears  of  birds, 
and  there  is  no  reason  to  believe  that  birds  cannot  appreciate 
musical  tones.  In  the  basilar  membrane  there  are'  fibers  enough 
to  respond  to  all  the  notes  that  can  be  appreciated — that  is,  from 
33  waves  to  38,000  waves  in  a  second.  It  is  more  probable  that 
the  rods  simply  act  as  levers  to  communicate  the  vibrations  of 
the  fibers  of  the  basilar  membrane  to  the  terminal  nerve-filaments 
in  the  auditory  cells. 

Just  how  one  is  able  to  distinguish  the  differences  in  the  in- 
tensity (loudness),  pitch,  and  quality  of  sounds  is  not  understood. 
The  explanation  most  generally  accepted  at  the  present  time,  as 
to  pitch  at  least,  is  that  as  when  a  tone  is  sung  over  the  strings  of 
a  piano,  certain  strings  are  set  in  vibration  sympathetically,  so  in 
the  basilar  membrane,  where,  as  in  the  piano,  there  are  fibers  of 
different  lengths,  these  respond  to  different  tones,  and  that  in  con- 
nection with  each  tone  there  is  a  separate  filament  of  the  auditory 
nerve,  so  that  if  the  note  is  a  high  one  a  certain  fiber  is  set  in 
vibration,  and  the  nerve-filament  in  communication  with  it 
transmits  an  impulse  to  certain  cells  in  the  brain,  which  when 
excited  give  the  impression  of  a  high  note,  and  so  with  other 
notes  and  other  nerve-cells. 

The  Telephone  Theory. — The  introduction  of  the  telephone  and 
a  study  of  its  mechanism  have  led  some  writers  to  question  the 
explanation  which  is  generally  accepted  of  the  mechanism  of 
hearing,  and  to  suggest  that  as  the  single  telephone  wire  transmits 
the  complex  sounds  produced  by  an  orchestra  to  a  distance  where 
they  are  reproduced  in  all  their  variety  of  intensity,  pitch,  and 
quality,  so  "  the  cochlea  does  not  act  on  the  principle  of  sympa- 
thetic vibration,  but  that  the  hairs  of  all  its  auditory  cells  vibrate 
to  every  tone,  just  as  the  drum  of  the  ear  does ;  that  there  is  no 
analysis  of  complex  vibration  in  the  cochlea  or  elsewhere  in  the 
peripheral  mechanism  of  the  ear  ;  that  the  hair-cells  transform 
sound-vibrations  into  nerve-vibrations  similar  in  frequency  and 
amplitude  to  the  sound-vibrations  ;  that  simple  and  complex  vibra- 
tions of  nerve-molecules  arrive  in  the  sensory  cells  of  the  brain, 
and  there  produce,  not  sound  again,  of  course,  but  the  sensations 
of  sound,  the  nature  of  which  depends  not  upon  the  stimulation 
of  different  sensory  cells,  but  on  the  frequency,  the  amplitude, 
and  the  form  of  the  vibrations  coming  into  the  cells,  probably 
through  all  the  fibers  of  the  auditory  nerve."  This  explanation 
has  been  put  forth  by  Prof.  William  Rutherford  under  the  title  of 
the  "  Telephone  Theory  of  the  Sense  of  Hearing." 


620  THE  NERVOUS  SYSTEM. 

In  referring  to  this  subject,  Waller  compares  the  basilar  mem- 
brane to  the  rnembrana  tympani  in  the  following  language  :  "  It 
is  the  internal  drum-head,  repeating  the  complex  vibrations  of  the 
membrana  tympani,  and  vibrating  in  its  entire  area  to  all  sounds — 
although  more  in  some  parts  than  in  others— ^giving  what  we  may 
designate  as  acoustic  pressure  patterns  between  the  membrana 
tectoria  and  the  subjacent  field  of  hair-cells.  In  place  of  an 
analysis  by  sympathetic  vibration  of  particular  radial  fibers,  it 
may  be  imagined  that  varying  combinations  of  sound  give  vary- 
ing pressure  patterns,  comparable  to  the  varying  retinal  images  of 
external  objects." 

There  are  several  terms  used  in  the  discussion  of  the  subject 
of  sound  which  it  is  important  to  understand ;  especially  is  this 

true  for  the  medical  student,  for  he  will 
constantly  meet  them  in  his  study  of 
physical  diagnosis. 

Period;  Amplitude;  Frequency. — If  a 
weight  attached  to  a  rubber  cord  (Fig. 
398)  is  pulled  down  and  then  released, 
the  weight  and  the  particles  composing 
the  cord  will  vibrate,  and  any  particle, 
as  a,  will  oscillate  between  two  extreme 
points,  as  b  and  c,  which  are  equidistant 
from  a.  The  motion  of  a  from  c  to  b 
and  back  again  to  c  is  one  vibration  or 

one  complete  vibration,  and  the  time  this 
FIG.  398.— Weight  and  cord.  •        •      xi_  •    j      />    ,r          -u      x- 

occupies  is  the  period  ot  the  vibration. 
The  distance  from  a,  when  the  particle 

is  in  equilibrium,  to  b  or  to  c  is  the  amplitude  of  the  vibration, 
and  the  number  of  complete  vibrations  in  one  second  is  the  fre- 
quency. 

Noises. — These  are  sounds  produced  by  irregular  vibrations — 
i.  e.y  wanting  in  periodicity ;  or  by  discordant  or  dissonant  sounds 
— i.  e.,  sounds  which  differ  from  one  another  in  pitch ;  or  they 
may  be  single,  sudden  sounds,  as  the  report  of  a  cannon.  Noises 
are  disagreeable  sounds. 

Musical  Sounds. — These  are  sounds  produced  by  regular  vibra- 
tions, and  they  produce  a  pleasing  effect  upon  the  ear. 

It  should  be  said,  however,  that  what  may  under  some  circum- 
stances be  a  noise  may,  under  others,  produce  the  effect  of  a 
musical  tone.  Haughton  says  :  "  Nothing  can  be  imagined  more 
purely  a  noise  or  less  musical  than  the  jolt  of  the  rim  of  a  cab 
wheel  against  a  projecting  stone ;  yet  if  a  regularly  repeated 
succession  of  such  jolts  takes  place,  the  result  is  a  soft,  deep, 
musical  sound  that  will  bear  comparison  with  notes  derived  from 
more  sentimental  sources."  And  Zahm  says  :  "  With  a  sufficient 
number  of  properly  tuned  bottles  a  skilful  performer  could,  by 


SENSE  OF  HEARING.  621 

merely  withdrawing  the  corks,  easily  evoke  a  simple  melody  that 
every  one  would  recognize." 

Musical  sounds  differ  in  intensity,  pitch,  and  quality.  . 

Intensity. — This  depends  upon  the  energy  with  which  the 
particles  of  air  in  vibration  strike  upon  the  air,  and :  (1)  Varies 
directly  as  the  square  of  the  amplitude  of  vibration  of  the  sound- 
ing body ;  (2)  varies  inversely  as  the  square  of  its  distance ;  and 
(3)  diminishes  with  the  density  of  the  air. 

Loudness  is  oftentimes  spoken  of  as  synonymous  with  intensity, 
but  it  depends  somewhat  upon  the  condition  of  the  ear  and  upon 
the  rate  of  vibration,  all  sounds  not  affecting  the  ear  alike,  as  well 
as  upon  the  energy  of  vibration. 

Pitch. — This  depends  upon  the  frequency  of  vibration  or  vibra- 
tion frequency,  as  it  is  called ;  the  more  vibrations  per  second,  the 
higher  is  the  pitch.  There  must  be  at  least  30  vibrations  in  a 
second  to  produce  a  continuous  sound,  and  when  these  are  more 
frequent  than  38,000  in  a  second  they  become  inaudible,  at  least 
to  the  human  ear,  although  other  creatures  than  man  may  still 
hear  them.  These  limits  are  those  assigned  by  Helmholtz  ;  others 
give  the  lowest  number  as  16  and  the  highest  as  41,000.  Most 
musical  sounds  are  produced  by  vibrations  between  27  and  4000 
a  second. 

Quality. — This  is  called  also  timbre  and  tone-color.  As  it  is  a 
property  of  sound  which  is  difficult  to  understand,  and  even  to 
define,  we  will  quote  some  of  the  definitions  which  are  given  of  it. 
Thus  the  Standard  Dictionary  defines  " quality"  as  "That  which 
distinguishes  sounds  of  the  same  pitch  and  intensity  from  different 
sources,  as  from  different  instruments."  And  this  same  authority 
defines  " timbre"  as  "The  special  peculiarity  of  a  continuous 
sound  or  musical  tone,  or  that  common  to  all  tones  from  the  same 
source,  as  the  human  voice  or  some  particular  instrument,  dis- 
tinguishing them  from  notes  from  different  sources,  due  to  the 
special  form  of  the  sound-waves ;  the  quality  of  a  tone,  as  distin- 
guished from  intensity  and  pitch,  called  sometimes  tone-color." 
This  sentence  is  quoted  by  the  Standard  from  Silliman's  Physics  : 
"  The  essential  difference  between  the  bass  and  tenor  voices,  and 
between  the  contralto  and  soprano,  consists  in  the  tone  or  timbre 
which  distinguishes  them  even  when  they  are  singing  the  same 
note." 

Quality  is,  then,  concisely,  that  which  enables  us  to  distinguish 
one  sonorous  body  from  another — as,  a  piano  from  a  violin,  or  a 
flute  from  a  harp,  etc. ;  and  Helmholtz  has  demonstrated  that 
"the  quality  of  a  sound  is  determined  by  the  number,  order,  and 
relative  intensity  of  the  partial  tones  into  which  it  can  be  decom- 
posed" To  understand  this  it  will  be  necessary  to  consider 
briefly  the  compound  character  of  musical  sounds. 

Compound,  Fundamental,  and  Partial  Tones. — When  a  string 


622 


THE  NERVOUS  SYSTEM. 


stretched  between  two  points  is  set  in'  vibration,  as  by  drawing 
the  bow  of  a  violin  over  it,  it  will  vibrate  as  a  whole  (Fig.  399, 
a-b)  and  emit  a  tone  which,  being  the  lowest  that  it  can  emit,  is  its 
fundamental  or  prime  tone.  If  now  this  string  is  held  at  its 
middle  point,  c,  and  either  half  is  bowed,  that  half  of  the  string 
will  vibrate,  and  after  the  finger  has  been  removed  the  other  half 
will  also  vibrate,  and  the  tone  emitted  will  be  an  octave  higher ; 
in  a  similar  manner  the  string  may  be  held  at  one-third,  one- 
fourth,  etc.,  of  its  length,  and  the  string  when  bowed  will  divide 

into  three  or  four  segments,  and  the 
frequency  of  the  emitted  tones  will 
be  three  or  four  times  that  emitted 
by  the  string  when  it  vibrated  as  a 
whole.  Such  a  series  of  tones  is  a 
harmonic  series,  and  all  the  tones 
above  the  fundamental  are  har- 
monic overtones ,  or  upper  partial 
tones,  or  simply  partial  tones.  To 
demonstrate  this  more  effectively,  a 
sonometer  may  be  used,  which  con- 
sists of  a  wire  stretched  over  a  sounding-box  (Fig.  400)  with  a 
graduated  scale,  so  that  the  divisions  of  the  wire  may  be  accurately 
determined.  In  order  to  produce  these  overtones  it  is  not  neces- 
sary to  divide  the  string  with  the  finger,  or,  in  the  case  of  the  sonom- 
eter, the  wire  with  the  bridge ;  for  in  the  vibration  of  the  string 
or  wire  as  a  whole  it  divides  itself,  so  that  it  may  vibrate  as  a  whole 
and  also  in  segments ;  and  consequently,  while  the  whole  vibrat- 
ing string  or  wire  emits  the  fundamental  tone,  the  subdivided  seg- 
ments emit  each  its  own  partial  tone,  producing  therefore  compound 
tones,  the  fundamental  tone  determining  the  pitch.  As  a  rule,  the 


FIG.  399.— Vibrating  strings. 


FIG.  400.— Sonometer. 

sounds  of  musical  instruments  are  compound  tones,  and,  as  Helm- 
holtz  has  shown,  it  is  the  partial  tones  which  determine  their  quality 
by  which  they  are  differentiated  from  one  another,  there  being  no 
difference  in  the  fundamental  tones.  Thus  if  a  key  on  a  piano, 
say  "middle  C,"  is  struck,  the  string  will  vibrate^  as  a  whole 
1 32  times  in  a  second,  producing  one  fundamental  tone,  C,  and  it 
will  also  break  up  into  segments  which  will  vibrate  respectively 
264  times,  producing  the  octave  Cf ;  396  times,  producing  the  fifth 
above  this  ;  528  times,  producing  the  second  octave  C"  ;  660  times, 
producing  the  third  above  this,  etc. 


SENSE  OF  HEARING. 


623 


These  tones  are  believed  to  form  a  composite  wave,  and  as 
such  to  strike  the  membrana  tympani ;  and,  according  to  the 
"  piano  theory,"  this  wave  is  analyzed  into  its  component  tones 
by  the  basilar  membrane,  each  of  whose  fibers  is  caused  to  vibrate 
by  a  partial  tone ;  while  according  to  the  "  telephone  theory" 
this  analysis  takes  place  in  the  brain. 

Resonators. — That  musical  sounds  possess  this  compound  char- 
acter Helmholtz  demonstrated  by  means  of  resonators  (Fig.  401), 
which  consist  of  metallic  globes  of  various 
sizes  having  two  openings  of  unequal  diam- 
eter. If  one  of  these  is  held  with  its 
small  opening  to  the  ear,  and  the  large 
one  is  held  toward  a  source  of  sound,  the 
resonator  will  resound  when  a  tone  is 
emitted  which  corresponds  to  the  vibration- 
rate  of  its  contained  air,  and  to  no  other, 
and  by  using  a  series  of  these  the  various 
overtones  may  be  identified. 

To  sum  up  the  properties  of  sounds  and 

their  causes,  we  may  say  that  the  amplitude  of  a  wave  determines 
its  intensity  ;  its  vibration-frequency,  its  pitch  ;  its  form,  its  quality. 

Semicircular  Canals,  Utricle,  and  Saccule. — The  utricle  and 
saccule  have  been  regarded  by  some  authorities  as  having  the 
function  of  responding  to  irregular  vibrations,  and  as  being 
connected,  therefore,  with  the  perception  of  noises,  while  the 
perception  of  musical  sounds  depends  upon  the  cochlea ;  but 
the  consensus  of  opinion  now  is  that,  together  with  the  semicir- 
cular canals,  they  are  connected  with  the  important  function  of 
the  preservation  of  the  equilibrium  of  the  body,  the  utricle  and 
saccule  with  static  equilibrium — i.  e.,  when  the  body  is  in  a 
state  of  rest ;  the  semicircular  canals  with  dynamic  equilibrium — 
i.  e.,  when  the  body  is  in  motion.  This  subject  is  discussed  in 
connection  with  the  cerebellum  (p.  493). 


FIG.  401.— Resonator. 


V.  REPRODUCTIVE  FUNCTIONS. 


THE  reproductive  functions  are  those  concerned  in  the  perpetua- 
tion of  the  species.  In  the  lower  forms  of  animal  life,  where  the 
individual  consists  of  a- single  cell,  this  process  of  reproduction  is 
very  simple,  consisting  of  the  division  of  the  cell  into  two,  each 
of  which  has  the  power  of  dividing  to  form  new  individuals  in 
the  same  manner  as  it  was  formed.  This  is  asexual  reproduc- 
tion. In  the  higher  animals  the  reproduction  is  sexual — that  is, 
it  requires  the  union  of  two  elements  produced  in  the  organs  of 
two  individuals,  the  male  and  the  female,  neither  of  which  can 
accomplish  the  process  alone. 

REPRODUCTIVE  ORGANS. 

These  organs,  which  are  also  called  the  genital  or  generative 
organs,  are  in  the  male  the  testes,  each  with  its  duct,  the  vas 


FIG.  402.— Diagram  representing  the  male  genital  apparatus  of  right  side :  A, 
bladder ;  B,  prostatic  urethra ;  C,  membranous  urethra ;  I),  spongy  urethra.  1,  Eight 
testicle ;  2.  epididymis ;  3,  vas  deferens,  with  3',  its  ampulla ;  4,  seminal  vesicle ;  5, 
ejaculatory  duct  opening  at  the  verumontanum ;  6,  Cowper's  gland;  7,  its  excre- 
tory duct  (Testut). 

deferens,  the  vesiculae  seminales,  and  the  penis  (Fig.  402) ;  and  in 
the  female,  the  ovaries,  Fallopian  tubes,  uterus,  and  vagina. 

624 


GENITAL  ORGANS  OF  THE  MALE. 


625 


Genital  Organs  of  the  Male. — Testes. — The  testes  or 
testicles  (Fig.  403),  two  in  number,  are  situated  in  the  scrotum. 
They  are  composed  of  lobules,  the  number  of  which  in  each  testis 
is  variously  estimated  at  from  two  hundred  and  fifty  to  four 
hundred.  In  each  lobule  are  convoluted  seminiferous  tubules, 
tubuli  seminiferi,  varying  in  number  from  one  to  three. 

These  tubules  contain  epithelial  cells  of  two  varieties,  susten- 
tacular  cells,  or  Sartoli's  columns,  and  spermatogenic  cells,  the  latter 
being  related  only  to  the  formation  of  spermatozoa.  These  two 
varieties  of  cells  are  sometimes  described  as  the  parietal  cells. 
Internal  to  these  are  the  mother-cells,  which  are  derived  from  the 
spermatogenic  cells  by  the  process  of  mitosis  or  karyokinesis 


Globm  Major 


Vaga  Efferentia 


Globus  Minor 

FIG.  403.— Vertical  section  of  the  testicle  to  show  the  arrangement  of  the  ducts 

(Leroy). 

(p.  28).  These  give  rise  to  a  third  and  more  internal  layer  of 
daughter-cells,  from  whose  nuclei,  by  the  disappearance  of  the 
cell-body,  the  spermatoblasts  are  developed.  These  in  turn  become 
spermatozoa.  This  process  by  which  spermatozoa  are  formed  is 
known  as  spermatogenesis. 

Spermatozoa  (Fig.  404). — A  human  spermatozoon  is  about  50  /JL 
in  length,  and  consists  of  a  head  from  3  p  to  5  //  long,  a  body  and 
a  tail,  the  last  terminating  in  the  end-piece  of  Retzius,  which  is  the 
end  of  the  axial  fiber  which  runs  through  the  center  of  the  body 
and  tail.  The  tail  during  the  living  condition  is  in  rapid  motion, 
by  virtue  of  which  the  spermatozoon  can  travel  quite  rapidly.  The 
vitality  of  spermatozoa  is  considerable,  as  they  can  live  for  several 

40 


626 


REPRODUCTIVE  ORGANS. 


days  outside  the  body,  and  they  are  also  very  resistant  to  low 

temperatures.     They  appear  at  the 

a/"\  time   of  puberty,   and   have   been 

f      r «  found  in  individuals  ninety  years 

—     ^^   *  of  age,  though  they  are  not  com- 


FIG.  404. — Human  spermatozoa. 
The  two  at  the  left  after  Retzius; 
the  one  at  the  extreme  left  is  seen 
in  profile ;  the  others  in  surface  view ; 
the  one  at  the  right  is  drawn  as  de- 
scribed by  Jensen :  a,  head ;  b,  ter- 
minal nodule;  c,  middle  piece;  d, 
tail ;  e,  end-piece  of  Eetzius  (Bohm 
and  Davidoff). 


FIG.  405. — Spermatozoa :  a,  human  ;  6,  of 
the  rat;  c,  of  menobranchus  (X  480). 


Epithelium. 


Inner   longi- 
tudinal 
muscular 
layer. 


uter    longi- 
tudinal 
muscular 
layer. 


FIG.  406.— Cross-section  of  vas  deferens  near  the  epididymis  (human)  (Huber). 


GENITAL  ORGANS  OF  THE  MALE. 


627 


monly  found  in  semen  after  the  age  of  seventy  or  seventy-five 
years  is  past.  The  spermatozoa  of  different  animals  vary  in  size, 
though  their  general  appearance  is  much  the  same  (Fig.  405). 

Their  number  is  very  great ;  some  writers  state  that  in  a  single 
ejaculation  as  many  as  25,000,000  may  be  discharged,  while  one 
has  placed  their  number  as  high  as  412,500,000.  Both  figures  may 
be  correct,  inasmuch  as  the  amount  of  semen  ejaculated  varies  at 
each  emission. 

The  seminiferous  tubules  terminate  at  the  apices  of  the  lobules 


B 


FIG.  407.— Vas  deferens 
and  seminal  vesicle,  A,  seen 
in  longitudinal  and,  J?,  in 
horizontal  section :  1,  vas 
deferens ;  2,  its  terminal  or 
ampullary  portion ;  3,  semi- 
nal vesicle  with,  3',  its 
partitions;  4,  its  terminal 
portion ;  5,  ejaculatory  duct 
(Testut). 


FIG.  408.— Eight  seminal  vesicle,  unfolded  and 
seen  on  its  posterior  aspect  (subject  of  forty  years, 
previous  injection  of  tallow) :  1,  vas  deferens,  with, 
1',  its  ampulla ;  2,  seminal  vesicle  with,  3,  its  lateral 
prolongation  ;  4,  its  enlargements  in  form  of  cecum  ; 
5,  protuberances  of  its  wall ;  6,  junction  of  the 
vesicle  and  vas  deferens ;  7,  ejaculatory  duct 
(the  dotted  line,  x  x,  indicates  the  level  of  the 
upper  extremity  of  the  vesicle  before  its  unfolding) 
(Testut). 


in  the  vasa  recta  (straight  tubes),  about  thirty  in  number.  In  the 
mediastinum  these  tubes  form  a  network,  the  rete  testis,  the 
vessels  of  which  end  in  the  vasa  efferentia,  about  fifteen  in  number. 
These  vessels  connect  the  testicles  with  the  epididymis,  the  con- 
tinuation of  which  is  the  vas  deferens.  The  canals  of  the  rete 
testis  are  lined  by  non-ciliated  epithelium ;  the  vas  aberrans,  how- 


628 


REPRODUCTIVE  ORGANS. 


ever,  which  is  connected  with  it,  has  ciliated  epithelium.  Ciliated 
columnar  and  non-ciliated  cubical  epithelium  line  the  vasa 
efferentia. 

Vas  Deferens  (Fig.  406). — This  duct,  the  excretory  duct  of  the 


'frrs"-— 

FIG.  409. — Sagittal  section  through  the  ampulla  of  the  right  vas  deferens  and 
ejaculatory  duct :  1,  ampulla  of  vas  deferens ;  2,  ejaculatory  duct :  3,  seminal 
vesicle  dissected  away  in  its  middle  portion;  4,  its  opening  into  the  ejaculatory 
duct ;  5,  bladder  ;  6,  urethra ;  7,  prostate ;  8,  verumontanum. 

testis,  has  a  thick  muscular  wall.     Its  lining  epithelium  is  partly 
simple  ciliated  columnar,  and  partly  stratified  ciliated  columnar, 


FIG.  410.— Seminal  vesicles  and  vasa  deferentia,  posterior  view:  1,  bladder;  2, 
prostate;  3,  3',  seminal  vesicles;  4,  4',  vasa  deferentia;  5,  ejaculatory  ducts;  6,  6', 
ureters;  7,  7,  peri  vesicular  cul-de-sac  of  peritoneum;  8,  interdeferential  triangle,  in 
direct  relation  with  the  rectum,  from  which  it  is  separated  only  by  the  prostato- 
peritoneal  aponeurosis.  The  two  crosses  (+  -f )  indicate  the  points  at  which  the 
ureters  disappear  in  the  vesical  wall  (Testut). 

though  the  cilia  are  sometimes  absent.    At  the  base  of  the  bladder 
this  duct  lies  between  it  and  the  rectum,  and  here  presents  an 


GENITAL  ORGANS  OF  THE  MALE. 


629 


enlargement,  the  ampulla  (Figs.  407,  408),  beyond  which,  at  the 
base  of  the  prostate,  it  narrows  and  joins  with  the  duct  of  the 
vesicula  seminalis,  thus  forming  the  ejaculatory  duct  (Fig.  409). 
The  total  length  of  the  duct  is  about  60  cm. 

Vesicula  Seminalis  (Fig.  410). — This  structure  is  a  diverticulum 
from  the  vas  deferens,  and  glands  exist  in  its  mucous  membrane 
which  is  covered  with  non-ciliated  columnar  epithelium.  Some 
authorities  regard  it  as  a  storehouse  for  the  semen,  while  others  do 
not  regard  this  as  one  of  its  functions.  Bohm  and  Davidoff  state 
that  "  spermatozoa  are,  as  a  rule,  not  met  with  in  the  seminal 


FIG.  411. — Section  of  penis,  bladder,  etc. :  1,  symphysis  pubis ;  2,  prevesical 
space ;  3,  abdominal  wall ;  4,  bladder ;  5,  urachus ;  6,  seminal  vesicle  and  vas 
deferens ;  7,  prostate  ;  8,  plexus  of  Santorini ;  9,  sphincter  vesicae ;  10,  suspensory 
ligament  of  penis;  11,  penis  in  flaccid  condition;  12,  penis  in  state  of  erection  ;  13, 
glans  penis;  14,  bulb  of  urethra,;  15,  cul-de-sac  of  bulb.  '  a,  Prostatic  urethra;  6, 
membranous  urethra;  c,  spongy  urethra  (Testut). 

vesicles."  The  vas  deferens  and  especially  its  ampulla  serve  to 
retain  the  semen  until  ejaculated.  A  considerable  amount  of  fluid 
is  added  to  the  semen  by  the  secretion  of  the  mucous  membrane 
lining  the  vesicula  seminalis,  and  this  is  probably  its  most  im- 
portant function.  The  ejaculatory  ducts  discharge  into  the  urethra 
at  its  prostatic  part. 

The  prostate  gland  and  Cowper's  glands  contribute  also  to  the 
formation  of  the  semen. 

Semen. — The  semen  or  seminal  fluid  consists  of  secretions  from 


630 


REPRODUCTIVE  ORGANS. 


the  testes,  vasa  deferentia,  vesiculae  seminales,  prostate,  Cowper's 
glands,  and  the  muciparous  glands  of  the  urethra.  It  is  whitish 
in  color,  viscid  in  consistency,  alkaline  in  reaction,  and  possesses 
a  characteristic  odor.  The  amount  ejaculated  varies  from  0.5  c.c. 
to  6  c.c.  It  contains  from  82  to  90  per  cent,  of  water,  nuclein, 
protamin,  proteids,  xanthin,  lecithin,  cholesterin,  fat,  sodium  and 
potassium  chlorids,  sulphates,  and  phosphates.  From  it  may  be 
obtained  Charcot's  crystals,  which  are  a  phosphate  of  the  nitrogen- 
ous base,  spermin,  and  which  have 
their  origin  in  the  portion  of  the 
semen  which  is  contributed  by  the 
prostate;  to  the  decomposition  of 
the  substance  which  produces  these 
crystals  the  odor  of  the  semen  is  at- 
tributable. While  the  spermatozoa 
are  the  essential  fertilizing  agents, 
the  presence  of  the  fluid  portion  of 
the  semen  is  important  as  giving  to 
them  their  mobility,  without  which 
they  could  not  travel  in  the  genera- 
tive passages. 

Penis  (Fig.  411).— The  penis 
serves  a  double  purpose,  inasmuch 
as  it  is  the  organ  of  copulation  and 
also  the  termination  of  the  urinary 
passages.  The  former  function  is 
undoubtedly  the  essential  one,  for 

thefe  !s  DO  I^Bon  wh^  !he  urin"7 
passages  could  not  terminate  at  the 

surface  of  the  body  ;  it  is,  however, 
manifestly  advantageous  in  provid- 
ing for  the  perpetuation  of  the  spe- 
cies that  the  semen  should  be  ex- 
pelled as  near  as  possible  to  the 
mouth  of  the  uterus,  a  result  which 
is  obtained  by  the  intromission  of 
the  penis. 

The  penis  consists  of  erectile 
tissue  arranged  in  three  subdi- 
visions, two  above,  corpora  cavernosa,  and  one  below,  corpus 
spongiosum,  which  latter  terminates  in  the  glans  penis.  The 
corpora  cavernosa  are  surrounded  by  fibro-elastic  sheaths  from 
which  are  given  off  trabeculce.  These  pass  inward,  and  between 
them  are  spaces  which  contain  venous  blood.  A  similar  structure 
characterizes  the  corpus  spongiosum  which  encloses  the  urethra. 

The  arteries  which   supply  the  penis  are  derived  from   the 
internal  pudic  (Fig.  413).     Sensory  nerves  are  distributed  to  the 


FIG.  412. — Sagittal  section  of  the 
anterior  extremity  of  the  penis :  1, 
glans  penis ;  2,  corpus  cavernosum ; 
3,  3,  spongy  portion  of  urethra;  4, 
meatus  urinarius ;  5,  fossa  uavicularis ; 

6,  left  half  of  the  valve  of  Guerin ; 

7,  sinus  of  Guerin  between  the  valve 
and  the  anterior  wall  of  the  urethra ; 

8,  left  lateral  border  of  urethra;  9, 
its  lower  surface ;  10,  prepuce  pushed 
back  behind  the  glans ;  11,  frenum  ; 
12,  integument ;  13,  dorsal  vein ;  14, 
fibrous  partition  between  the  corpus 
cavernosum  and  corpus  spongiosum 
(Testut). 


GENITAL  ORGANS  OF  THE  FEMALE. 


631 


skin  of  the  penis,  and  especially  to  the  glans  penis,  where  they 
terminate  in  Meissner's  corpuscles,  Krause's  spheric  end-bulbs, 
and  genital  corpuscles  (Fig.  414). 


FIG.  413.— Diagram  of  the  arterial  circulation  of  the  penis :  1,  corpus  cavernosum, 
with  1',  its  root ;  2,  suspensory  ligament ;  3,  corpus  spongiosum  with  4,  bulb ;  5, 
glans;  6,  internal  pudic  artery;  7,  bulbo-urethral  artery,  with  7',  itsbulbar  branch, 
7",  its  anterior  branch  going  to  the  frenum;  8,  arteria  cavernosa,  with  8',  its  recur- 
rent branch ;  9,  dorsal  artery ;  10,  10,  its  lateral  branches ;  11,  its  termination  in 
the  glans  (Testut). 

Sensory  nerves  are  distributed  also  to  the  verumontanum,  in  the 
urethra,  and  the  pleasurable  sensations  connected  with  coitus  are 
due  to  the  excitation  of  the  nerves  here  distributed,  as  well  as 
to  those  supplying  the  glans 
penis. 

In  addition  to  sensory 
nerves  there  are  also  distrib- 
uted to  the  penis  e  x  c  i  t  o  r 
nerves,  nervi  erigentes,  which 
are  derived  from  the  first  and 
second,  and  sometimes  from 
the  third,  sacral  nerves ;  they 
are  vasodilator  nerves,  and 
have  their  origin  in  the  sex- 
ual center  of  the  spinal  cord. 

Genital  Organs  of  the 
Female. — Ovary. — The  ova- 
ries (Fig.  415),  two  in  num- 
ber, are  attached  to  the  pos- 
terior surface  of  the  broad 
ligament,  one  on  each  side  of 
the  uterus,  with  which  they 
are  connected  by  the  ova- 
rian ligament,  a  fibromuscular 
structure.  They  are  covered  by  peritoneum,  except  at  the  hilum, 
which  is,  however,  somewhat  modified,  its  mesothelial  cells  form- 
ing the  germinal  epithelium  (Fig.  416),  the  cells  of  which  are 


FIG.  414. — Genital  corpuscle  from  the 
glans  penis  of  man  ;  methylene-blue  stain 
(Dogiel,  Arch.  f.  mile.  Anat.,  vol.  xli.). 


632 


REPRODUCTIVE  ORGANS. 


FIG.  415. — Posterior  view  of  left  uterine  appendages:  1,  uterus  ;  2,  Fallopian  tubes; 
3,  fimbriated  extremity  and  opening  of  the  Fallopian  tube ;  4,  parovarium ;  5,  ovary  ; 
6,  broad  ligament;  7,  ovarian  ligament;  infundibulopelvic  ligament  (Henle). 


FIG.  416. — Section  through  part  of  ovary  of  adult  bitch :  a,  germinal  epithelium ; 
6,  6,  ingrowths  (egg-tubes)  from  the  germinal  epithelium,  seen  in  cross-section ;  c,  c, 
young  Graafian  follicles  in  the  cortical  layer ;  d,  a  more  mature  follicle,  containing 
two  ova  (this  is  rare) ;  e  and  /,  ova  surrounded  by  cells  of  discus  proligerus ;  g,  h, 
outer  and  inner  capsules  of  the  follicle;  i,  membrana  granulosa;  I,  blood-vessels; 
m,  m,  parovarium  ;  g,  germinal  epithelium  commencing  to  grow  in  and  form  an  egg- 
tube  ;  z,  transition  from  peritoneal  to  germinal  epithelium  (from  Waldeyer). 


GENITAL  OEGANS  OF  THE  FEMALE. 


633 


cubical  or  cylindrical  and  higher  than  those  of  the  rest  of  the 
peritoneum.  At  the  hilum  the  connective  tissue  of  the  ovarian 
ligament  passes  into  the  ovary,  forming  the  stroma  (Fig.  417), 
which  constitutes  the  greater  part  of  the  organ.  The  spindle- 
shaped  cells  of  the  stroma  are  regarded  by  His  as  unstriped 
muscle-cells,  while  Waldeyer,  Henle,  and  others  consider  them 
to  be  connective-tissue  cells.  Beneath  the  germinal  epithelium 
is  a  condensed  portion  of  the  stroma,  which  was  formerly  described 
under  the  name  of  tunica  albuginea,  and  was  regarded  as  a  cover- 
ing or  coat  of  the  ovary.  The  outer  third  of  the  ovary  is  the 
cortex,  while  the  inner  or  deeper  two-thirds  is  the  medulla,  in 


FIG.  417. — Part  of  the  same  section  as  represented  in  Fig.  415,  more  highly 
enlarged  :  1,  small  Graafian  follicles  near  the  surface ;  2,  fibrous  stroma  ;  3,  3',  less 
fibrous,  more  superficial  stroma  ;  4,  blood-vessels  ;  5,  a  follicle  still  further  advanced  ; 
6,  one  or  two  more  deeply  placed;  7,  one  further  developed,  enclosed  by  a  prolonga- 
tion of  the  fibrous  stroma ;  8,  part  of  the  largest  follicle ;  a,  membrana  granulosa ; 
b,  discus  proligerus;  c,  ovum;  d,  germinal  vesicle;  e,  germinal  spot  (Schron). 

which  are  the  blood-vessels  giving  to  this  medullary  portion 
another  name  by  which  it  is  sometimes  known,  zona  vasculosa. 
In  the  cortex  above  are  the  Graafian  follicles,  the  medulla  con- 
taining none  of  them.  These  are  sacs  varying  in  size  according 
to  the  stage  of  their  development.  In  the  Graafian  follicles 
are  the  ova,  the  least  developed  of  which  are  covered  by  a 
single  layer  of  cells,  those  further  advanced,  by  several  layers, 
constituting  the  membrana  grannlosa.  The  ova  and  the  cells  are 
derived  from  the  germinal  epithelium. 

A  mature  Graafian  follicle  (Fig.  418)  has  a  diameter  of  from 
8  to  19  mm.,  and  extends  from  the  medulla  to  the  surface  of  the 
ovary  and  projects  therefrom  (Fig.  419),  rupturing  at  the  most 


634 


REPRODUCTIVE  ORGANS. 


projecting  part  and  permitting  the  escape  of  the  ovum.     The  wall 
of  the  follicle,  theca  folliculi,  is  a  condensed  layer  of  the  stroma, 


Membrana 
granulosa. 


Discus 
proligerus. 

Ovtun. 

Germinal  vesicle. 


Blood-vessel. 

FIG.  418.— Section  of  fully  developed  Graafian  follicle  from  injected  ovary  of  pig; 
X  50  (Bohm  and  Davidoff ). 


and  is  itself  divisible  into  an  outer  layer  of  fibrous  connective 
tissue,  tunica  externa,  and  an  inner,  tunica  internet,  which  is  charac- 

_,     terized    by   the   presence   of 
^~x  -'l^i^L         blood-vessels    and    of    cells. 

Within  the  theca  is  the  mem- 
brana  granulosa  or  stratum 
granulosum,  which  is  com- 
posed of  several  layers  of 
small  polyhedral  cells.  In 
one  portion  of  the  membrana 
granulosa  the  cells  are  very 
numerous,  constituting  the 
discus  proligerus,  in  which 
the  ovum  lies  embedded. 
The  cells  of  the  discus  pro- 
ligerus which  are  in  contact  with  the  ovum  are  arranged  radially, 
constituting  the  corona  radiata  (Fig.  422).  Between  the  discus 
proligerus  and  the  membrana  granulosa,  except  at  the  point  where 
the  two  are  in  contact,  is  a  cavity,  the  antrum,  which  is  filled  with 


FIG.  419. — Ovary  with  mature  Graafian 
follicle  about  ready  to  burst  (Ribemont- 


GENITAL  ORGANS  OF  THE  FEMALE.  635 

a  Ruid,  liquor  folliculi,  formed  by  a  secretion  of  the  cells  and  by 
the  destruction  of  some  of  them. 

Graafian  follicles  continue  to  be  formed  in  the  ovary  for  a 
short  time  after  birth,  and  have  been  estimated  to  number,  in 
both  ovaries,  more  than  70,000 ;  but  a  small  proportion  of  these, 
however,  become  mature,  the  rest  undergoing  degeneration. 

During  the  development  of  Graafian  follicles  the  ova  which 
they  contain  also  become  developed  in  the  following  manner 
(Nagel,  Bohm  and  Davidoff).  In  the  early  period  of  the  develop- 
ment of  the  ovary  the  germinal  epithelium  pushes  into  the  sub- 
jacent connective  tissue  in  solid  projections  (Fig.  416);  these  form 
the  primary  egg-tubes  of  Pfluger,  some  of  the  cells  of  which  become 
ova,  while  others  become  Graafian  follicles.  The  differentiation 


FIG.  420. — Mature  ovuin  of  rabbit:  a,  cells  from  the  discus  proligerus  (epithe- 
lium of  cvum) ;  6,  zona  pellucida ;  c,  vitellus ;  d,  germinal  vesicle ;  e,  germinal 
spot ;  /,  large  globules  with  dull  luster  in  the  germinal  vesicle. 

of  the  cells  of  the  germinal  epithelium  into  ova  and  follicles  may 
occur  in  the  epithelium  itself,  in  which  case  the  larger  cells  con- 
stitute primitive  or  primordial  ova.  "  In  the  further  development 
of  the  ovarian  cortex  the  primitive  egg-tubes  are  penetrated 
throughout  by  connective  tissue,  so  that  each  egg-tube  is  separated 
into  a  number  of  irregular  divisions.  In  this  way  a  number  of 
distinct  epithelial  nests  are  formed,  which  lose  their  continuity 
with  the  germinal  epithelium  and  finally  lie  embedded  in  the  con- 
nective tissue.  According  to  the  shape  and  other  characteristics  of 
these  epithelial  nests,  we  may  distinguish  several  different  groups  : 
(1)  The  primitive  egg-tubes  of  Pfliiger ;  (2)  the  typical  primitive 
follicles — i.  e.,  those  which  contain  only  a  single  egg-cell  (present  in 
the  twenty-eighth  week  of  fetal  life) ;  (3)  the  atypical  follicles — i.  e., 


FIG.  424. 

FIGS.  421-424.— From  sections  of  cat's  ovary,  showing  ova  and  follicles  in 
different  stages  of  development:  a,  a,  a,  a,  germinal  spots;  6,  6,  6,  6  germinal 
vesicles  ;  c,  e,  c,  c,  ova  ;  d,  d,  d,  zonse  pellucidse  ;  e,  e,  e,  e,  corona  radiata  ;  /,  /,  /,  /, 
thecae  folliculorum  ;  g,  beginning  of  formation  of  the  cavity  of  the  follicle-  X*225 
(Bohm  and  Davidoff). 
636 


GENITAL   ORGANS  OF  THE  FEMALE.  637 

those  containing  two  or  three  egg-cells ;  (4)  the  so-called  nests  of 
follicles,  in  which  a  large  number  of  follicles  possess  only  a  single 
connective-tissue  envelope ;  (5)  follicles  of  the  last-named  type, 
which  may  assume  the  form  of  an  elongated  tube,  and  which  are 
then  known  as  the  constricted  tubes  of  Pfl  tiger.  The  fourth,  fifth, 
and  possibly  the  third  types  are  further  divided  by  connective- 
tissue  septa,  until  they  finally  form  distinct  and  typical  follicles 
(Schottlander). 

"  In  the  adult  ovary  true  egg-tubes  are  no  longer  developed. 
Isolated  invaginations  of  the  germinal  epithelium  sometimes 
occur,  but  apparently  lead  merely  to  the  formation  of  epithelial 
cysts  (Schottlander).  The  theories  as  to  when  the  formation  of 
new  epithelial  nests  or  follicles  ceases  are,  however,  very  conflict- 
ing, some  authors  believing  that  cessation  takes  place  at  birth, 
others  that  it  continues  into  childhood  and  even  into  middle 
age. 

"  The  ova  of  the  primitive  or  primordial  follicles  attain  a  size 
(in  fresh  tissue  teased  in  normal  salt  solution)  varying  from  48  fj. 
to  69  //.  They  possess  a  nucleus  varying  in  size  from  20  -/JL  to  32  p., 
presenting  a  doubly  contoured  nuclear  membrane,  and  containing 
a  distinct  chromatin  network  with  a  nucleolus  and  several  accessory 
nucleoli.  The  protoplasm  shows  a  distinct  spongioplastic  network 
containing  a  clear  hyaloplasm.  The  primitive  ova,  until  they 
undergo  development,  retain  this  size  and  structure,  irrespective 
of  the  age  of  the  individual.  They  are  numerous  in  embryonic 
life  and  early  childhood,  always  found  during  the  ovulation  period, 
but  not  observed  in  the  ovaries  of  the  aged.  Changes  in  the  size 
and  structure  of  the  ova  accompany  the  proliferation  of  the 
foilicular  cells  in  the  growing  follicles.  As  soon  as  the  follicular 
cells  of  a  primitive  follicle  proliferate,  as  above  described,  the 
ovum  of  the  follicle  increases  in  size  until  it  has  attained  the  size 
of  a  fully  developed  ovum.  The  zona  pellucida  now  makes  its 
appearance,  and  after  this  has  reached  a  certain  thickness,  yolk 
granules  (deutoplastic  granules)  develop  in  the  protoplasm  of  the 
ovum.  In  a  fully  developed  Graafian  follicle  the  ovum  presents 
an  outer  clearer  protoplasmic  zone  and  an  inner  fine  granular  zone 
containing  yolk-granules ;  in  the  former  lies  the  germinal  vesicle. 
Between  the  protoplasm  of  the  ovum  and  the  zona  pellucida  is 
found  a  narrow  space  known  as  the  perivitelline  space.  The 
germinal  vesicle  (nucleus),  which  is  usually  of  spherical  shape, 
possesses  a  doubly  contoured  membrane  and  a  large  germinal  spot 
(nucleolus),  which  shows  ameboid  movements. 

"  The  origin  of  the  zona  pellucida  has  not  as  yet  been  fully 
determined.  It  probably  represents  a  product  of  the  egg-epithe- 
lium, and  may  be  regarded  in  general  as  a  cuticular  formation  of 
these  cells.  At  all  events  it  contains  numerous  small  canals  or 
pores  into  which  the  processes  of  the  cells  composing  the  corona 


638  REPRODUCTIVE  ORGANS. 

radiata  extend.  These  processes  are  to  be  regarded  as  inter- 
cellular bridges  (Retzius) ;  and,  according  to  Palladino,  they  occur 
not  only  between  the  ovum  and  the  corona  radiata,  but  also 
between  the  follicular  cells  themselves.  In  the  ripe  human  ovum 
the  pores  are  apparently  absent  (Nagel),  and  it  is  very  probable 
that  they  have  to  do  with  the  passage  of  nourishment  to  the  grow- 
ing egg.  Retzius  believes  that  the  zona  pellucida  is  derived  from 
the  processes  of  the  cells  composing  the  corona  radiata,  which  at 
first  interlace  and  form  a  network  around  the  ovum.  Later,  the 
matrix  of  the  membrane  is  deposited  in  the  meshes  of  the  net- 
work, very  probably  by  the  egg  itself." 

Ovum. — The  human  ovum  has  a  diameter  of  from  0.22  to  0.32 
mm.  The  external  envelope  is  the  zona  pellucida,  the  origin  of 
which,  as  has  been  stated,  is  uncertain.  Within  this  is  the  vitellus 
with  its  nucleus,  the  germinal  vesicle,  whose  diameter  is  from  30  p 
to  40  //.  The  vitellus  consists  of  a  protoplasmic  network,  in  the 


FIG.  425. — Portion  of  broad  ligament  stretched  to  show  the  parovarium  (p)  lying 
between  the  folds  and  consisting  of  the  head-tube  and  cross-tubules  (Gegenbaur). 

meshes  of  which  are  embedded  highly  refractive  oval  bodies,  the 
yolk-globules. 

The  germinal  vesicle  has  a  distinct  enveloping  membrane,  and 
within  it  is  a  scanty  framework  with  a  small  amount  of  chromatin, 
and  one  or  two  false  nucleoli,  germinal  spots,  due  to  the  thickening 
of  the  chromatin.  These  structures  have  a  diameter  of  from  7  JJL 
to  10  p. 

Parovarium  (Fig.  425). — This  structure  is  known  also  as  the 
epoophoron  and  the  organ  of  Rosenmutter.  It  lies  within  the 
b^oad  ligament,  between  the  Fallopian  tube  and  the  ovary,  and 
represents  what  remains  of  the  Wolffian  body  of  the  fetus.  The 
tubules  of  that  organ  being  the  short  canals  of  the  parovarium, 
and  the  upper  part  of  the  Wolffian  duct  being  represented  by  the 
head-tube.  This  latter  sometimes  persists  as  a  patent  canal,  con- 
stituting Gartner**  duct,  which  is  the  homologue  of  the  vas 
deferens.  The  paroophoron  is  a  structure  sometimes  observed 


GENITAL  ORGANS  OF  THE  FEMALE. 


639 


within  the  broad  ligament  near  the  ovary,  ordinarily  closer  to  the 
uterus  than  the  parovarium.     It  appears  also  as  tubules,  and  these 


FIG.  426. — Dissection  of  the  pelvic  organs,  showing  the  relation  of  the  abdominal 
parietes  to  the  round  ligaments  and  the  bladder :  1,  3,  the  obliterated  hypogastric 
arteries;  the  urachus  (Bourgery  arid  Jacob). 

correspond  to  the  transverse  tubules  of  the  lowest  part  of  the 
fetal    Wolffian   bodv.     The  tubules   in  adult  life  sometimes  be- 


FIG.  427.— Fallopian  tube  laid  open  :  a,  6,  uterine  portion  of  tube  ;  c,  d,  folds  of 
mucous  membrane ;  e,  tubo-ovarian  ligament  or  fimbria  ovarica ;  /,  ovary ;  g,  round 
ligament  (from  Playfair). 

come  distended,  forming  cysts  which  require  operative  interference 
for  their  removal. 


640 


REPRODUCTIVE  ORGANS. 


Fallopian  Tubes  (Figs.  427,  428). — Tnese  tubes  are  each  about 
10  cm.  in  length,  and  extend  from  the  angles  of  the  uterus  to 
the  vicinity  of  the  ovaries.  The  ovarian  extremity  of  each 
tube  expands  into  a  funnel-shaped  opening,  the  pavilion  or  infundi- 
bulum,  which  is  surrounded  by  fringed  processes,  the  fimbrise. 
At  the  uterine  extremity  its  lumen  will  scarcely  admit  a  bristle, 
while  at  the  ostium  abdominale,  the  outer  opening  where  the  tube 
expands  into  the  infundibulum,  its  diameter  is  about  4  mm. 

The  tube  is  composed  of  three  coats,  an  internal  mucous,  next 
to  this  a  muscular,  and,  most  external,  a  serous  or  peritoneal.  The 


FiG.  428,— Transverse  section  of  Fallopian  tube,  showing  the  complicated  arrange- 
ment of  the  longitudinal  plications  which  are  here  cut  across  (Martin). 

mucous  membrane  is  arranged  in  longitudinal  folds  (Figs.  427, 
428)  and  covered  by  a  single  layer  of  ciliated  columnar  epithe- 
lium. There  are  no  distinct  glands  in  the  duct,  though  some 
writers  regard  the  crypts  as  fulfilling  the  function  of  glands.  The 
muscular  coat  consists  of  an  inner  circular  and  an  outer  longitu- 
dinal layer. 

Uterus  (Fig.  429). — This  organ  in  the  virgin  condition  has  a 
length  of  about  7.5  cm.,  a  width  of  4  cm.  at  its  widest  part,  and 
a  thickness  of  2.5  cm.  It  is  divided  into  a  body  or  corpus  and  a 
neck  or  cervix,  and  is  composed  of  three  coats — mucous,  muscular, 
and  peritoneal.  The  mucous,  which  is  the  internal  coat,  is  covered 


GENITAL   ORGANS  OF  THE  FEMALE. 


641 


by  a  single  layer  of  columnar  ciliated  epithelium,  that  extends 
to  the   external   os,   where   the   epithelium   is   of  the   stratified 


Tube. 


Reflection  of. 
peritoneum. 


FIG.  429. — Anterior  view  of  virgin  uterus,  showing  relations  of  cervix  to  corpus 
uteri  and  reflection  of  peritoneum  at  isthmus. 

squamous  variety.     Some  authorities  describe  this  latter  variety 
of  epithelium  as  covering  the  lower  third  of  the  cervical  mucous 


FIG.  430. — Section  of  human  uterus,  including  mucosa  (a)  and  adjacent  mus- 
cular tissue  (6) ;  c,  epithelium  of  free  surface  and  tubular  uterine  glands  (d) ;  /, 
deepest  layer  of  mucosa,  containing  fundi  of  glands;  h,  strands  of  non-striped 
muscle  penetrating  within  the  mucosa  (Piersol). 

membrane.    In  the  mucous  membrane  are  numerous  uterine  glands 
(Fig.   430),   into   which   the   ciliated   epithelium  extends.     The 
41 


642 


REPRODUCTIVE  ORGANS. 


motion  of  the  cilia  of  the  uterine  mucous  membrane  is  toward 
the  vagina.  In  the  mucous  membrane  of  the  cervix  are  closed 
sacs  lined  by  cylindrical  or  ciliated  epithelium ;  these  are  the 
ovula  Nabothi,  and  are  regarded  as  cystic  formations. 

The  muscular  coat  (Fig.  431)  consists  of  three  layers :  An 
inner  and  an  outer,  both  longitudinal ;  and  a  middle  circular,  which 
is  more  highly  developed  than  the  other  two.  The  muscular 
tissue  is  of  the  unstriped  variety  (Fig.  432). 

Ovtllation. — The  formation  of  ova  in  the  human  female  is 


FIG.  431.—  Arrangement  of  uterine  muscle,  as  seen  from  in  front  after  removal  of 

serous  coat  (Helie). 

probably  complete  two  years  after  birth.  Although  during  this 
period,  and,  indeed,  even  before  birth,  some  ova  may  undergo 
development  to  some  extent,  still  it  is  not  until  the  period  of 
puberty  that  there  is  any  approach  to  regularity  in  the  develop- 
ment of  either  the  Graafian  follicles  or  the  ova.  At  undetermined 
periods  Graafian  follicles  rupture  and  mature  ova  are  discharged, 
together  with  the  cells  of  the  discus  proligerus.  This  ripening 
and  discharge  of  ova  constitute  ovula tion.  The  cause  of  the 


OVULATION. 


643 


rupture  of  the  follicle  is  still  an  unsettled  question.    In  discussing 
this  subject  Bohm  and  Davidoff  say  : 

"The  manner  in  which  the  fully  developed  Graafian  follicle 
bursts  and  its  ovum  is  freed  is  still  a  subject  of  controversy ;  the 
following  may  be  said  regarding  it :  By  a  softening  of  the  cells 
forming  the  pedicle  of  the  discus  proligerus,  the  latter,  together 
with  the  ovum,  are  separated  from  the  remaining  granulosa,  and 
lie  free  in  the  liquor  folliculi.  At  the  point  where  the  follicle 
comes  in  contact  with  the  tunica  albuginea  of  the  ovary  the  latter, 
with  the  theca  folliculi,  becomes  thin,  and  in  this  region,  known 
as  the  stigma,  the  blood-vessels  are  obliterated  and  the  entire 
tissue  gradually  atrophies;  thus  a  point  of  least  resistance  is 


FIG.  432.— A,  isolated  muscle-elements  of  the  non-pregnant  uterus ;  B,  cells  from 
the  organ  shortly  after  delivery  (Sappey). 

formed  which  gives  way  at  the  slightest  increase  in  pressure  within 
the  follicle,  or  in  its  neighborhood. 

"The  increase  of  pressure  within  the  follicle,  leading  to  its 
rupture,  is,  according  to  Nagel,  due  to  a  thickening  of  the  tunica 
mterna  of  the  theca  of  the  follicle.  The  cells  of  this  layer  pro- 
liferate and  increase  in  size  and  show  yellowish  colored  granules. 
This  cell-proliferation  leads  to  a  folding  of  the  tunica  interna,  the 
folds  encroaching  on  the  cavity  of  the  follicle,  and  causing  its 
contents  to  be  pushed  toward  the  stigma." 

Piersol  states  that  the  liberation  of  the  ova  usually  takes 
place  at  definite  times,  which  in  general  coincide  with  the  men- 
strual epochs,  one  or  more  ova  being  set  free  at  each  period.  This 


644  REPRODUCTIVE  ORGANS. 

t 

coincidence,  however,  is  by  no  means  necessary  or  invariable,  since 
ovulation  undoubtedly  proceeds  independently  of  menstruation. 
Other  authorities  regard  the  intervals  between  periods  of  ovula- 
tion as  very  irregular.  J.  Bland  Button,  in  his  Surgical  Diseases 
of  the  Ovaries  and  Fallopian  Tubes,  says  :  "  In  the  ovary  of  the 
human  fetus  ova  ripen,  form  follicles,  and  undergo  suppression 
during  the  last  month  of  Ultra-uterine  life.  The  life  of  the  human 
ovary  may  be  divided  into  the  following  periods  of  activity  and 
repose :  The  first  period  extends  from  the  seventh  month  of  intra- 
uterine  life  to  the  end  of  the  first  year.  Ova  ripen  in  such  abund- 
ance that  in  some  cases  a  marked  diminution  in  the  number  of  the 
ova  is  appreciable  at  the  second  year  after  birth.  To  this  succeeds 
a  period  of  comparative  repose,  terminating  at  the  tenth  or  twelfth 
year ;  then  the  ripening  of  the  ova  is  again  easily  detected,  and 
goes  on  independently  of  menstruation,  even  after  the  accession  of 
the  climacteric." 

In  an  uncertain  proportion  of  instances  the  ova  find  their  way 
into  the  Fallopian  tube.  The  mechanism  by  which  this  is  accom- 
plished is  still  a  matter  of  doubt.  One  theory  maintains  that  the 
fimbriated  extremity  is  so  approximated  to  the  ovary  as  to  bring 
the  ostium  abdominale  against  the  part  at  which  the  Graafian 
vesicle  is  about  to  rupture,  and  that  the  escaping  ovum  thus  enters 
the  tube.  This  approximation  is  by  some  writers  supposed  to  be 
due  to  an  engorgement  of  the  fimbriated  extremity  by  blood,  thus 
causing  its  erection  and  approximation,  but  the  absence  of  erectile 
tissue  disproves  this  theory.  Tait  found,  in  certain  cases  upon 
which  he  operated,  the  tube  grasping  the  ovary,  and  he  attributed 
this  action  to  muscular  fibers  in  the  tube  which  develop  at  the 
period  of  puberty  and  which  atrophy  at  the  menopause,  so  that 
ova  can  enter  the  tube  only  during  the  active  life  of  these  fibers, 
and  then,  and  then  only,  can  pregnancy  take  place,  though  both 
before  puberty  and  after  the  menopause  ovulation  may  occur,  fhe 
ova  under  these  circumstances  falling  into  the  abdominal  cavity, 
where  they  disintegrate.  According  to  this  theory,  if  ovulation  takes 
place  and  the  tube  does  not  grasp  the  ovary,  the  ovum  when  dis- 
charged does  not  enter  the  tube,  but  falls  into  the  abdominal  cavity. 

The  second  theory  is  that  this  grasping  of  the  ovary  by  the 
tube  does  not  occur,  but  that  the  ovum  is  carried  into  the  ostium 
abdominale  by  the  current  created  by  the  ciliated  epithelium  lining 
the  fimbrise. 

This  latter  theory  is  the  one  generally  accepted  at  the  present 
time.  Indeed,  facts  are  accumulating  to  show  that  this  current  is 
sufficiently  powerful  to  carry  an  ovum  from  one  ovary  to  the  tube 
of  the  opposite  side.  Kelly  removed  a  diseased  left  ovary  and 
right  tube  from  a  woman  who,  fifteen  months  later,  was  delivered 
of  a  child  at  term.  In  this  instance  the  ovum  must  have  come 
from  the  right  ovary  and  been  carried  to  the  uterus  through  the 


MENSTRUATION.  645 

left  tube.  This  passage  of  an  ovum  from  one  ovary  to  the  tube 
of  the  opposite  side  is  external  migration,  and  is  perhaps  not  as 
infrequent  as  would  at  first  be  thought.  Internal  migration  is  the 
passing  of  an  ovum  from  an  ovary  down  the  tube  of  the  same  side, 
through  the  uterine  cavity,  and  to  a  greater  or  less  extent  up  the 
tube  of  the  opposite  side.  Internal  migration  is  supposed  to  account 
for  some  tubal  pregnancies.  It  is  doubtful  if  it  ever  occurs.  It  is 
to  be  remembered  that  the  ovum  is  but  0.25  mm.  in  diameter,  and 
there  seems  no  reason  to  question  the  power  of  the  current  to  draw 
so  small  a  body  into  the  tube.  Once  in  the  tube,  it  is  carried  on 
to  the  uterus  by  the  ciliated  epithelium. 

Menstruation. — At  about  the  age  of  fourteen  years  a  bloody 
discharge  takes  place  from  the  vagina  at  intervals  of  about  four 
weeks.  This  is  the  menses,  and  the  process  is  menstruation.  It 
should  be  noted  that  the  period  of  life  at  which  menstruation 
appears  is  by  no  means  uniform  in  all  individuals. 

Byron  Robinson,  in  the  Medical  Brief,  says  that  "  the  influ- 
ences which  change  the  individual  age  of  beginning  are  :  Climate, 
race,  residence,  altitude,  latitude  and  longitude,  environments, 
food,  and  disease.  Climate  (atmospheric  and  geographical  rela- 
tions) exercises  the  chief  influence  among  the  various  factors. 
In  general,  the  hotter  the  climate  the  earlier  the  menstruation 
begins.  The  average  age  for  the  beginning  of  menstruation  is : 
Chicago,  fourteen ;  Sweden,  eighteen ;  Norway,  sixteen  and  one- 
half;  Denmark,  sixteen  and  three-fourths;  Russia,  fourteen; 
Germany,  fifteen  ;  Great  Britain,  fifteen  ;  Austria,  sixteen  ;  Pales- 
tine, thirteen  ;  Turkey,  eleven  ;  Syria,  twelve  ;  Ceylon,  Siam,  and 
Japan,  thirteen." 

Prof.  Skene,  in  his  Diseases  of  Women,  lays  down  the  follow- 
ing rules  : 

1.  Menstruation  should  begin  at  puberty — that  is,  when  the 
woman  is  maturely  developed,  no  matter  what  the  age  may  be. 

2.  It  should  recur  at  regular  intervals :  about  every  twenty- 
eight  days  is  the  average  time.     A  regular  periodicity  is  normal, 
but  the  duration  of  the  periods  often  differs  in  different  persons. 

3.  The  discharge  should  always  be  fluid  in  consistence  and 
sanguineous  in  color. 

4.  The  flow   should   continue  a  definite  length  of  time,   the 
duration  depending  upon  the  habit  of  each  case ;  at  least  there 
should  not  be  any  great  deviation  from  this  rule.     The  duration 
is  usually  from  three  to  five  days,  and  the  total  amount  is  about 
four  or  five  ounces. 

At  about  the  age  of  forty-five  years  menstruation  ceases  :  this 
is  the  menopause,  or  climacteric,  or  change  of  life.  The  cessation 
is  not  abrupt,  but  gradual.  The  menstruation  becomes  irregular, 
and  finally  ceases  altogether. 

The  changes  which  take  place  in  the  mucous  membrane  of 


646  REPRODUCTIVE  ORGANS. 

the  body  of  the  uterus  during  menstruation  are  not  agreed  upon 
by  authorities. 

Webster  says  that  "the  latest  evidence  points  clearly  to  the 
view  that  there  is  but  a  slight  denudation,  irregular  in  distribution 
in  the  superficial  layers  of  the  mucosa." 

The  complete  menstrual  cycle  is,  according  to  Marshall,  as 
quoted  by  the  American  Text-book  of  Obstetrics,  divisible  into 
four  stages  :  (1)  The  first  or  constructive  stage  is  one  of  prepara- 
tion for  the  reception  of  an  ovum,  and  is  characterized  by  the 
formation  of  a  menstrual  decidua,  in  the  preparation  of  which 
swelling  of  the  mucous  membrane,  enlargement  of  the  uterine 
glands,  and  increase  of  the  connective  tissue,  all  take  place.  This 
stage  probably  lasts  one  week,  and  is  followed,  when  pregnancy 
has  not  occurred,  by  degenerative  changes. 

(2)  The  second  or  destructive  stage  is  marked  by  the  destruc- 
tive processes  which  give  rise  to  the  usual  phenomena  of  the 


FIG.  433. — Uterus  during  menstruation,  cut  open  to  show  the  swelling  of  the 
whole  organ,  and  particularly  the  mucous  membrane :  A,  mucous  membrane  of 
cervix;  B,  C,  mucous  membrane  of  corpus,  much  thickened;  D,  muscular  layer; 
E,  uterine  opening  of  tube;  F,  os  internum  (the  mucous  membrane  tapers  down 
to  these  openings)  (Courty). 

menstrual  period,  including  the  discharge  of  mucus,  blood,  and 
disintegrated  uterine  mucous  membrane.  Five  days  constitute  the 
average  duration  of  the  menstrual  flow,  although  its  continuance 
may  be  extended  or  curtailed,  owing  to  individual  peculiarities. 


MENSTR  UA  TION.  647 

(3)  The  third  or  reparative  stage  is  one  of  repair,  during  which 
the  deeper  and  unaffected  parts  of  the  uterine  mucous  membrane 
institute  constructive  processes,  which  within  the  short  period  of 
from  three  to  four  days  result  in  the  formation  of  a  new  mucosa. 

(4)  The  fourth  or  quiescent  stage  includes  the  remaining  twelve 
or  fourteen  days  of  the  menstrual  cycle,  and  represents  the  qui- 
escent period  preceding  the  initiative  changes  marking  the  begin- 
ning of  the  next  period. 

Cause  of  Menstruation. — The  cause  of  menstruation  is  still 
undetermined. 

Lawson  Tait  held  that  menstruation  was  dependent  upon  the 
oviducts,  but  that  ovulation  and  menstruation  were  independent 
functions. 

Johnstone  believed  that  menstruation  is  regulated  by  a  nerve 
which  passes  through  the  broad  ligament. 

Byron  Kobinson  holds  that  menstruation  is  due  to  ganglia 
located  in  the  walls  of  the  uterus  and  oviducts,  which  he  terms 
"  automatic  menstrual  ganglia."  He  considers  it  to  be  independent 
of  ovulation.  He  calls  the  ovary  the  chief  central  sexual  organ 
of  woman,  and  the  uterus  and  oviducts  appendages  of  the  ovary. 

According  to  this  writer  (loo.  cit.)  menstruation  is  due  to  a 
nervous  mechanism  termed  automatic  menstrual  ganglia,  located 
in  the  walls  of  the  uterus  and  oviducts.  Its  utility  is  the  secre- 
tion of  fluid  to  float  an  egg  into  the  uterus.  Its  design  is  repro- 
duction. 

"Among  the  lower  animals  menstruation  and  ovulation  are 
concomitant,  but  as  the  scale  of  life  ascends  they  become  separate 
processes.  Man  and  monkey  are  probably  the  only  animals  with 
a  distinct  rhythmical  or  periodical  menstrual  discharge  independent 
of  ovulation.  This  process  in  lower  animals  is  called  cestrus  or 
'  rut.'  Menstruation  is  limited  to  a  certain  period  of  life,  seed- 
time and  harvest,  generally  from  the  fifteenth  to  the  forty-fifth 
year.  It  is  due  to  automatic  menstrual  ganglia,  small  nerve- 
ganglia  situated  in  the  walls  of  the  uterus  and  tubes.  It  is  a 
manifestation  of  the  nervous  system.  It  must  be  remembered 
that  a  nerve-ganglion  is  a  small  brain ;  it  receives  sensation  and 
sends  out  motion  ;  it  assimilates  food,  and  is  a  trophic  center ; 
it  reproduces  itself,  and  controls  secretion  and  vermicular  action ; 
it  is  a  physiological  center,  and  has  all  the  elements  of  a  brain. 
These  little  ganglia  are  situated  along  the  uterus  and  oviducts 
passing  through  a  monthly  rhythm,  rising  and  sinking  between 
the  extremes  of  functional  activity  and  repose,  and  corresponding 
in  these  states  to  the  menstrual  congestion  and  intermenstrual 
quietude  of  the  uterus  and  oviducts.  The  oviducts  at  the  monthly 
periods  assume  peristaltic  motion,  a  vermicular  or  tortuous  action, 
so  that  an  ovum  may  be  carried  to  the  uterus  by  their  movements. 
It  may  be  observed  that  when  the  ganglia  along  the  oviducts  are 


648  REPRODUCTIVE  ORGANS. 

in  the  slightest  action,  the  oviducts  become  filled  with  fluid  secreted 
from  the  blood,  which  is  whipped  in  a  stream  toward  the  uterus 
by  the  cilia  that  always  move  in  that  direction.  This  oviductal 
fluid  furnishes  a  canal  in  which  the  ovum  can  float  to  the  uterus ; 
for  in  a  dry,  contracted  oviduct  an  egg  could  pass  only  with 
difficulty.  The  automatic  menstrual  ganglia  are  similar  to  the 
other  visceral  ganglia,  such  as  the  cardiac  and  those  of  the 
digestive  tract,  and  the  renal  ganglia." 

Christopher  Martin  states  his  views  on  the  subject  as  follows  : 

Menstruation  is  a  process  directly  controlled  by  a  special 
nerve-center  situated  in  the  lumbar  part  of  the  spinal  cord,  and 
the  changes  in  the  uterine  mucosa  during  the  period  are  brought 
about  by  katabolic  nerves,  and  during  the  interval  by  anabolic 
nerves.  The  menstrual  impulses  reach  the  uterus  either  through 
the  pelvic  splanchnic  or  the  ovarian  plexus,  possibly  through  both. 
And,  finally,  removal  of  the  uterine  appendages  arrests  menstrua- 
tion by  severing  the  menstrual  nerves. 

Relation  between  Ovulation  and  Menstruation. — The  relation 
between  these  two  processes  is  as  yet  undetermined,  although 
physiologists  in  the  main  hold  that  at  the  time  of  the  discharge  of 
an  ovum  from  an  ovary  there  is  such  a  condition  of  the  uterus  as 
brings  about  its  increased  vascularity  and  the  oozing  from  its  ves- 
sels of  the  menstrual  blood.  They  believe  that  at  each  menstru- 
ation there  is  discharge  of  an  ovum.  Other  writers — and  these 
are  principally  surgeons  who  have  devoted  much  time  to  the  study 
of  diseases  of  women,  and  who  have  had  large  experience  in  opera- 
tions for  the  removal  of  the  ovaries — differ  very  materially  from 
the  physiologists.  One  of  the  number  (A.  Reeves  Jackson,  in  an 
article  entitled  "  Ovular  Theory  of  Menstruation  :  Will  it  Stand  ?  " 
in  the  American  Journal  of  Obstetrics)  says :  "  Menstruation  may 
occur  without  accompanying  ovulation ;  ovulation  may  occur 
without  accompanying  menstruation  ;  and  ovulation  is  the  irreg- 
ular but  constant  function  of  the  ovaries,  while  menstruation  is 
the  regular  rhythmical  function  of  the  uterus."  Lawson  Tait, 
the  celebrated  surgeon,  says  that  "  ovulation  and  menstruation  are 
not  only  not  concurrent,  but  ovulation  is  much  less  frequent  than 
menstruation."  J.  Bland  Button,  already  referred  to,  says  :  "  It 
is  very  difficult  to  uproot  ancient  tradition,  especially  one  so  ancient 
as  the  belief  in  the  intimate  association  of  ovulation  and  men- 
struation, but  evidence  is  rapidly  accumulating  which  will  show 
that  the  two  processes  are  not  so  intimately  connected  as  was 
formerly  supposed. " 

Leopold  and  Mironoff  state,  as  their  opinion,  that  "  Ovulation 
usually  accompanies  menstruation,  though  not  always.  Menstru- 
ation depends  upon  the  presence  of  the  ovaries  and  a  well-formed 
uterine  mucosa.  Ovulation  usually  coincides  with  menstruation  ;  it 
rarely  occurs  in  normal  conditions  between  the  menstrual  periods." 


MENSTR  UA  TION.  649 

Manton,  in  Jewett's  Practice  of  Obstetrics,  says  :  "  Although 
menstruation  and  ovulation  should  not  be  considered  as  necessarily 
coincident  processes,  it  is  altogether  probable  that  the  conditions 
which  influence  the  one  have  also  an  effect  upon  the  other,  and  that, 
as  a  rule,  the  two  functions  occur  simultaneously  and  are,  to  a 
greater  or  less  extent,  interdependent." 

Williams  concludes,  from  all  the  available  evidence,  "  that  the 
two  processes  usually  occur  about  the  same  time,  but  that  one  not 
infrequently  antedates  the  other  by  a  few  days  ;  while  in  exceptional 
cases  they  may  occur  quite  independently." 

In  discussing  the  relation  between  menstruation  and  ovulation, 
Edgar  says  that  "  they  occur  about  the  same  time,  although  ovulation 
often  follows  menstruation  and  may  occur  between  the  menses ; 
that  the  ovarian  changes  which  precede  ovulation  by  producing 
ovarian  tension,  reflexly  excite  the  uterus  and  cause  menstruation  ; 
that  both  processes  are  under  some  nervous  control,  yet  either  may 
occur  independently." 

It  would  appear,  then,  that  the  relation  existing  between  ovula- 
tion and  menstruation  is  not  definitely  determined,  but  that  they 
are  intimately  associated  cannot  be  questioned,  for  the  removal  of 
the  ovaries,  as  a  rule,  is  followed  by  a  discontinuance  of  men- 
struation. 

As  to  the  relation  between  a  particular  menstrual  period  and 
the  process  of  ovulation,  Marshall  says,  that  the  decidua  of  a 
particular  menstrual  period  is  related  not  to  the  ovum  discharged 
at  that  period,  but  to  the  ovum  discharged  at  the  preceding  period, 
and  which  takes,  probably,  a  week  in  its  passage  from  the  ovary 
to  the  uterus. 

Formation  of  Corpus  Luteum. — After  an  ovum  has  been  dis- 
charged from  a  Graafian  follicle  certain  changes  take  place 
in  the  latter  structure  which  result  in  the  formation  of  a  corpus 
luteum.  The  cavity  of  the  follicle  is  filled  with  blood  from  the 
lacerated  blood-vessels  of  the  walls  of  the  follicle,  and  this  under- 
goes coagulation,  the  serum  being  expressed  and  absorbed,  and  the 
clot,  at  first  red,  later  becomes  decolorized.  Into  this  penetrates  the 
tunica  interna  of  the  theca  folliculi,  which  undergoes  proliferation. 
In  this  proliferated  tissue  are  lutein  cells  containing  lutein,  which 
gives  the  characteristic  yellow  color  from  which  the  corpus  luteum 
derives  its  name,  and  fibrous  connective  tissue  with  blood-vessels 
whose  capillaries  penetrate  between  the  lutein  cells.  The  inner  wall 
of  the  corpus  luteum  becomes  folded  in  or  convoluted,  and  the  cen- 
tral portion  of  this  body  undergoes  degeneration  and  is  absorbed. 
Afterward  the  corpus  luteum  undergoes  hyaloid  degeneration, 
and  the  corpus  albicans  results,  so  called  because  of  the  white 
color  which  replaces  the  yellow.  This  is  ultimately  absorbed,  and 
there  remains  but  a  small  amount  of  connective  tissue. 

While  a  corpus  luteum  which  occurs  during  menstruation  exists 


650 


REPRODUCTIVE  ORGANS. 


for  but  a  few  weeks,  that  which  occurs  in  connection  with  preg- 
nancy remains  for  a  much  longer  period,  even  until  after  child- 


FIG.  434.— Portions  of  ova  of  Asterias  glacialis,  showing  changes  affecting  the 
germinal  vesicle  at  the  beginning  of  maturation :  a,  germinal  vesicle  ;  b,  germinal 
spot,  composed  of  nuclein  and  paranuclein  (c) ;  d,  nuclear  spindle  in  process  of 
formation  (Hertwig).  V 


, — pv 


FIG.  435. — Formation  of  polar  bodies  in  ova  of  Asterias  glacialis:  ps,  polar 
spindle ;  pbf,  first  polar  body  ;  pb",  second  polar  body  ;  n,  nucleus  returning  to  con- 
dition of  rest  (Hertwig). 


FIG.  436. — A,  mature  ovum  of  echinus :  n,  female  pronucleus ;  B,  immature  ovarian 
ovum  of  echinus  (Hertwig). 

birth.     The  manner  of  formation  is,  however,  the  same  in  both, 
only  under  the  stimulus  of  pregnancy  the  corpus  luteum  which 


ERECTION  OF  THE  PENIS.  651 

occurs  at  this  time  becomes  much  larger,  having  a  diameter  of 
from  12  to  20  mm.  The  two  varieties  are  known  respectively  as 
the  corpus  luteum  spurium  or  of  menstruation,  and  the  corpus  luteum 
verum  or  of  pregnancy.  There  is,  however,  no  essential  difference 
between  the  two.  It  was  supposed  at  one  time  that  the  existence 
of  pregnancy  could  be  determined  by  the  presence  of  a  corpus 
luteum  in  the  ovary,  but  the  existence  of  such  bodies  in  undoubted 
virgins  has  overthrown  that  theory  absolutely.  Is  is  said  that  in 
the  mouse  there  is  no  difference  as  to  structure  or  size  between 
corpora  lutea  derived  from  follicles  whose  ova  have  been  impreg- 
nated and  those  whose  ova  have  not  been  fertilized. 

Maturation  of  the  Ovum. — This  process  takes  place  in  all  ova, 
and  is  necessary  for  their  preparation  for  fertilization.  In  other 
words,  an  immature  ovum  is  not  susceptible  of  being  fertilized. 
These  changes  take  place  while  the  Graafian  follicle  is  also  be- 
coming mature,  and  are  complete  by  the  time  the  ovum  is  dis- 
charged from  the  follicle.  To  understand  the  process  thoroughly 
one  must  be  familiar  with  karyokinesis  (p.  28).  It  may,  how- 
ever, here  be  briefly  described  as  beginning  with  the  migration  of 
the  germinal  vesicle  to  the  periphery  (Fig.  434),  the  rupture  of 
the  nucleus,  the  formation  of  the  spindle,  etc.,  and  the  extrusion 
of  the  polar  bodies  (Fig.  435) ;  and  thus  is  formed  a  new  nucleus, 
the  female  pronucleus  (Fig.  436).  If  the  ovum  is  unfertilized,  it 
undergoes  disintegration,  probably  within  eight  days  from  the 
time  it  left  the  ovary  :  but  if  fertilized,  the  female  and  male  pro- 
nuclei,  the  latter  being  derived  from  a  spermatozoon,  fuse  and 
form  a  new  nucleus,  the  segmentation  nucleus. 

Impregnation. — In  order  that  the  ovum  may  be  impregnated 
or  fertilized  the  spermatozoa  must  come  in  contact  with  it  in  the 
generative  passage  of  the  female  ;  or,  more  properly  speaking,  one 
spermatozoon  must,  for  in  the  process  of  fertilization  but  one  of 
these  structures  is  involved.  This  is  preceded  by  erection  of  the 
penis  and  ejaculation  of  the  semen. 

Erection  of  the  Penis. — Any  influence  brought  to  bear  upon 
the  sexual  center,  which  is  situated  in  the  lumbar  region  of  the 
spinal  cord,  by  which  it  is  stimulated,  results  in  the  emission  of 
impulses  through  the  nervi  erigentes.  This  influence  may  come 
from  the  brain  in  the  form  of  mental  impressions,  or  from  stimu- 
lation of  the  sensory  nerve-endings  in  the  penis.  The  efferent 
impulses  which  reach  the  penis  cause  a  relaxation  of  the  muscular 
structure  of  the  trabecula?,  thus  increasing  the  capacity  of  their 
interspaces,  and  also  a  dilatation  of  the  arterial  vessels,  so  that  an 
increased  amount  of  blood  is  supplied  to  the  organ.  The  veins 
(Fig.  437)  which  return  the  blood  from  the  penis  are  relatively 
small,  and  are  unable  to  return  quickly  the  blood  supplied  by  the 
relaxed  arteries ;  this  obstacle  to  the  free  return  of  the  blood  is 
augmented  by  the  compression  of  the  veins  produced  by  the  con- 


652 


REPRODUCTIVE  ORGANS. 


traction  of  the  erector  penis  and  bulbocavernosus  muscles.     The 
result  is  the  distention  of  the  penis  with  blood,  producing  the  rigid 

condition  of  that  organ  called  erec- 
tion. The  verumontanum,  which  like- 
wise contains  erectile  tissue,  becomes 
at  the  same  time  rigid,  and  assisted 
by  the  contraction  of  the  sphincter 
vesicse,  closes  the  passage  to  the 
bladder. 

The  clitoris  of  the  female  pos- 
sesses an  erectile  structure,  and  during 
coitus  undergoes  a  change  analogous 
to  that  of  erection  in  the  male. 

Ejaculation.— Some  writers  de- 
scribe an  ejaculatory  center — that  is, 
a  special  center  in  the  spinal  cord  that 
presides  over  the  emission  of  semen 
which  constitutes  ejaculation,  while 
others  deny  its  existence.  As  a  result 
of  the  excitation  produced  by  the  act 
of  copulation  the  testicles  become  very 
active  in  the  formation  of  their  secre- 
tion, and  this  is  carried  to  the  ampullae 
of  the  vasa  deferentia  by  the  muscular 
action  of  the  various  portions  of  the 
canal  which  it  traverses.  The  mus- 
cular coat  of  the  seminal  vesicles,  and 
that  of  the  ampullations  by  their  con- 
traction expel  their  contents,  the 
semen,  into  the  ejaculatory  ducts, 
through  which  it  is  discharged  into 
the  prostatic  portion  of  the  urethra 
(Fig.  438).  Here  are  added  to  it  the 
secretion  of  the  prostate,  expelled  by 
the  muscular  tissue  of  that  gland,  and 
the  secretion  of  the  glands  of  Cowper. 
By  the  combined  rhythmic  action 
of  the  ischio-  and  bulbocavernosi,  constrictor  urethra,  external 
sphincter  ani,  and  levator  ani  muscles,  the  semen  is  forced  through 
the  remaining  part  of  the  urethra  and  out  of  the  meatus. 

During  copulation  the  glands  of  Bartholin,  situated  on  each 
side  of  the  commencement  of  the  vagina  and  behind  the  hymen, 
and  which  are  regarded  as  the  analogues  of  Cowper's  glands  in 
the  male,  secrete  a  mucous  fluid  which  is  poured  out  upon  the 
vulva. 

By  the  vibratile  movement  of  their  tails  or  flagella  the  sper- 
matozoa penetrate  the  os  uteri,  passing  into  the  interior  of  the 


FIG.  437. — Deep  dorsal  vein 
and  its  tributaries :  A,  glaus  ;  B, 
B',  corpus  cavern osum  ;  (7,  section 
of  pubis,  made  slightly  below  the 
symphysis.  1,  Deep  dorsal  vein ; 

2,  its  origin  behind  the  glans  ;  3, 

3,  its   tributaries    coming    from 
the     corpus     cavernosum     and 
corpus     spongiosum ;     4,     dorsal 
vein,  bifurcated  and  arranged  in 
a  sort  of  plexus,  subpubic  plexus ; 
5,  plexus  of  Santorini ;  6,  7,  an- 
astomosis   of    superficial    dorsal 
vein   with   external    pudic    and 
obturator  (Testut). 


EJACULATION. 


653 


uterus.  According  to  Litzmann  and  others,  at  the  time  of  coitus 
the  uterine  muscular  tissue  contracts,  thus  compressing  the  cavity 
of  that  organ ;  subsequently  relaxation  occurs  and  by  aspiration, 
the  spermatozoa  are  drawn  into  the  cavity.  Kristeller  believes 
that  at  the  time  of  the  completion  of  coitus,  when  the  orgasm 
occurs,  the  plug  of  mucus  in  the  cervical  canal  is  forced  down  into 
the  vagina,  and  that  the  spermatozoa,  discharged  at  the  same 
moment,  attach  themselves  to  it  and  are  drawn  back  with  it  into  the 


FIG.  438. — Posterior  portion  of  urethra,  seen  after  median  incision  of  the  ante- 
rior wall  of  the  canal ;  1,  vesical  neck ;  2,  section  of  prostate  and  urethral  sphincters ; 
3,  section  of  membranous  urethra;  4,  section  of  spongy  urethra;  4',  bulb;  5,  5',  cor- 
pora cavernosa ;  6,  verumontanum  with  orifice  of  utricle ;  7,  posterior  wall  of 
prostatic  urethra  with  its  glandular  openings ;  8,  right  ejaculatory  duct  laid  bare, 
with,  8',  its  opening;  9,  Cowper's  gland;  10,  its  excretory  duct  laid  bare;  1CX, 
opening  of  this  duct;  11,  longitudinal  fold  of  mucous  membrane  of  urethra;  12, 
cul-de-sac  of  bulb;  13,  collar  of  bulb  (Testut). 

uterus.  Whether  either  of  these  theories  is,  in  the  main,  the  cor- 
rect one  has  not  been  determined.  That  the  spermatozoa  can,  by 
the  vibratile  motion  alone  of  their  tails  or  flagella,  penetrate  the  os 
uteri  is  proved  by  the  fact  that  impregnation  has  occurred  when 
the  woman  was  unconscious.  The  rate  at  which  spermatozoa  travel 
in  the  human  female  passages  is  one  centimeter  in  three  minutes ; 
in  the  rabbit  two  and  three-quarter  hours  are  sufficient  for  them  to 
reach  the  ovary.  Their  vitality  is  retained  in  the  human  passages 


654  REPRODUCTIVE  ORGANS. 

probably  for  several  days  and  sometimes  longer,  after  which  they 
undergo  disintegration.  Diihrssen  found  living  spermatozoa  in  a 
tube  which  he  removed  from  a  woman  whose  statement,  if  true, 
would  show  that  they  had  been  there  for  fully  a  month. 

Ovarian  and  Abdominal  Pregnancy. — The  portion  of  the 
female  generative  passages  in  which  the  spermatozoa  and  the 
ovum  ordinarily  meet  is  probably  the  Fallopian  tube  in  the  major- 
ity of  instances.  It  may,  however,  also  be  the  uterus. 

That  the  place  of  meeting  may  also  be  the  ovary  is  proved  by 
the  occurrence  of  ovarian  pregnancy,  which  is  one  form  of  ectopic 
gestation.  The  proportion  of  ectopic  to  uterine  gestations  is  vari- 
ously estimated ;  some  writers  placing  it  at  1  in  500,  and  others  at 
1  in  10,000.  Of  ectopic  pregnancies,  Edgar  thinks  4.8  per  cent,  are 
ovarian.  Williams  regards  only  5  reported  cases  of  primary  ova- 
rian pregnancy  as  having  been  conclusively  demonstrated,  30  cases 
as  highly  probable,  and  25  as  fairly  probable.  Four  cases  are 
reported  by  such  competent  authorities  as  Leopold,  Patenko,  and 
Martin.  It  may  be  interesting  in  this  connection  to  say  that  in 
Patenko's  case  the  right  ovary,  which  was  about  the  size  of  a  hen's 
egg,  contained  a  cyst  within  which  was  a  yellow  body  consisting  of 
cylindrical  and  flat  bones,  which  upon  examination  were  found  to 
be  fetal,  and  not  such  as  are  found  in  dermoid  cysts.  In  the  wall 
around  the  cyst  were  found  corpora  lutea  and  Graafian  follicles, 
showing  that  the  tissue  was  true  ovarian  tissue.  Martin  reports  2 
cases  which  he  regards  as  undoubtedly  primary  ovarian  pregnancies  ; 
1  of  these  is  shown  in  Fig.  439.  He  believes  that  in  cases  of  ova- 
rian pregnancy  the  spermatozoon  finds  its  way  through  the  fimbri- 
ated  extremity  of  the  Fallopian  tube  into  one  of  the  small,  recently 
ruptured,  cysts  so  often  seen  on  the  surface  of  the  ovary,  and  there 
fertilizes  the  contained  ovum. 

As  to  the  occurrence  of  primary  abdominal  or  peritoneal  preg- 
nancy, there  is  great  difference  of  opinion.  Some  writers,  while 
recognizing  its  possibility,  doubt  that  it  has  ever  actually  occurred. 
When  the  impregnated  ovum  is  implanted  upon  the  fimbria  ovarica 
the  subsequent  growth  would  make  it  appear  to  be  a  peritoneal  or 
abdominal  pregnancy.  SchlechtendahFs  case  would,  however, 
appear  to  have  been  an  instance  of  primary  abdominal  pregnancy. 
In  this  case  a  fetus  15  cm.  long  was  found  attached  to  the  abdomi- 
nal wall,  near  the  spleen,  of  a  woman  who  had  died  from  hemor- 
rhage. Should  this  form  of  pregnancy  occur,  it  would  be  explained 
by  the  meeting  of  the  spermatozoa  and  the  ovum  at  the  time  of  the 
escape  of  the  latter  from  the  Graafian  follicle,  which,  instead  of 
entering  the  Fallopian  tube,  falls  into  the  peritoneal  cavity,  where 
it  would  subsequently  become  developed. 

Webster,  in  his  Ectopic  Pregnancy,  in  which  he  considers  the 
subject  most  exhaustively,  states  it  as  "  extremely  probable  that 


OVARIAN  AND  ABDOMINAL  PREGNANCY. 


655 


no  gestation  can  begin  its  development,  except  in  some  part  of 
the  genital  tract  derived  from  the  Miillerian  ducts  which  form  the 
uterus  and  tubes."  This,  of  course,  rules  out  both  abdominal  and 
ovarian  pregnancy.  Of  the  latter,  Webster  says :  "  Supposed 
cases  of  ovarian  pregnancy  require  to  be  studied  carefully,  and  in 
every  instance  must  be  distinguished  from  the  following  condi- 
tions, which  may  be  mistaken  for  it,  viz.,  pregnancy  in  the  outer 


FIG.  439. — Prof.  August  Martin's  case  of  ovarian  pregnancy.    The  intact  tube  is 
seen  lying  above  the  ovarian  sac  containing  the  fetal  envelopes. 

end  of  the  tube  which  has  become  intimately  connected  with  the 
ovary ;  pregnancy  in  an  accessory  tube-end  which  has  become 
attached  to  it ;  pregnancy  in  the  ovarian  fimbria,  which  may  be 
hollow  sometimes,  representing  the  extreme  outer  end  of  the  tube  ; 
pregnancy  in  the  tube  which  has  extended  into  the  ovarian  sac 
of  peritoneum,  which  occasionally  occurs  in  women." 

The  terms  "  extra-uterine  pregnancy  "  and  "  ectopic  pregnancy  " 
are  ordinarily  used  synonymously,  but  there  is  really  a  distinction. 

The  term  "ectopic"  implies  that  the  gestation  is  outside  the 
uterine  cavity.  A  gestation  may  occur  in  that  part  of  the  Fallo- 
pian tube  which  is  situated  in  the  uterine  wall.  Such  an  one, 
described  under  the  name  "  interstitial"  would  not  be  "  extra- 
uterine,"  for  it  is  within  the  uterus.  It  would,  however,  be  "  ec- 
topic." If  the  view  of  Webster  is  correct,  all  ectopic  gestations 
must  be  of  tubal  origin.  He  divides  them  into  five  subdivisions  : 
1.  Ampullar,  in  which  the  gestation  begins  in  the  ampulla  or  mid- 
dle portion  of  the  tube,  and  he  regards  this  as  by  far  the  most 
common.  2.  Interstitial,  in  which  the  gestation  develops  in  that 


656 


REPRODUCTIVE  ORGANS. 


portion  of  the  tube  situated  in  the  wall  of  the  uterus.  3.  Infundib- 
ular, in  which  the  gestation  develops  in  the  outer  end  of  the  tube- 
lumen  or  among  the  fimbriae.  4.  Anomalous  Varieties. — Among 
these  Webster  places  those  that  develop  in  accessory  fimbriated 
extremities  or  in  tubal  diverticula,  and  also  those  that  develop  in 
detached  portions  of  Mullerian  tissue— i.  e.,  those  attached  to  or 
embedded  in  the  ovary.  In  this  class,  he  thinks,  are  some  of  the 
recently  described  cases  of  ovarian  pregnancy.  5.  Cornual  preg- 
nancy, in  which  the  ovum  develops  in  the  undeveloped  horn  of  a 
bicornate  uterus. 


FIG.  440. — Sections  of  the  ovum  of  a  rabbit,  showing  the  formation  of  the  blasio- 
dermic  vesicle :  a,  6,  c,  d,  are  ova  in  successive  stages  of  development ;  sp,  zona  pel- 
lucida  ;  ect,  ectomeres,  or  outer  cells ;  ent,  entomeres,  or  inner  cells  (E.  Van  Beneden). 

Method  of  Fertilisation. — In  the  vitelline  membrane  of 
the  ova  of  some  animals  there  is  a  minute  opening,  the  micropyle, 
by  which  a  spermatozoon  gains  access  to  the  interior.  Such  an 
opening  does  not  exist  in  the  human  ovum.  Some  histologists 
have  described  the  vitelline  membrane  as  possessing  a  porous 
structure,  and  it  has  been  suggested  that  through  one  of  these 


FORMATION  OF  EMBRYO.  657 

pores  a  spermatozoon  might  pass.  It  is  by  no  means  established 
that  such  pores  exist.  However,  in  some  way  the  spermatozoon 
passes  through  the  membrane  into  the  protoplasm ;  here  its  tail 
disappears  and  the  head  assumes  a  spherical  form,  and  to  it  the 
name  of  "  male  pronucleus  "  is  given.  The  male  and  female  pro- 
nuclei  then  unite  to  produce  the  fecundation  nucleus.  After  this 
occurs  the  ovum  consists  of  a  mass  of  protoplasm  with  a  nucleus, 
and  is  spoken  of  as  the  "  segmentation  sphere,"  because  it  under- 
goes segmentation. 

Segmentation. — This  consists  in  the  production  of  two  seg- 
ments by  the  same  process  of  indirect  division  which  takes  place 
in  the  germinal  vesicle ;  these  again  divide,  forming  four,  and,  the 
same  process  continuing,  the  entire  ovum  is  broken  up  into  a  mass 
of  spherical  cells  which,  from  the  resemblance  to  a  mulberry,  is 
named  morula.  These  cells  separate  into  two  layers,  with  fluid 
between  them,  except  at  one  place  where  the  layers  are  in  con- 
tact. The  blastodermic  vesicle  is  now  formed.  It  is  probable 
that  development  has  reached  this  stage  at  about  the  tenth  day, 
by  which  time  the  ovum  has  entered  the  uterus.  The  albuminous 
secretion  of  the  Fallopian  tube  serves  as  pabulum  or  food  to  the 
cells  in  this  process. 

Formation  of  Embryo. — The  next  change  which  takes  place 
is  the  formation  of  three  layers  from  the  two  just  described.  They 
are  termed  the  epiblazt,  the  mesoblast,  and  the  hypoblast;  together 
they  form  the  blastoderm.  The  epiblast  is  most  external,  in  con- 
tact with  the  vitelline  membrane,  which  takes  no  part  in  the 
changes  thus  far  described. 

It  would,  perhaps,  be  too  much  to  say  that  the  embryo  is  now 
formed,  yet  the  subsequent  changes  are  but  the  modification  and 
differentiation  of  the  cells  which  compose  these  three  layers.  The 
epiblast  forms  the  brain  and  spinal  cord,  portions  of  the  organs  of 
special  sense,  and  the  epidermis,  and  also  takes  part  in  the  for- 
mation of  the  chorion  and  amnion.  The  mesoblast  forms  the 
vascular,  osseous,  and  muscular  systems,  and  the  endothelium 
which  lines  the  serous  cavities.  The  hypoblast  forms  the  lungs, 
the  epithelium  of  the  alimentary  canal  and  of  the  glands  which 
are  offshoots  from  this  canal.  The  membrane  which  lines  the 
allantois  and  the  yolk-sac  is  also  formed  from  the  hypoblast. 

The  segmentation  just  described  is  such  as  takes  place  in  the 
human  ovum  and  that  of  other  mammalia.  It  is  a  process  in 
which  the  entire  mass  of  protoplasm  undergoes  division :  such 
ova  are  said  to  be  holoblastic.  In  the  ova  of  birds  and  of 
reptiles  only  a  portion  undergoes  this  segmentation,  the  rest  serv- 
ing as  food.  Such  ova  are  meroblastic.  As  an  illustration  of  the 
latter  may  be  mentioned  the  fowl's  egg,  in  which  the  processes  of 
development  have  been  most  thoroughly  studied.  In  this  egg 
only  a  minute  portion,  the  cicatricula,  becomes  converted  into 

42 


658  REPRODUCTIVE  ORGANS. 

the  chick,  while  the  great  body  of  material  nourishes  the  growing 
embryo  until  it  leaves  the  shell  and  is  able  to  gain  its  own  liveli- 
hood. As  such  an  embryo  is  never  attached  to  the  parent,  it  must 
have  within  itself,  supplemented  by  what  it  receives  from  the  air, 
all  the  material  necessary  for  its  development  and  maintenance 
until  freed  from  its  enclosing  shell,  hence  the  large  size  of  the 
ovum  ;  while  in  the  mammal  this  supply  is  not  necessary,  for  the 
attachment  to  the  maternal  structures  is  made  at  an  early  period 
of  its  history,  and  from  the  parent  all  necessary  sustenance  is 
obtained. 

Inasmuch  as  development  has  been  so  much  more  thoroughly 
studied  in  the  hen's  egg  than  in  any  other,  and  inasmuch  as  the 
processes  are  in  many  respects  probably  the  same  as  in  the  human 
ovum,  the  development  of  the  chick  will  be  described,  referring 
to  the  principal  points  of  difference  as  they  are  reached  in  the 
description,  giving,  however,  only  a  general  view  of  the  subject, 
which  is  much  too  extensive  and  complicated  to  discuss  in  any 
other  manner  in  this  connection,  and  referring  our  readers  for 
fuller  details  to  monographs  on  embryology. 

Development  of  Chick. — If  the  shell  of  a  hen's  egg  is 
broken  during  the  first  day  of  its  incubation  and  the  blastoderm 
is  examined,  it  will  be  seen  that  there  is  a  clear  central  portion, 
the  area  pellucida,  and  a  portion  outside  of  this,  the  area  opaca, 
which  is  much  less  clear.  The  embryo  forms  in  the  area  pellu- 
cida, and  the  membranes  and  structures  which  are  to  nourish  it 
form  in  the  area  opaca.  On  the  second  day,  the  area  opaca  having 
meanwhile  extended,  within  it  are  formed  red  blood-corpuscles 
and  vessels,  and  during  the  same  time  in  the  area  pellucida  the 
heart  is  formed.  These  structures  arise,  as  has  been  stated,  from 
the  cells  of  the  mesoblast. 

At  one  extremity  of  the  area  pellucida  a  fold  forms  in  the  blas- 
toderm, and,  as  this  is  the  anterior  end,  it  is  called  the  cephalic 
fold.  A  similar  fold,  the  tail  fold,  forms  at  the  other  extremity 
of  the  area  pellucida.  In  the  same  manner  lateral  folds  form  on 
the  sides.  All  these  folds,  which  include  the  three  layers  of  the 
blastoderm,  approach  one  another  below,  and  by  so  doing  form  a 
canal,  the  embryonal  sac.  This  sac  is  bounded  above  by  the 
blastoderm,  anteriorly  by  the  cephalic  fold,  posteriorly  by  the  tail 
fold,  and  laterally  by  the  lateral  folds,  while  below  it  is  in  com- 
munication with  the  vitellus.  This  embryonal  sac  subsequently 
becomes  divided  into  two,  one  division  forming  the  alimentary 
tract,  and  the  other  the  body-walls,  the  umbilicus  being  the  point 
at  which  the  folds  all  unite.  These  folds  just  described  are  to  be 
carefully  distinguished  from  the  membranes,  the  amnion,  the  cho- 
rion,  etc.  The  folds,  as  stated,  involve  the  epiblast,  the  mesoblast, 
and  the  hypoblast,  while  in  the  formation  of  the  membranes  the 
various  layers  play  different  parts. 


MEMBRANES  OF  THE  EMBRYO- AMNION. 


659 


Membranes  of  the  Embryo. — Amnion. — The  mesoblast 
about  the  embryo  splits  into  two  laminae,  the  parietal  and  the 
visceral.  The  parietal  (external)  joins  with  the  epiblast  to  form 
the  somatopleure,  from  which  the  amnion  and  the  body-walls  are 
developed,  while  the  visceral  lamina  unites  with  the  hypoblast  to 


JVC 


F.So. 


FIG.  441. — Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo 
chick :  N.  C.,  neural  canal ;  Ch,  notochord ;  D,  foregut ;  F.  So,  somatopleure  ;  F.  8p, 
splanchnopleure ;  Sp,  splanchnopleure  forming  the  lower  wall  of  the  foregut;  Ht, 
heart ;  pp,  pleuroperitoneal  cavity ;  Am,  amniotic  fold ;  A,  epiblast ;  B,  mesoblast ; 
C,  hypoblast  (Foster  and  Balfour). 

form  the  splcmchnopleure.  From  this  structure  are  developed  the 
walls  of  the  allantois,  the  yolk-sac,  and  the  alimentary  canal. 
Between  the  somatopleure  and  the  splanchnopleure  is  the  pleuro- 
peritoneal cavity,  which  later  is  divided  by  partitions  into  peri- 
cardial,  pleural,  and  peritoneal  cavities.  From  the  somatopleure 
folds  form  which  rise  above  the  embryo  on  all  sides,  meeting  over 


hy 


FIG.  442.— Diagrammatic  longitudinal  section  of  a  chick  on  the  fourth  day:  ep, 
epiblast ;  hy,  hypoblast ;  sm,  somatopleure  ;  vm,  splanchnopleure ;  af,  pf,  folds  of  the 
amnion;  pp,  pleuroperitoneal  cavity;  am,  cavity  of  the  amnion;  ai,  allantois;  a, 
position  of  the  future  anus:  h,  heart;  i,  intestine;  vi,  vitelline  duct;  ys,  yolk;  s, 
foregut ;  m,  position  of  the  mouth ;  me,  the  mesentery  (Allen  Thomson). 

its  back  and  fusing  together.  These  are  the  amniotic  folds.  As 
each  fold  is  double,  when  they  unite  two  membranes  result :  the 
inner,  next  the  embryo,  is  the  amnion,  and  the  outer,  toward  the 
vitelline  membrane,  is  the  false  amnion  (Fig.  442).  The  latter 
and  the  vitelline  membrane  fuse  together,  forming  the  chorion. 


660  REPRODUCTIVE  ORGANS. 

The  true  amnion  has  epiblast  for  its  inner,  and  mesoblast  for  its 
outer,  layer,  and  the  space  between  it  and  the  embryo  is  the 
araniotic  cavity,  in  which  the  liquor  amnii  accumulates. 

Yolk-sac. — The  yolk-sac  is  a  very,  important  structure  in  the 
fowl  and  in  birds  generally,  as  it  is  upon  the  yolk  that  the  nutri- 
tion of  the  embryo  depends  ;  but  in  mammals  it  is  of  little  impor- 
tance, as  the  nutritive  material  in  the  vitellus  is  insignificant  in 
amount. 

Allantois. — The  allantois  is  a  projection  of  the  splanch- 
nopleure  into  the  pleuroperitoneal  cavity.  It  subsequently  com- 
municates with  the  posterior  portion  of  the  intestinal  canal,  and 
its  lining  is  hypoblast.  This  structure  projects  more  and  more 
into  the  pleuroperitoneal  cavity,  following  up  the  folds  that  have 
been  described  as  forming  the  true  and  the  false  amnion.  The 
allantois  at  last  comes  in  contact  with  the  chorion,  which,  it  will 
be  remembered,  \vas  formed  by  the  fusion  of  the  false  amnion 
with  the  vitelline  membrane,  and  into  the  villi  of  that  structure  it 
sends  processes.  It  is  especially  developed  in  that  part  corre- 
sponding to  the  attachment  of  the  ovum  to  the  uterine  wall.  The 
allantois  has  two  layers,  a  mesoblastic  and  a  hypoblastic.  In  the 
former  are  blood-vessels  which  come  from  the  vascular  system  of 
the  embryo,  the  connecting  vessels  becoming  the  umbilical  arteries. 
At  a  later  stage  of  development  the  character  of  the  allantois  dis- 
appears, except  in  that  portion  which  is  to  be  included  within  the 
body  of  the  fetus,  and  which  becomes  the  urinary  bladder,  and  in 
that  portion  between  the  bladder  and  the  umbilicus,  which  becomes 
the  urachus. 

Chorion. — This  membrane,  as  already  stated,  is  formed  by 
the  union  of  the  vitelline  membrane  and  the  false  amnion.  When 
first  formed,  it  is  smooth,  but  becomes  shaggy  by  the  growth  from 
it  of  processes  called  villi.  These  villi  are  at  first  scattered  over 
the  whole  exterior  of  the  ovum,  but  later  they  are  found  only  at 
the  point  of  attachment  of  the  ovum  to  the  uterus,  where 'the 
placenta  is  to  be  formed.  In  these  villi  are  blood-vessels  from  the 
fetal  vascular  system. 

Placenta. — When  the  impregnated  ovum  reaches  the  cavity 
of  the  uterus  the  mucous  membrane  of  that  organ  is  prepared  to 
receive  it,  and  it  finds  a  lodgment  there.  Under  the  stimulus  of 
impregnation  the  whole  mucous  membrane  becomes  thickened,  and 
at  the  termination  of  uterogestation  the  entire  mucous  membrane 
of  the  body  is  cast  off;  it  is  called  the  decidua  vera.  Especially 
marked  is  this  thickening  at  the  point  of  attachment  of  the  ovum, 
and  to  this  part  the  name  decidua  serotina  is  applied  (Fig.  443). 
As  a  result  of  this  stimulus  the  mucous  membrane  increases  around 
the  ovum,  finally  completely  enclosing  it.  This  new  formation  is 
the  decidua  reflexa. 

The  villi  of  the  chorion  find  their  way  into  the  depressions  of 


CIRCULATION  IN  THE  EMBRYO. 


661 


the  decidua  serotina,  and  their  walls  become  atrophied,  being  finally 
represented  only  by  epithelial  cells  covering  the  capillary  blood- 
vessels which  have  come  from  the  allantois.  The  blood-vessels 
in  the  decidua  serotina  become 
converted  into  blood-spaces, 
sinuses,  to  which  the  uterine 
arteries  carry  blood,  and  from 
which  the  uterine  veins  carry 
the  blood  away.  It  will  be  seen, 
therefore,  that  the  fetal  blood- 
vessels are  surrounded  by  the 
maternal  blood  in  the  uterine 
sinuses,  the  two  fluids  being 
separated  only  by  the  thin  wall 
of  the  fetal  capillaries,  through 
which  the  interchanges  of  oxygen 
and  carbon  dioxid  take  place, 
and  also  the  passage  of  the  nutri- 
tious material  to  supply  the 
growing  fetus,  and  in  the  reverse 
direction  pass  the  effete  products 
to  be  eliminated.  The  structure 
which  performs  all  these  im- 
portant offices  is  the  placenta, 
made  up  of  both  maternal  and 
fetal  tissues.  It  seems  hardly 
necessary  to  say  that  the  blood 
of  the  mother  and  that  of  the 
child  never  come  in  contact, 
but  are  always  separated  by  the  walls  of  the  fetal  capillaries. 

At  birth  the  placenta  is  cast  off,  arid  by  the  contraction  of  the 
uterine  muscular  tissue  the  mouths  of  the  maternal  blood-vessels 
are  closed,  and  thus  hemorrhage  is  prevented.  The  blood  which 
escapes  during  a  normal  labor  is  that  which  was  in  the  sinuses. 
The  functions  of  the  placenta  are  thus  seen  to  be  threefold — nutri- 
tive, respiratory,  and  excretory. 

Circulation  in  the  Embryo.— Vitelline  Circulation.— During 
the  earliest  part  of  human  fetal  life  the  contents  of  the  ovum 
supply  the  growing  embryo  with  nutrition.  This  is  done  by 
means  of  vessels  which  compose  the  vitelline  circulation,  but,  im- 
portant as  this  circulation  is  in  the  fowl's  egg,  it  is  of  very  brief 
duration  in  the  human  subject,  for  the  supply  of  nutritious 
material  is  soon  exhausted,  probably  at  the  sixth  week. 

Placental  or  Fetal  Circulation  (Fig.  444). — By  the  sixth  week 
the  placenta  is  formed  and  the  connection  has  been  made  by  which 
the  embryo  receives  its  nourishment  from  the  maternal  blood. 


4  5 

FIG.  443. — Series  of  diagrams  repre- 
senting the  relationship  of  the  decidua 
to  the  ovum  at  different  periods.  The 
decidua  are  colored  black,  and  the  ovum 
is  shaded  transversely.  In  4  and  5  the 
vascular  processes  of  the  chorion  are 
figured.  1,  Ovum  entering  the  con- 
gested mucous  membrane  of  the  fundus 
—decidua  serotina;  2,  decidua  reflexa 
growing  around  the  ovum ;  3,  comple- 
tion of  the  decidua  around  the  ovum ; 
4,  general  growth  of  villi  of  the 
chorion  ;  5,  special  growth  of  villi  at 
placental  attachment,  and  atrophy  of 
the  rest  (copied  from  Dalton). 


662 


REPRODUCTIVE   ORGANS. 


From  this  time  until  birth  the  fetus  depends  upon  the  piacental  or 
fetal  circulation  for  its  nourishment  and  maintenance. 

The  blood  of  the  fetus  is  freed  from  much  of  its  impurities  in 
the  placenta,  and  there  likewise  it  receives  oxygen  and  nutritive 
materials.  It  returns  to  the  fetus  through  the  umbilical  vein, 
passing  to  the  liver.  In  this  organ  the  current  is  divided  :  the 


Vmbilicus- 


Placenta, 


FIG.  444.— Diagram  of  the  fetal  circulation. 

greater  part  joins  with  the  venous  blood  of  the  portal  vein ;  a 
second  portion  goes  directly  into  the  hepatic  circulation ;  while  a 
third  part  goes  through  the  ductus  venosns  into  the  ascending 
vena  cava  without  passing  through  the  liver.  The  currents  all 
meet  again  in  the  ascending  vena  cava,  here  mixing  with  the  blood 
returning  from  the  lower  extremities.  The  ascending  vena  cava 


CHANGES  IN  THE  CIRCULATION  AT  BIRTH.  663 

discharges  its  blood  into  the  right  auricle  of  the  heart,  where, 
guided  by  the  Eustachian  valve,  it  is  directed  into  the  left  auricle 
through  the  foramen  ovale.  From  this  cavity  it  passes  into  the 
left  ventricle,  thence  into  the  aorta,  which  distributes  it  to  the 
head  and  upper  extremities.  It  will  be  seen  from  this  description 
that  to  these  three  portions  of  the  body  the  blood  from  the 
placenta  is  distributed.  This  blood  is  not  very  pure,  for  it  is 
deteriorated  by  admixture  with  the  impure  blood  returning  from 
the  lower  extremities,  with  which  it  mingles  in  the  ascending 
vena  cava;  but  it  is  the  purest  and  most  nutritious  blood  the 
fetus  receives,  and  this  accounts  for  the  greater  development  of 
the  upper  portion  of  the  body  as  compared  with  the  lower,  which 
is  so  striking  a  feature  in  the  newborn  babe. 

The  blood  returns  from  the  head  and  upper  extremities  through 
the  descending  vena  cava  to  the  right  auricle,  and  thence  passes 
into  the  right  ventricle.  There  is  probably  always  a  slight  mixing 
of  the  currents  in  the  right  auricle,  that  returning  from  the 
placenta  and  that  from  the  descending  vena  cava,  but  at  first  this 
is  very  slight ;  later,  it  is  doubtless  greater.  From  the  right 
ventricle  the  blood  passes  into  the  pulmonary  artery,  a  very  small 
portion  going  through  the  capillaries  of  the  lungs,  the  larger  part 
passing  through  the  cluctus  arteriosus  into  the  aorta,  passing  down 
this  vessel  to  the  common  and  internal  iliacs,  from  which  latter 
are  given  off  the  hypogastric  or  umbilical  arteries  by  which  the 
blood  is  conveyed  to  the  placenta. 

By  comparing  this  description  with  that  of  the  circulation  in 
the  adult  the  points  of  difference  will  be  seen.  It  may  be  well 
to  note  here  that  there  are  six  principal  points  of  difference  be- 
tween the  fetal  and  the  adult  circulatory  apparatus,  besides  less 
important  ones  of  size  and  shape.  These  points  of  difference  are 
the  presence  in  the  fetal  heart  of  the  Eustachian  valve  and  the 
foramen  ovale,  in  the  venous  system  of  the  umbilical  vein  and  the 
ductus  venosus,  and  in  the  arterial  system  of  the  umbilical  arteries 
and  the  ductus  arteriosus. 

Changes  in  the  Circulation  at  Birth. — During  intra- 
uterine  life  the  respiratory  center  in  the  medulla  is  supplied  with 
blood  containing  sufficient  oxygen  to  prevent  any  inspiratory  im- 
pulse, and  there  is  therefore  during  this  period  no  attempt  at 
respiration  on  the  part  of  the  fetus.  As  soon,  however,  as  the 
connection  between  the  parent  and  the  child  is  severed,  whether 
by  separation  of  the  placenta  or  by  tying  of  the  umbilical  cord, 
the  respiratory  center,  being  no  longer  supplied  with  oxygen,  sends 
out  impulses  to  the  respiratory  muscles,  and  respiration  begins. 
This  may  be  hastened  or  assisted  by  slapping  the  skin  or  dashing 
water  upon  it,  but  under  ordinary  circumstances  these  measures 
are  not  called  for.  The  fact  that  respiration  will  take  place  while 
the  fetus  is  still  enclosed  in  its  membranes,  without  the  reflex  in- 


664  REPRODUCTIVE  ORGANS. 

fluence  of  exposure  to  the  air,  shows  that  this  is  not  the  essential, 
but  only  a  contributing,  cause.  It  is  the  stoppage  of  the  placenta! 
circulation  which  starts  the  respiratory  movements. 

Although  during  fetal  life  some  blood  flows  through  the  pulmo- 
nary capillaries,  still  the  amount  is  small,  and,  there  being  no  air 
in  the  pulmonary  alveoli,  the  lungs  will  sink  if  placed  in  water. 
The  first  respiratory  movement  causes  an  enlargement  of  the 
thoracic  cavity  and  a  consequent  distention  of  the  lungs,  the  air 
passing  h  to  the  alveoli,  and  the  blood,  which  is  at  the  time 
in  the  pulmonary  capillaries,  becomes  oxygenated  and  returns  to 
the  left  auricle  as  arterial  blood.  The  expansion  of  the  thorax 
reduces  the  resistance  to  the  flow  of  the  blood  through  the  pulmo- 
nary circulation,  and  as  a  result  a  large  amount  of  blood  goes  to 
the  lungs ;  this  means  a  lessened  amount  through  the  ductus 
arteriosus,  and,  following  the  law  that  a  diminution  of  function  is 
followed  by  atrophy,  this  vessel  begins  to  diminish  in  size,  and 
becomes  closed  between  the  fourth  and  tenth  days,  and  in  later 
life  is  to  be  found  as  a  fibrous  cord  between  the  left  pulmonary 
artery  and  the  aorta. 

With  the  termination  of  the  placental  circulation  the  flow 
through  the  ductus  venosus  ceases,  and  within  a  few  days  this 
vessel  closes,  and  remains  only  as  a  fibrous  cord  in  the  fissure  of 
the  same  name  in  the  liver :  that  portion  of  the  umbilical  vein 
which  is  within  the  body  of  the  child  becomes  the  round  ligament 
of  the  liver.  The  blood  flowing  into  the  right  auricle  from  the 
inferior  vena  cava  finds  it  easier  to  pass  into  the  right  ventricle 
than  into  the  left  auricle,  which  is  now  filled  with  blood  from  the 
lungs,  and  hence  takes  this  course,  while  the  blood  cannot  flow 
into  the  right  auricle  through  the  foramen  ovale  by  reason  of  the 
valve  which  has  been  forming  in  the  left  auricle  during  the  latter 
part  of  intra-uterine  life  to  close  this  opening.  The  opening  is 
not  permanently  closed  for  a  considerable  time  after  birth,  in  some 
cases  a  year,  and  sometimes  not  at  all.  As  a  result  of  these 
various  changes  the  fetal  circulation  becomes  converted  into  that 
of  the  adult. 


INDEX. 


ABDOMFSJJL  reflex,  480 
Abducens,  521 

paralysis  of,  521 
Aberration,  chromatic,  573 

spherical,  573 
Abrin,  113 
Abscissa,  452 
Absolute  humidity,  376 
Absorption  of  food,  167,  254 
Accommodation,  560,  564 

convergence  in,  570 

negative,  565 

positive,  565 

pupil  contraction  in,  570 

range  of,  569 

Schoen's  theory  of,  569 

Tseherning's  theory  of,  568 
Accommodative  rest,  564 
Acenrulus  cerebri,  351 
Achromatic  spindle,  28,  29 
Achromatic.  _ 
Achroodextrin,  97 
Achylia  gastrica,  219 
Acid  sodium  phosphate  in  urine,  83 
Acid-albumin,  109 
Acromegaly, 
Actinic  rays,  538 
Adamantoblast-. 
Adam's  apple,  354 
Addison's  disease,  349 
Adenoid  tissue,  37 
Adipocere,  99 
Adipose  tissue,  35 

vesicles,  35 
Adrenal  bodies,  347 
Adrenalin,  349 
Aerotonometer,  385 
Afferent  nerves,  462 

vessels,  425 
After-images,  596 
After-vibration,  elastic,  453 
Agglutinins,  301 

bacterial,  301 
Agminated  glands,  226 
Air.  amount  of  moisture  in,  376 

and  blood,  interchange  of  oxygen  and 
carbon  dioxid  between,  383 

calorimeters,  412 

expired. 

vitiated,  breathing  of,  379 
Air-cells,  363 


Air-space,  381 
Albumin,  107 
acid-,  109 
alkali-,  109 
coagulation  of,  107 
derived,  109 
egg-,  108 
nucleo-,  112 
precipitation  of,  107 
serum-,  108 
Albuminates,  109 
Albuminoids,  115 

action  of  gastric  juice  on,  199 
Albuminous  glands,  174 
Albuminuria,  438 
alimentary,  260 
Albumosuria,  438 
Alcohol,  absorption  of,  from  stomach, 

161 

as  food,  166 
effect  on  body,  158 
on  brain,  162 
on  digestion,  159 
on  excretion  of  uric  acid,  161 
on  gastric  acidity,  160 

digestion,  159* 
on  liver,  162 
on  secretion  of  gastric  juice,  159 

of  saliva,  159 
on  temperature,  165 
gastric  absorption  of,  255 
Alcoholic  beverages,  157 

influence  on  excretion  of  uric  acid. 

161 

purin-bodies  in,  157 
Alexin,  300 

Alimentary  album  in  uria,  260 
bolus,  186 
canal,  168 

walls  of,  659 
glycosuria,  256,  438 
Alkali-albumin,  109 
Alkaline  carbonates,  83 
phosphates,  82 
tide,  432 
Allantois,  660 
walls  of,  659 

Alloxuric  substances  in  urine,  437 
Amacrine-cells,  551 
Ambon,  603 
Ameba,  24 

665 


666 


INDEX. 


Ameboid  movements,  24 
Ameloblasts,  55 
Ametropia,  571 
Amido-acetic  acid,  247 
Amido-ethylsulphonic  acid,  247 
Amidulin,  96 
Ammonia,  86 
Ammonium  salts,  86 
Amnion,  659 
Amphiaster,  30 
Ampho-peptones,  199 
Amplitude,  623 

definition  of,  622 
Ampulla,  628 
Ampullae,  144 
Amygdaline  leukemia,  289 
Amylodextrin,  96 
Amylopsin,  97,  235 
A  my  loses,  95 
Anabolism,  120 

definition  of,  25 
Anacrotic  wave,  328 
Anatomy,  definition  of,  20,  21 
Anelectrotonic  current,  466 
Anelectrotonus,  467 
Angle  of  vision,  563 
Animal  gum,  112 
Ankle-clonus,  480 
Anode,  444 
Anospinal  center,  482 
Anterior  chamber  of  eye,  554 

horn,  cells  of,  474 

median  fissure,  471 

white  commissure,  471 
Anterolateral  fissure,  471 
Antrum ,  634 

pylori,  194 
Anvil- bone,  703 
Aortic  pressure,  mean,  321 

valve,  308 

Apertura  scalse  vestibuli  cochleae,  607 
Apex-beat,  315,  317 
Aphasia,  511 
Apical  foramina,  50 
Apnea,  388 
Apoplexy,  501 
Apparatus,  definition  of,  19 
Aquseductus  cochleae,  609 

vestibuli,  607 
Aqueous  humor,  554 
chemistry  of,  556 
Arborization,  67,  72 
Areolae,  144 

primary,  48 

secondary,  49 
Areolar  tissue,  34 
Arnold's  ganglion,  520 
Aromatic  substances  in  urine,  439 
Arterial  pressure,  321 
Arteries,  308 

bronchial,  364 

circulation  of,  318 


Arteries,  rate  of  flow  in,  323 
Aryteno-epiglottic  fold,  354,  358 
Arytenoid  cartilages,  354 
Arytenoideus  muscle,  356 
Ascending  tract,  473 
Asphyxia,  389 
Assimilation,  120 

definition  of,  25 
Association-fibers,  506,  507 
Aster,  30 
Astigmatism,  572 
Ataxy,  cerebellar,  492 
Atrium  of  lungs,  364 
Atrophy,  senile,  84 
Attic  recess,  605 
Attraction-particle,  28 
Audi  phone,  618 
Auditory  area,  512 

canal,  external,  598,  599 

nerve,  523,  615 
Auricle,  598 

left,  306 

right,  306 
Auricular  diastole,  312 

septum,  308 

systole,  312 

Automatic  centers,  486 
Axial  cord,  64 

space,  64 

stream,  319 
Axis-cylinder,  64 

process,  71,  72, 73 
Axis-fibrils,  64 
Axolemma,  64 
Axon,  71 
Azygos  vein,  364 

BACILLARY  layer  of  retina,  552 
Bacterial  agglutinins,  301 

digestion,  253 

poison,  114 

Bactericidal  property  of  serum,  300 
Bacteriolysis,  300 
Bartholin's  duct,  174,  654 
Bartley's  use  of  Fehling's  test,  88 
Basal  ganglia,  499 

functions  of,  502 
Basic  sound  of  heart,  316 
Basophils,  289 
Baths,  420 
Battery,  444 
Beer,  157 

Belly-sweetbread,  346 
Bernard's   experiment   to    prove   irrita- 
bility of  muscle,  442 

glycogenic  theory,  258 
Beverages,  156 

as  food,  158 
Bicuspids,  171 
Bile,  244 

antiseptic  powers  of,  250 

constituents  of,  245 


INDEX. 


667 


Bile,  offices  of,  249 

properties  of,  244 
Bile-acids,  247 
Bile-canaliculi,  242 
Bile-duct,  common,  243 
Bile-pigments,  246 

Gmelin's  test  for,  246 
Bile-salts,  247 

tests  for,  248 
Biliary  passages,  intercellular,  242 

plexus,  interlobular,  242 
Bilicyanin,  247 
Bilirubin,  246 
Biliverdin,  246 
Binocular  vision,  583 
Birch-modification  of  Young-Helm holtz 

color  theory,  592 
Birth,  circulation  »t,  663 
Biuret  reaction,  103 
Bladder,  429 
Blastoderm,  657 

folds  of,  658 
Bleeders,  296 
Blind  spot,  549,  576 
Blindness,  color-,  593 
Blood,  268 

amount     expelled     from     ventricle, 
314 

and  air,   interchange  of   oxygen  and 
carbon  dioxid  between,  383 

and  tissues,  oxygen  and  carbon  dioxid 
interchange  between,  386 

changes  in,  from  respiration,  381 

circulation  of,  305,  311 
time  for,  325 

coagulation  of,  294 
causes,  296 
influences  hastening,  296 

retarding,  295 
theories,  297 

distribution  of,  270 

gravity  and,  330 

inert  layer  of,  319 

internal  friction  of,  319 

lakey,  269 

menstrual,  power  to  clot,  296 

microscopic  structure  of,  270 

movements  of,  in  diastole,  313 
in  systole,  313 

peripheral  resistance  to,  319 

physical  properties  of,  268 

regeneration  of,  299 

serum,  294 

specific  gravity  of,  268 
Blood-cells,  286 
Blood-corpuscles,  270 

colorless,  288.     See  also  Leukocytes. 

red,  270.     See  also  Red  Corpuscl-es. 

white,  288.     See  also  Leukocytes. 
Blood-flow,  rate  of,  323 
Blood-glands,  334 


Blood-plasma,  291 

enzymes  of,  292 

extractives  of,  292 

gases  in,  294 

inorganic  salts  in,  294 

proteids  of,  292 

water  of,  291 
Blood-plates,  291 
Blood-pressure,  319 

aortic,  321 

arterial,  321 

measuring  of,  321 

negative,  323 

venous,  323 
Blood-stains,  precipitins   in  identifying, 

301 

Bolus,  alimentary,  186 
Bone,  41 

blood-vessels  of,  44 

calcium  phosphate  in,  84 

cancellated,  41 

chemical  composition  of,  44 

compact,  41 

development  of,  45 

lacuna?,  42 

lamella?,  42 

lymphatic  vessels  of,  44  ' 

nerves  of,  44 
Bone-corpuscles,  42 
Bone-marrow,  43 
Bowman's  capsule,  422 

glands,  531 

membrane,  542 
Brace,  Julia,  case  of,  535 
Brain,  483 

columns  of,  485 

effect  of  alcohol  on,  162 

gray  matter  of,  483 

pyramids  of,  485 

weight  of,  483 
Brain-sand,  351 
Bran,  154 
Brandy,  157 
Bread,  154 

Break  of  current,  447 
Bridgman,  Laura  D.,  case  of,  528 
Brigham's  case   of    esophago-duodenos- 

tomy,  217 

Broca's  convolution,  511 
Bromelin,  155 
Bronchi,  362 
Bronchial  arteries,  364 

tube,  lobular,  363 

veins,  364 
Bronchiole,  363 
Broth,  meat,  152 
Bruch's  membrane,  544 
Brunner's  glands,  225 
Buffy  coat,  295 
Bulb,  484 
Burdach's  column,  474 


668 


INDEX. 


CADAVERIC  rigidity,  62,  456 
Caflein,  156 
Caffeo-tannic  acid,  156 
Cajal's  cells,  551 
Calcification,  40 
Calcium  carbonate,  85 

fluorid  in  body,  86 

phosphate  in  body,  84 

salt  in  body,  84 
Calculi,  salivary,  182 
Calorie,  409 
Calorific  rays,  588 
Calorimetry,  410 
Canaliculi/42,  597 
Cane-sugar,  93 

action  of  gastric  juice  on,  199 

as  food,  123 
Canines,  55,  171 
Capillaries,  310 

pulmonary,  364 

rate  of  flow  in,  325 
Carbamid,  432 
Carbo-hemoglobin,  281 
Carbohydrates,  87 

action  of  gastric  juice  on,  199 

as  food,  123 

gastric  absorption  of,  254 

glycogen  formation  from,  257 

intestinal  absorption  of,  255 
Carbon  dioxid  in  body,  87 

and  oxygen  interchange.     See  Oxy- 
gen and  Carbon  Dioxid. 

tension  of,  in  blood,  384 
Carbonates  in  body,  83.     See  also   Cal- 
cium, Sodium,  etc. 
Carbon-monoxid  hemoglobin,  280 

spectrum  of,  286 
Cardia,  191 
Cardiac  cycle,  311 

glands,  193 

impulse,  315 

innervation,  317 

muscle,  61 

composition  of,  63 

nerves,  318,  525     . 

orifice,  191 

portion  of  stomach,  movements  of,  203 
Cardio-accelerator  center,  481,  487 
Cardiogram,  312 
Cardiograph,  312 
Cardioinhibitory  center,  487 
Cardiopneumatic  movements,  383 
Carotid  gland,  352 
Cartilage,  38 

articular,  39 

cellular,  41 

chemical  composition  of,  41 

costal,  40 

hyaline,  38 

inorganic  solids  of,  41 

intermediate,  49 

organic  solids  of,  41 


Cartilage,  transitional,  39 

true,  38 

white  fibrous,  40 

yellow  elastic,  41 
Casein,  112 

pancreatic,  238 

vegetable,  155 
Caseinogen,  109,  112 
Casper's  cystoscope,  428 
Caudate  nucleus,  499 
Cell  stations,  488 
Cell-group,  middle,  474 
Cells,  23 

air-,  363,  364 

amacrine-,  551 

bipolar,  70 

blood,  286.      See  also  Red,  Corpuscles 
and  Leukocytes. 

bone-forming,  43 

central,  193 

chief,  193 

columnar,  531 

connective-tissue,  35 

crescentic,  175 

daughter-,  625 

dentin-forming,  50 

division  of,  28 

fat-,  35 

fiber-,  of  Eetzius,  610 

giant-,  44 

glia-,  73 

goblet-,  31 

granule,  35 

gustatory,  538 

hair-,  of  ear,  615 

lamellar,  35 

marrow-,  44,  287 

mastoid,  605 

mother-,  625 

mucus-secreting,  32 

multipolar,  70 

nerve-,  69 

neuroglia,  73 

of  anterior  horn,  474 

of  Cajal,  551 

of  Deiter5,  615 

of  gray  matter  of  cerebrum,  504 

of  posterior  horn,  474 

of  Purkinje,  491 

olfactory,  531 

oxyntic,  193 

parietal,  193 

plasma-,  35 

salivary,  changes  in,  180 

spermatogenic,  625 

spider-,  73 

splenic,  44 

sustentacular,  336,  538,  625 

tendon-,  38 

unipolar,  70 

villi,  224 
Cellulose,  98 


IXDEX. 


669 


Cellulose,  action  of  ptyalin  on,  183 
Cement,  tooth,  53 
Central  canal,  471 

cells,  193 

lobe,  498 

of  cerebrum,  487 

spindle,  28 

vein,  241 

Centrifugalization,  270 
Centrosome,  25 
Centrosphere,  28 
Cephalic  fold,  658 
Cereals  as  food,  153 
Cerebellar  ataxy,  492 

tracts,  473 
Cerebellum,  491 

effect  of  removal  of,  492 

functions  of,  492 

gray  matter  of,  491 

impressions  of,  sources  of,  493 

inferior  peduncles  of,  486 

laminse  of,  491 

white  matter  of,  491 
Cerebral  localization,  509 
Cerebrin,  75 
Cerebrosides,  75 
Cerebrospinal  fluid,  471 
Cerebrum,  495 

convolutions  of,  496 

fibers  of,  506 

fissures  of,  496 

functions  of,  507 

gray  matter  of,  496 

microscopy  of,  503 

gyri  of,  496 

lobes  of,  497 

microscopy  of,  503 

peduncles  of,  499 

sulci  of,  496 

vital  importance  of,  507 

white  matter  of,  505 
Cerumen,  417,  599 
Charcot's  crystals,  630 
Chemistry,  definition  of,  20 

physiologic,  21,  76 
Cheyne-Stokes  respiration,  387 
Chick,  development  of,  658 
Chief  cells,  193 
Cholalic  acid,  247 
Cholesterin,  101,  248,  266 
Choletelin,  247 
Cholic  acid,  247 
Chondrigen,  115 
Chondrin,  41 
Chorda  tympaui,  177 
Chordse  tendinese,  307 
Choriocapillaris,  544 
Chorion,  660 
Choroid,  544 
Chromatin,  25 
Chromogen,  348 
Chromoplasm,  25 


hronographs,  450 
Chyle,  305 
Chymosin,  112 
Cilia,  33 
Ciliary  body,  547 

ganglion,  520 

ligament,  544,  546 

motion,  33 

muscle,  546 

processes,  545 
Ciliospinal  center,  481 
Cineritious  matter,  69 
Circulation,  311 

pulmonary,  311 

systemic,  311 

time  required  for,  325 
Circulatory  system,  305 
Circulus  iridis  major,  546 

minor,  546 

Circumvallate  papillae,  536 
Clarke's  column,  474 
Claustrum,  499,  505 
Climacteric,  645 
Climate,  menstruation  and,  645 
Clitoris,  erection  of,  652 
Coagulated  proteid,  108,  113 
Coagulum,  143* 
Coccygeal  gland,  352 
Cochlea,  607 

canals  of,  609,  612 

duct  of,  609 

nerve  of,  615 

spiral  canal  of,  608 
Cocoa,  156 
Coffee,  156 

Coffin-lid  crystals,  441 
Cohnheim's  areas,  57 
Cold-blooded  animals,  406,  407 
Collagen,  115 

Colliculus  nervi  optici,  549 
Colloids,  106 
Color,  587 

diagram,  588 

theories,  591,  592 
Color-blindness,  593 
Colorimetric  equivalent,  411 
Colors,  complementary,  588 

physiologic  mixture  of,  590 
Colostrum,  141 
Colostrum-corpuscles,  145 
Columella,  608 
Columnar  carneee,  307 
Columnar  cells,  529 
Columns,  Burdach's,  474 

Clarke's,  474 

Goll's,  473 

of  brain,  485 

spinal,  471 
Comma  tract,  474 
Cornmissural  fibers,  506 
Commissures,  471 
Commutator,  448 


670 


INDEX. 


Complement,  300 
Complementul  air,  374 
Conduction-paths  in  cord,  477 
Cone  proper,  553 
Cone-bipolars,  551 
Cone-elements,  553 
Cone-fiber,  553 
Cone-foot,  552 
Cone-granules,  .552 
Cones,  552 
Conical  papillae,  537 
Conjunctiva,  597 
Conjunctiva!  reflex,  480 
Connective  tissue,  34 

jelly-like,  38 
Consonants,  394 
Continuous  spectrum,  283 
Contractile  substance,  56 
Contractility,  442 
Contraction,  secondary,  458 

superposition  of,  454 

vermicular,  457 
Contraction-remainder,  453 
Corium,  413 
Cornea,  541 

chemistry  of,  555 

proper,  substance  of,  542 

vascular  system  of,  542 
Corneal  corpuscle,  542 

spaces,  542 

Cornicula  laryngis,  354 
Cornua,  471 

Corona  radiata,  500,  634 
Corpora  cavernosa,  630 

quadrigemina,  501 

striata,  499 
Corpus  albicans,  649 

Arantii,  308 

callosum,  495 

dentatum,  491 

luteum,  formation  of,  651 

spongiosum,  630 
Corpuscles,  bone-,  42 

colostrum-,  145 

connective-tissue,  35 

corneal,  542 

Pacinian,  65 

salivary,  181 

tactile,  65 

Vater's,  65 

Corresponding  points,  583 
Coil  ex.  microscopy  of,  503 
Cortical  substance,  496 
Corti's  membrane,  615 

organ,  613,  614 

rods,  614 

Costal  cartilages,  366 
Coughing  center,  486 
( 'owner's  glands,  431 
Cowrf  milk,  142 
(  ninial  nerves,  513 
Creatinin  in  urine,  438 


Cremasteric  reflex,  479 

Cretinism,  341 

Crico-arytenoideus  lateralis  muscle,  356 

posticus  muscle,  356 
Cridoid  cartilage,  354 
Cricothyroid  muscle,  356 
Crista  acustica,  610,  612 

vestibuli,  607 
Crotalin,  114 
Crowd-poison,  377 
Crura  cerebelli,  491 

cerebri,  499 
Crusta,  499 

petrosa,  53 
'  phlogistica,  295 
Crystallin,  111,  556 
Crystalline  lens,  554 
capsule  of,  555 
chemistry  of,  556 
Crystalloids,  106 
Cubic  space  allotment,  381 
Cuneiform  cartilages,  354 
Cupola,  608 
Curd,  112,  143 
Current  of  action,  458 

of  injury,  458 

of  rest,  458 
Cuticle,  413 
Cylindrical  glasses,  572 
Cystic  duct,  242 
Cystoscope,  428 
Cytotoxins,  301 

DALTONISM,  593 
Daniell  cell,  444 
Daughter-cells,  625 
Decidua  reflex  a,  660 

serotina,  660 

veia,  660 

Defecation,  265-268 
Degeneration,  473 
Deglutition,  186-190 

center,  486 
Deiters' cells,  615 

phalanges,  615 
Demarcation  current,  458 
Demilunes  of  Heidenhain,  174 
Demours'  membrane,  542 
Dendrites,  69,  72 
Dendrons",  72 
Dental  follicle,  54 

germ,  common,  54 

lamina,  54 

papilla,  54 

pulp,  50 

sac,  54 

Denticulate  lamina,  612 
Dentin,  50,  51 
Dentinal  tubuli,  51 
Deprez  electric  signal,  451 
Derma,  413 
Descemet's  membrane,  542 


INDEX. 


671 


Descending  tract,  473 
Detrusor  urinae  muscle,  429 
Deutero-proteoses,  19V) 
Deutoplastic  granules,  637 
Dextrose,  87 

fermentation  of,  91 

in  urine,  439 
Diabetes,  459 

mellitus,  259,  439 
Dialysis,  106 
Diapedesis,  288,  290 
Diaphragm,  367 

iris,  560 
(Master,  30 
Diastole,  312 
Diastolic  sound,  316 
Diathesis,  hemorrhagic,  297 
Dicrotic  pulse,  329 

wave,  328,  329 
Diet,  age  and,  140 

meat,  vegetable,  128 

proper,  127 

tropical,  135 
Diffusion,  104 
Digastric  muscle,  355 
Digestion,  167 

apparatus  of,  168 

bacterial,  253 

effect  of  alcohol  on,  159 

inlarge  intestine,  251 

intestinal,  221 

mouth,  169 

stomach,  191.    See  also  Stomach  Diges- 
tion. 

tryptic,  236 
Diplopia,  583 
Direct  cell  division,  28 
Disaccharids,  93 
Disassimilation,  definition  of,  25 
Discus  proligerus,  634 
Dispersion,  574 
Dispirem,  29 

Distance,  judgment  of,  584 
Dobie's  line,  58 
Dromograph,  324 
Dropsy,  305 

Drugs,  effect  on  muscle-curve,  456 
DuBois-Reymond  key,  445 

inductorium,  447 
Ductless  glands,  334 
Ductus  auditorius,  cochlearis,  613 

choledochus,  243 

endolymphaticus,  607,  610,  611 
Dulong's  calorimeter,  410 
Duodenal  glands,  225 
Duodenum,  221 

Dysentery  from  drinking  water,  122,  123 
Dyspnea,  389 

EAR,  598 
external,  598 
hair-cells  of,  615 


Ear,  internal,  607 

labyrinth  of,  607 

middle,  600 

ossicles  of,  602.     See  also  Ossicles. 

vestibule  of,  607 
Ear-stones,  610 
Ear-wax,  417,  599 
Ebner's  glands,  537 
Ectopia  vesicse,  428 
Edema,  305 
Efferent  nerves,  462 

vessels,  425 
Egg-albumin,  108 
Eggs  as  food,  149 
Egg-tubes,  635 

Ehrlich's  lateral-chain  theory,  291 
Ejaculation,  652 
Elastic  tissue,  37 
Elasticity,  definition  of,  37 
Elastin,  116 
Electric  keys,  444 

phenomena  of  muscle,  442,  457 

signal  of  Deprez,  451 
Electrodes,  444 

non-polarizable,  447 
Electrotonus,  465 
Eleidin,  117 
Elementary  tissues,  23 
Embolism,' 300 
Embryo,  circulation  of,  661 

formation  of,  657 

membranes  of,  659 
Embryologic     method   of    determining 

course  of  nerve-fibers,  473 
Emergency  ration,  131 
Emmetropia,  570 
Emulsification,  101 

Emulsion  theory  of  fat-absorption,  261 
Enamel,  53 
Enamel-jelly,  55 
Enamel-organ,  54,  55 
Enamel-prisms,  53 
Enamel-pulp,  55 
Encephalon,  483 
End-bulbs,  65 

Endocardiac  pressure,  recording  of,  313 
Endocardium,  305 
Endolymph,  609 
i  Endomysium,  58 
j  End-organs,  motor,  61,  65 
j  Endosmosis,  102 
Endothelium,  30 
End-plate,  65 
English  ration,  131 
Enterokinase,  119,  228 
Enzymes,  117-119,  292 

spleen  as  producer  of,  339 
Eosinophiles,  289 
Epiblast,  657 
Epicardium,  305 
Epidermis,  413 
Epiglottis,  354 


672 


INDEX. 


Epiglottis  in  deglutition,  188 
Epimysium,  58 
Epinephrin,  349 
Epineurium,  04 
Epiphysis  cerebri,  351 
Epithelium,  30 

ciliated,  32 

columnar,  cylindric,  31 

cubical,  30  ' 

germinal,  31,  631 

glandular,  32 

pavement,  scaly,  30 

simple,  stratified,  34 

spheroidal,  32 

transitional,  34     • 
Epitympanic  recess,  605 
Epoophoron,  638 
Equilibrium,  493-495 
Erectile  center,  482 
Erection,  651 
Erythroblasts,  44,  287 
Erythrodextrin,  97,  183 
Esophageal  glands,  188 
Esophago-duodenostomy,  217 
Esophago-enterostomy,  212 
Esophagus,  188 
Ether,  581 

glyceric,  99 
Eupnea,  388 

Eustachian  tube,  306,  604 
Excretin,  266 
Excretoleic  acid,  266 
Exophthalmic  goiter,  341 
Exosmosis,  105 
Expiration,  371-374 
Expiratory  center,  386 
Expired,  air,  377 
External  capsule,  499 

oblique,  371 

rectus,  557 

functions  of,  559 
Extrinsic  muscles  of  tongue,  186 
Eye,  541 

accommodation  of,  560,  564 

anterior  chamber  of,  554 

appendages  of,  597 

chemistry  of,  555 

effects  of  facial  paralysis  on,  522 

near-sighted,  571 

normal,  570 

posterior  chamber  of,  554 

reduced,  562 

schematic,  562 

tunics  of,  541 

white  of,  541 
Eyeball,  muscles  of,  556 
Eyes,  convergence  of,  during  accommo- 
dation, 570 

FACIAL  expression,  522 
nerve,  521 
paralysis,  522 


Fallopian  tubes,  640 

ova  in,  644 
Falsetto,  393 
Far-point,  569,  570 
Fasciculi,  58 
Fasciculus  of  Tiirck,  473 
Fat-cells,  35 

Fatigue  of  muscles,  cause  of,  455 
Fats,  99 

absorption  of,  261 

action  of  gastric  juice  on,  199 

as  food,  125 

course  of   from  columnar  epithelium 
to  lacteals,  263 

disposition  of,  264 

gastric  absorption  of,  255 

glycogen  formation  from,  257 
Fatty-acid  theory  of  fat  absorption,  263 
Feces,  265 

after  stomach  removal,  214 

color  of,  266 

composition  of,  266 

quantity  of,  265 

reaction  of,  266 
Fecundation  nucleus,  657 
Fehling's  test  for  dextrose,  88 
Female  genital  organs,  631 
Fenestra  ovalis,  605 

rotunda,  606 
Fermentation,  91,  117 
Fermentation-test  for  dextrose,  88 
Ferments,  117-119 
Ferratin,  Schmiedeberg's,  240 
Fertilization,  651 

method  of,  656 
Fetus,  circulation  of,  661 

at  birth,  663 
Fibrils,  57 
Fibrin,  110 
Fibrin-ferment,  297 
Fibrin-globulin,  293 
Fibrinogen,  110,  293 
Fibrinoplastin,  110,  297 
Fibrocartilage,  40 
Fibrous  nervous  matter,  63 

tissue,  38 
Field  ration,  132 
Filiform  papillae,  537 
Filtration-and-difl'usion  theory  of  lymph 

origin,  303 

Filum  terminale,  478 
First  sound,  316 
Fission,  28 

Fissures  of  spinal  cord,  471 
Floor-space,  allotment  of,  381 
Flour,  processes  of  making,  154 
Focus,  inability  to,  514 
Focussing,  560 
Food,  121 

absorption  of,  167,  254 

definitions  of,  158 

digestibility  of,  130,  209 


INDEX. 


673 


Food  for  soldiers,  131 

quantity  required,  130 
of  water  in,  79 

sodium  chlorid  in,  81 

starch  in,  96 
Food-stuffs,  121 

composition  of,  148 

inorganic,  absorption  of,  in  stomach, 
254 

oxidation  of,  409 
Foramen  of  Sommering,  548 

ovale,  308 
Forebrain,  483 
Form,  appreciation  of,  583 
Fossa  vesicalis,  242 
Fovea  centralis,  548 

hemi-elliptica,  607 

hemispherica,  607 
Fracture,  green-stick,  84 
Franklin  color  theory,  592 
Fraunhofer  lines,  284 
Frick's  spring  myograph,  323 
Frontal  lobe,  497 
Function,  definition  of,  17 
Functions,  classification  of,  21 
Fungiform  papillae,  537 
Funiculi,  64 
Funiculus  cuneatus,  485,  486 

gracilis,  485,  486 

of  Rolando,  485,  486 
Furfur-aldehyd,  248 
Furfurol,  248 
Fuscin,  556 

GALACTOSE,  88,  92 

Gall-bladder,  242 

Gamgee's  theory  of  HC1  in  gastric  juice, 

196 
Ganglia,  72 

automatic  menstrual,  647 
basal,  499 

functions  of,  500 
cerebral,  499 
of  trigeminus,  520 
spinal,  476 

function  of,  483 
Ganglion  spirale,  609,  615 
Garrison  ration,  133 
Giirtner's  duct,  638 
Gastric  acidity,  intestinal  contents  and, 

214 

juice,  action  of,  199 
artificial,  220 
gerrnicidal  powers  of,  197 
hydrochloric  acid  in,  195 
mixed  with  saliva,  195 
pepsin  in,  198 

pepsin-hydrochloric  acid  in,  198 
quantity  of,  194 
rennin  in,  198 

secretion  of  alcohol  and,  159 
nerves,  524 


Gastritis  glandularis  atrophicans,  219 
Gelatin,  115 
Gelatoses,  200 
Gemmation,  28 
Geniohyoid  muscle,  356 
Genital  organs,  624 
female,  631 
male,  625 

Genitospinal  center,  481 
Gerlach's  nerve-network,  475 
German  ration,  131 
Germinal  epithelium,  631 

spots,  638 

vesicle,  637,  638 
Giant-cells,  44 
Gland-pulp,  332 
Glans  penis,  630 
Glia-cells,  73 
Glisson's  capsule,  239 
Globulicidal  action  of  serum,  292,  300 
Globulins,  81,  110,  276 
Glossopharyngeal  nerve,  388,  523 
Glottis,  358,  360 

in  singing,  395 

movements  of,  373 
Glucoses,  87 
Glucosid,  260 
Gluteal  reflex,  479 
Gluten,  153 
Glycerids,  99 
Glycocoll,  247 
Glycogen,  97,  257 

action  of  ptyalin  on,  183 
Glycogenic  theory,  257 
Glycosuria,  259 

alimentary,  256,  439 

from  pancreas,  removal,  239 
Gmelin's  reaction,  247 
Goblet-cell,  31 
Goiter,  341 
Golgi's  organ,  69 
Goll's  column,  473 
Gowers'  hemacytometer,  271 

hemoglobinometer,  278 
Graafian  follicles,  633 
bursting  of,  643 
ova  in,  635 
Granule-cells,  35 
Granuloplasm,  24 
Grape-sugar,  87 
Graves'  disease,  341 
Grave-wax,  99 

Gravity,  circulation  and,  330 
Gray  commissure,  471 

fibers,  64 

matter,  69 

nerve-fibers  of,  474 
of  brain,  483 
of  cerebellum,  491 
of  cerebrum,  496 

microscopy  of,  503 
of  cord,  473 


674 


INDEX. 


Green-stick  fracture,  84 
Ground-bundle,  anterolateral,  473 
Gum,  animal,  112 
Gustatory  cells,  538 

nerve,  517 

pore,  538 
Gyri,  496 

operti,  498 

HAIR-CELLS  of  ear,  615 

Hairs,  417 

Hammarsten's  blood-coagulation  theory, 

297 

Hamulus,  609 
Harmonic  series,  622 
Hasner's  valve,  597 
Hassal's  corpuscles,  347 
Haversian  canals,  41,43 
Head,  motor  area  of,  511 
Hearing,  598 

physiology  of,  616 

theories  of,  618 
Heart,  305 

apex-beat  of,  315,  317 

beat  of,  explanation  of,  317 

impulse  of,  315 

movements  of,  311 

papillary  muscles  of,  307 

parietal  portion,  305 

pause  of,  312 

septum  of,  306 

shortening  of,  315 

sounds,  316 

valves  of,  307 

visceral  portion,  305 
Heat-rigor,  111 
Heat-unit,  409 
Heidenhain's  demilunes,  175 

lymph  theory,  303 
Heister's  valve,  244 
Helicotrema,  609 
Heller's  test,  438 
Helmholtz  phakoscope,  568 
Hemacytometer,  271-273 
Hemagglutinins,  301 
Hematin,  276,  281,  282 

hydrochlorid,  281 
Hemato-aerometer,  385 
Hematoblasts,  291 
Hematocrit,  270,  271 
Hematoidin,  246,  282 
Hematopoiesis,  287 
Hematoporphyrin,  282,  431 
Hematoscope,  285 
Hemm,  281 
Hemiplegia,  491 
Hemochromogen,  276,  282 
Hemoglobin,  286 

carbon-monoxid,  280 
spectrum  of,  286 

derivatives  of,  280 
spectra  of,  282 


Hemoglobin,  nitric-oxid,  281 

spectra  of,  282-285 
Hemoglobinometer,  276-278 
Hemolysis,  300 
Hemophilia,  297 
Hemorrhagic  diathesis,  297 
Hemoscope,  285 
Henle's  loop,  422 
Hensen's  line,  57 
Hepatic  artery,  241 

duct,  242 

Hepatin,  Zaleski's,  240 
Hering  color  theory,  588 
Hermann's  hematoscope,  285 
Hetero-proteose,  199 
Hindbrain,  483 
Hippuric  acid  in  urine,  437 
Histohematins,  282 
Histology  of  body,  definition  of,  21 
Holmgren  test,  590 
Homoiothermal  animals,  407 
Horns  of  cord,  474 
Human  milk,  141 
Humidity,  376 
Humor,  aqueous,  554 
chemistry  of,  556 

vitreous,  554 

chemistry  of,  556 
Hyaloid  membrane,  554 
Hyaloplasm,  24 
Hydrobilirubin,  247,  431 
Hydrochloric  acid  in  body,  87 
Hydrogen,  86 

sulphuretted,  86 
Hydrolysis,  119 
Hypermetropia,  571 
Hyperpnea,  389 
Hypoblast,  657 
Hypoglossal  nerve,  526 
Hypophysis  cerebri,  351 

IDENTICAL  point?,  583 
Iliocostalis  muscle,  370 
Immunity,  290 

Ehrlich's  lateral-chain  theory  of,  291 
Impregnation,  651 

method  of,  656 
Incisors,  53,  171 
Inco-ordination,  492 
Incus,  603 

Indifferent  point,  467 
Indirect  cell-division,  28 
Indol,  266 

Indoxyl  in  urine,  439 
Induced  current,  446 
Induction  apparatus,  447 
Inferior  maxillary  nerve,  516 

oblique,  558 

rectus,  557 

functions  of,  559 
Infundibula  of  lungs,  364 
Infundibulum,  640 


INDEX. 


675 


Inhibition  of  reflex  action,  479 
Inorganic,  definition  of,  18 

ingredients,  77 
Inosit,  93 
Insalivation,  172 
Inspiration,  372,  374 

extraordinary  muscles  of,  369,  372 

forced,  374 

muscles  of,  369,  372 

ordinary,  muscles  of,  367 
[nspiratory  center,  386 

spasm,  389 
Insula,  497,  498,  500 
Intensity,  621,  623 
Interarytenoid  fold,  359 
Intercentral  nerves,  463 
Intercostal  muscles,  368 

spaces,  365 
Interlobular  arteries,  425 

plexus,  241 

vein,  241 

Intermediolateral  tract,  474 
Internal  capsule,  499 

medullary  lamina,  501 

oblique,  371 

rectus,  557 
functions  of,  559 

secretion,  335 

sphincter,  227 
Internodes,  64 
Interposed  bundle,  69 
Intervertebral  disks,  365 
Intestinal  contents,  gastric  acidity  and, 
214 

digestion,  221 

juice,  228 

Intestine,  large,  absorption  by,  264' 
digestion  in,  253 
movements  of,  250 
structure  of,  227 

small,  221 

absorption  by,  255 
movements  of,  250 
villi  of,  22-2 

Intra-epithelial  plexus,  544 
Intranuclear  network,  25 
Intraocular  images,  580 
Intrinsic  muscles  of  tongue,  186 
Invertin,  93,  228 
Invert-sugar,  92,  93 
Involuntary  muscle,  61-63 
Involution,  definition  of,  62 
lodin  in  body,  86 

test  for  starch,  96 
lodo-thyrin,  340 
Iris,  545,  575 

arteries  of,  546 

diaphragm,  o60 
Iron  in  body,  86 
Irradiation,  574 
Irritability,  442 
Irritants,  442,  443 


Island  of  Keil,  497,  498,  500 

Iso-electric,  definition  of,  457 

Isomaltose,  95 

Isotonic  solution,  269 

Isthmus  of  fauces,  constrictors,  of,  187 

Ivory  of  tooth,  41 

JACOB'S  membrane,  558 
Jecorin,  240 

Jelly-like  connective  tissue,  38 
Judgment,  508 

KARYOKINESIS,  28 
Karyomitosis,  28 
Katabolism,  120 

definition  of,  25 
Katacrotic  wave,  328 
Katelectrotonic  current,  466 
Katelectrotonus,  467 
Kathode,  444 
Keratin,  117 
Keys,  electric,  444 
Kidney,  421 

blood-vessels  of,  424 

effects  of  removal  of,  427 

function  of,  426 

nerve-supply  of,  425 
Kilocalorie,  409 
Kilogramdegree,  409 
Kinases,  119 

Kinesthetic  area,  509,  510 
Knee-jerk,  480 
Kolliker's  membrane,  615 
Kra  use's  end-bulbs,  65 

membrane,  49 
Kymograph,  313 

LABIUM  tympanicum,  612 
Labyrinth,  607-609 
Labyrinthine  impressions,  493 
Lacrimal  apparatus,  597 
Lactalbumin,  109 
Lacteals,  224 
Lactoglobulin,  109,  111 
Lactose,  88,  94 

in  urine,  439 
Lactosuria,  439 
Lacuna?,  bone,  42 
Lakey  blood,  269 
LamelUe,  42,  43 
Lamina  cribrosa,  541 

fusca,  541 

spiralis,  608 

suprachoroidea,  544 

vitrea,  544 

Langley's  ganglion,  177 
Lanolin,  101 
Laryngeal  nerves,  388,  523 

pouch,  359 
Laryngoscope,  390 
Larynx,  354 

blood-supply  of,  360 


676 


ISDEX. 


Larynx,  cartilages  of,  354 

cavity  of,  358 

depressors  of,  355 

elevators  of,  355 

in  singing,  395-406 

interior  of,  358 

muscles  of,  355 

nerves  of,  360 

photography  of,  394 
Latent  period,  452 
Lateral  horn,  474 

Lateral-chain  theory  of  Ehrlich,  291 
Latissimus  dorsi,  369 
Laurent's  polarimeter,  89 
Lecithin,  101,  249 
Legs,  motor  area  of,  510 
Legumin,  155 
Lens,  crystalline,  554.     See  also  (7h/s- 

talline. 

Lenticular  nucleus,  499 
Leukemia,  288,  338 
Leukocytes,  288 

composition  of,  290 

development  of,  291 

functions  of,  290 

spleen  in  production  of,  338 

varieties  of,  289 
Leukocythemia,  288,  338 
Leukocytopenic  phase,  289 
Leukocytosis,  288 
Leukocytotic  phase,  289 
Leukornains,  115 
Leukotoxin,  301 
Leva  tores  costarum,  368 
Levulose,  88,  92 
Lieberkuhn,  follicles  of,  226 
Ligamentum  pectinatum,  542 

spirale,  613 
Light,  576,  581 

polarization  of,  88 

synthesis  of,  588 
Lignin,  98 
Lilienfeld's     blood-coagulation    theorv, 

297 
Limbus,  612 

luteus,  548 

Lime  phosphate  in  body,  84 
Lingual  nerve,  517 

papilla,  536 
Lipase,  292 
Liquor  folliculi,  635 

sanguinis,  291 

Scarpse,  609 
Lissauer's  tract,  473 
Littre"'s  glands  431 
Liver,  239,  240 

effect  of  alcohol  on,  162 

extractives  of,  240 

glycogenic  action  of,  256 

innervation  of,  253 

iron  in,  240 

proteids,  240 


Load,  effect  on  muscle-curve,  455 

Lobules,  362 

Locus  niger,  499 

Loudness,  621 

Ludwig's  theory  of  origin  of  lymph,  303 

Lungs,  362 

blood-vessels  of,  364 

capacity  of,  374 

causes  of  oxygen  and  carbon  dioxid 
interchange  in,  382 

nerves  of,  364 
Lupino-toxin,  113 
Luschka's  gland,  352 
Luscitas,  514 
Lymph,  302 

circulation  of,  334 

office  of,  304 

origin  of,  303 
Lymphagogues,  303 
Lymphatic  duct,  331 

glands,  332,  333 
'  system,  330 
Lymphocytes,  289,  303 
Lymphoid  tissue,  37,  332 
Lymph-path,  332 

Lymph-sinus,  332 

•_  •••*- 

MACULA  acustica,  610 

cribrosa,  607 

lutea,  548,  553,  577 
Magnesium  salts,  86 
Make  of  current,  447 
Male  genital  organs,  625 
Malleus,  602 
Malpighian  capsule.  422 

corpuscles,  336,  337 
Maltodextrin,  97 
Maltose,  88,  94 
Maly's  theory  of  origin  of  HC1  in  gastric 

juice,  *196 
Mammse,  144 
Mammary  glands,  144 
Mammilla,  144 
Manometer,  321 
Marey's  cardiograph,  312 
Marrow,  bone-,  43 

embryonic,  49 

red,  43 

yellow,  43 

Marrow-cells,  44.  287 
Marsh-gas,  86 
Mastication,  171,  517 
Mastoid  antrum,  605 

cells,  605 
Maxillary  nerves,  516 

rampart,  54 

Maximal  pulsation,  322 
Mean  blood-pressure,  321 
Meat  as  food,  150 

cooking  of,  150,  151 
Meatus,  auditory,  external,  598,  599 
internal,  607 


INDEX. 


677 


Meatus  urinarius,  430 
Mecke!' s  ganglion,  520 
Meconium,  266 
Medulla  oblongata,  484-486 
Medullary  artery,  44 

canal,  43 

sheath,  64 

spaces,  49 

Meibomian  glands,  597 
Membrana  basilaris,  598 

flaccida,  602 

granulosa,  634 

limitans  externa,  552 
interna,  550 

pupillaris,  546 

tectoria,  615 

tympani,  600 
in  hearing,  617 
secundaria,  606 
Memory,  508 

Meniere's  disease,  vertigo  of,  495 
Menopause,  645 
Menses,  645 

Menstrual  ganglia,  automatic,  647 
Menstruation,  645 

and  ovulation,  relation  between,  648 

cause  of,  647 

corpus  luteum  of,  649 

cycle  of,  646 

Mercurial  manometer,  321 
Merycism,  486 
Mesoblast,  657 
Mesocephalon,  488 
Metabolism,  120 
Metakinesis,  30 
Methemoglobin,  281 
Metschnikoff's  phagocytosis  theory,  290 
Micropyle,  656 
Micturition,  430 
Midbrain,  483 
Middle  cell-group,  474 
Migration,  external,  645 

internal,  645 

of  leukocytes,  290 
Milk  as  food,  141 

composition  of,  149 

cows',  143 

human,  144 

formation  of,  145 

secretion  of,  nervous  control  of,  146 

transmission  of  disease  by,  143 
Milk-curdling     enzyme     of    pancreatic 

.juice,  238 
Milk-sugar,  94 
Milk-teeth,  55,  171 
Millon's  reaction,  103 
Mitosis,  28 
Mitral  valve,  308 
Modiolus,  608 

central  canal  of,  608 

spiral  canal  of,  609 
Moist  chamber,  451 


Molars,  55, 171 
Monaster,  30 
Monosaccharids,  87 
Morgagni's  ventricle,  359 
Morula,  657 
Moss-fibers,  492 
Mother-cells,  625 
Motion,  paralysis  of,  464 
Motor  area,  509,  510 

end-organs,  61,  65 

lingual  nerve,  526 

oculi,  513 
Mouth,  absorption  in,  254 

digestion,  169 

effects  of  facial  paralysis  on,  522 

floor  of,  186 
Mouth-breathing,  353 
Mucinogen,  180 
Mucins,  117 
Mucin-sugar,  92 
Mucous  glands,  174 

of  mouth,  secretion  of,  181 
of  stomach,  193 
Mucus-secreting  cells,  32 
Mailer's  fibers,  553 

ring  muscle,  544,  546 
Mumps,  173 

Murexid  test  for  uric  acid,  434 
Muscse  volitantes,  580 
Muscle,  blood-vessels  of,  61 

cardiac,  61,  63 

character  of,  effect  on  curve,  455 

electric  phenomena  of,  442,  457 

fatigue,  cause  of,  455 

involuntary,  61-63 

non-striated,  61 

nuclei  of,  58 

of  insects,  58 

phenomena,  442 

plain,  61 

skeletal,  61 

striated,  56,  61,  62 

voluntary,  56 
Muscle-clot,  11 
Muscle-columns,  57 
Muscle-curve,  449,  452,  454 
Muscle-nerve  preparation,  443 
Muscle-plasma,  62 
Muscles,  ocular,  556 
Muscle-spindles,  61,  69 
Muscle-sugar,  93 
Muscular  contraction,  simple,  451 

sense,  529 

tissue,  56 

tone,  456,  481 

Musciili  papillares,  307,  316 
Musculotonic  center,  481 
Mydriasis,  512 
Mydriatics,  576 
Myeloplaques,  44 
Myeloplaxes,  44 
Mylohyoid  muscle,  355 


678 

Myo-albumin,  109 
Myocardium,  305 
Myogen-fibrin,  62 
Myogram,  449 
Myograph,  449 

Trick's  spring,  323 
Myoheraatin,  63 
Myopia,  571 
Myosin,  62,  111 
Myosin-fibrin,  62 
Myosinogen,  111 
Myotics,  576 
Mytilotoxin,  115 
Myxedema,  341 

NAILS,  417 
Nasal  duct,  597 

reflex,  480 
Nates,  501 
Near-point,  565,  569 
Near-sightedness,  571 
Neck,  motor  area  of,  511 
Neck-sweetbread,  346 
Negative  accommodation,  565 

blood-pressure,  323 

variation  current,  458 
Nephrectomy,  effects  of,  427 
Nerve-cells,  69 

development  of,  73 

of  spinal  cord,  474 
Nerve-center,  cord  as,  478,  480 
Nerve-centers  of  medulla,  486 
Nerve-fibers,  63 

depressor,  488 

development  of,  73 
Nerve-impulses,  465 
Nerves,  461-464 

cardiac,  318,  525 

cranial,  513 

olfactory,  531 
functions  of,  533 

spinal,  475 

functions  of,  482 

trophic,  519 

vasoconstrictor,  488 

vasodilator,  488 

vasomotor,  462,  488 
Nervi  erigentes,  631 

nervorum,  64 
Nervous  functions,  460 

system,  468 

tissue,  63 

chemistry  of,  74 
proteids  of,  75 
Neu raxes,  69 
Neuraxon,  71 
Nt-urilemma,  64 
Neuroblasts,  73 
Neuroglia,  72 
Neurokeratin,  117 
Neurolemma,  64 
Neuron,  71,  73 


INDEX. 


Neuroplasm,  64 

Nipple,  144 

Nissl's  granules,  69 

Nitric-oxid  hemoglobin,  281 

Nitrogen  in  body,  86 

Nitrogenous  foods,  126 

Nodes  of  Ranvier,  64 

Noises,  620 

Normal  salt  solution,  81 

Nose,  353 

Nuclear  matrix^  25 

membrane,  25 
Nucleic  acid,  111 
Nuclein,  25 
Nucleins,  111 
Nucleo-albumins,  112 
Nucleohiston,  291 
Nucleolus,  25,  637 

true,  25 
Nucleoproteids,  111,  112,  294 

in  urine,  438 

poisonous  property  of,  113 
Nucleus,  25 

fecundation,  657 
Nutrient  artery,  44 

foramen,  44 
Nutritive  functions,  167 

OBLIQUE  muscles,  558 
Obliquus  externus,  371 

internus,  371 
Occipital  lobe,  498 
Ocular  muscles,  556 

functions  of,  559 
Odontoblasts,  50 
Odontoclasts,  55 
OEstrus,  647 
Oils  as  food,  125 

gastric  absorption  of,  255 
Old  sight,  572 
Olein,  99 
Olfactory  bulb,  531 

cells,  531 

glomeruli,  532 

membrane,  530 

nerve-fibers,  532 

nerves,  531 

function  of,  533 

sulcus,  533 

tract,  533 
Olivary  body,  485 
Oliver's  hemacytometer,  273 

hemoglobinometer,  277 
Omohyoid  muscle,  355 
Oncometer,  338 
Opaque  bodies,  589 
Ophthalmic  nerve,  516 
Ophthalmoscope,  580 
Optic  angle,  563 

constants,  561 

disk,  549 

thalami,  501 


INDEX. 


679 


Optogram,  582 

Ora  serrata,  547 

Orbits,  541 

Organ,  definition  of,  17,  18 

of  Corti,  613,  614 

of  Golgi,  69 

Organic,  definition  of,  18 
Organs  of  body,  relations  between,  460 
Os  orbiculare,  603 
Osmometer,  104 
Osmosis,  81,  104 
Ossein,  115 
Ossicles  of  ear,  602 
ligaments  of,  604 
muscles  of,  604 
Ossification,  40,  45 

center  of,  46 

endochondral,  46 

intracartilaginous,  46 

intramembranous,  46 

superiosteal,  45 
Osteoblasts,  43 
Osteoclasts,  44,  49 
Osteogenic  fibers,  46 
Ostiurn  abdominale,  640 
Otic  ganglion,  520 
Otoconia,  610 
Otoliths,  "610 
Ova,  638 

holoblastic,  657 

in  Fallopian  tubes,  644 

in  Graafian  follicles,  635 

liberation,  642 

maturation  of,  651 

meroblastic,  657 

nucleolus  of,  637 

nucleus  of,  637,  638 

primitive,  635,  637 
Ovarian  ligament,  631 

pregnancy,  654 
Ovary,  631  * 

cortex  of,  633 

medulla  of,  633 
Overtones,  harmonic,  622 
Ovula  Nabothi,  642 
Ov  ulation,  642 

and   menstruation,   relation   between, 

648 
Oxygen  and  carbon  dioxid,  interchange 

of,  between  air  and  blood,  383 
between  blood  and  tissues,  386 
in  lungs,  382 

in  body,  86 

tension  of,  in  blood,  383 
Oxyhemoglobin,  276,  279 

spectrum  of,  285 
Oxyntic  cells,  193 
Oxyphils,  289 

PACINIAN  corpuscles,  65 
Pain,  sense  of,  530 
Palmitin,  99 


Pancreas,  229 

innervation  of,  238 

removal  of,  239 

secretion  of,  232 
internal,  239 

structure  of,  229 
Pancreatic  fistula,  233 

juice,  233 

emulsifying  powers  of,  237 
enzymes  of,  235 
milk-curdling  enzyme  of,  238 
secretion  of,  239 
Papain,  113 
Papillae,  circumvallate,  536 

conical,  537 

filiform,  537 

fungiform,  537 

lingual,  536 
Papillary  muscles,  316 

of  heart,  307 
Paraglobulin,  110 
Paralysis,  cerebral,  501 

of  motion,  464,  501 

of  sensation,  464 
Paranucleins,  112 
Para  plasm,  24 
Parathyroid,  339,  345 
Parietal  cells,  193 

lobe,  498 

Parieto-occipital  fissure,  497 
Paroophoron,  638 
Parotid  gland,  anatomy  of,  172 
nervous  supply  of,  176 
secretion  of,  180 
Parotitis,  173 
Parovarium,  638 
Pars  ciliaris  retinae,  547,  554 

optica  retinse,  547 

minute  structure  of,  550 
Parturition,  center  for,  482 
Pasteurization,  144 
Patellar  reflex,  480 
Patheticus,  514 
Pavilion,  640 

Pavy's  glycogenic  theory,  258 
Pecquet's  cistern,  331 
Pectoralis  major  and  minor,  370 
Peduncular  fibers,  506 
Pekelharing's  blood-coagulation   theory, 

297 
Penis,  630 

erection  of,  651 
Pepsin  in  gastric  juice,  198 
Pepsin-hydrochloric  acid,  198 
Pepsinogen,  198 
Peptones,  gastric  absorption  of,  255 

gelatin,  200 

poisonous  property  of,  113 
Peptonuria,  438 
Percussion-wave,  328 
Pericardium,  305 
Pericementum,  54 


080 


INDEX. 


Perichondrium,  41 

Peri  lymph- waves,  conversion  of  sound- 
waves into,  616 
Perimysium,  58 
Perineurium,  64 
Period  of  vibration,  620 
Periosteum,  43 

dental,  55 

Peripheral  resistance,  319 
Peristalsis,  457 

of  esophagus,  189 
Perivitelline  space,  637 
Perspiration,  414 
Perspiratory  glands,  413 
Pettenkofer's  test,  248 
Peyer's  patches,  226 
Pfliiger,  primary  egg-tubes  of,  635 
Phagocytosis,  290 
Phakoscope,  Helmholtz,  568 
Phalanges,  Deiters',  615 
Phloridzin,  260 
Phlorizin-diabetes,  260 
Phonation,  393 

laryngoscopic  image  during,  391 
Phosphates,  earthy,  86 

in  body,  82.     See  also  Calcium,  Mag- 
nesium, etc. 

Phospho-glucoproteids,  112 
Phosphorized  fat,  101 
Phrenic  nerves,  388 
Physiologic  chemistry,  76 

ingredients,  76 

salt  solution,  81 
Physiology,  animal,  20 

branches  of,  19 

definition  of,  17 

human,  defined,  20 

vegetable,  19 
Phytalbumose,  153 
Pialyn,  236 

Piano  theory  of  hearing,  618 
Pigeon-breast,  353 
Pigmentary  layers  of  retina,  553 
Pigments,  mixing  of,  590 

respiratory,  276 

retinal,  566 
Pineal  gland,  351 
Pinna,  598 

Piotrowski's  reaction,  103 
Pitch,  392,  621,  623 
Pituitary  body,  351 
Placenta,  660 

circulation  of,  661 
Plantar  reflex,  479 
Plaques,  291 
Plasma,  108 

blood,  291.     See  also  Blood-plawia. 

muscle-,  62 

salted,  295 
Plasma-cells,  35 
Plethysmograph,  329 
Pleura,  362,  365 


|  Plenral  cavity,  365 
Plexus,  intra-epithelial,  544 

subepithelial,  544 
Pneumogastric  nerve,  523 
Pohl's  commutator,  447 
Poikil'othermal  animals,  407' 
Polarimeter,  88 
Polariscope,  88 
Polarization,  88,  444 
Polarizing  current,  466 
Poles  of  cells,  70 
Polysaccharids,  95 
Pomum  Adami,  354 
Pons  Varolii,  488 
Portal  canals,  239 

vein,  241 
Portio  dura  of  facial,  521 

mollis  of  facial,  521 
Porus  opticus,  541 ,  549 

positive  accommodation,  565 
Post-dicrotic  wave,  328 
Posterior  chamber  of  eye,  554 

gray  commissure,  471 

horn,  cells  of,  474 

intermediate  furrow,  471 

median  fissure,  471 
Posterolateral  column,  474 

fissure,  471 

Posteromedian  column,  473 
Potassium  carbonate,  83 

chlorid,  84 

phosphate,  82 

sulphate,  63 

Pre-antral  constriction,  200 
Precipitins,  301 

in  identifying  blood-stains,  301 
Predicrotic  wave,  328 
Pregnancy,  abdominal,  654 

ampullar,  655 

anomalous  varieties,  656 

cornual,  656 

corpus  luteum  of,  651 

ectopic,  655 

extra-uterine,  655 

infundibular,  656 

interstitial,  655 

ovarian,  654 

peritoneal,  654 
Presbyopia,  572 
Pressure  sense,  529 
Primary  pulse  wave,  328 
Primitive  sheath,  64 
Processus  ad  medullam,  491 

cochleariformis,  604 

e  cerebello  ad  testes,  491 
Projection-fibers,  505,  506 
Pronucleus,  female,  651 

male,  657 
Protagon,  75 
Proteids,  102 

absorption  of,  260 

action  of  gastric  juice  on,  199 


INDEX. 


681 


Proteids,  action  of,  on  polarized  light, 
103 

as  food,  125 

classification  of,  107 

coagulated,  108,  113 

color-reactions  of,  103 

crystallization  of,  104 

glycogen  formation  from,  257 

in  urine,  438 

non-diffusibility  of,  104 

of  liver,  240 

poisonous,  113 

precipitation  of,  106 

vegetable,  155 
Protein,  110 
Proteoses,  poisonous  property  of,  113 

primary,  199 

secondary,  199 
Prothrombin,  292,  294 
Protoplasm,  24 
Protoplasmic  process,  72 
Proto-proteose,  199 
Pseudonucleins,  112 
Pseudonucleoli,  25 
Pseudopodia,  24 
Ptomain,  114 
Ptosis,  514 
Ptyalin,  97,  182 
Ptyalinogen,  180 
Pulmonary  alveoli,  363 

artery,  364 

capillaries,  364 

circulation,  311 

nerves,  525 

valve,  308 

veins,  364 
Pulsation,  311 

maximal,  322 
Pulse,  318,  326 

dicrotie,  329 

record  of,  327 

volume,  314,  329 

waves,  328 
Pulse-trace,  327 
Puncta  lacrimalia,  597 
Punctum  pioximum,  565,  569 

remotum,  570 
Puncture-diabetes,  259 
Pupil,  545 

contraction    of,    during    accommoda- 
tion, 570 

membrane  of,  546 
Purin,  435 

bases  and  uric  acid,  434 
Purin-bodies  in  alcoholic  beverages,  157 
Purkinje's  cells,  491 

figures,  577 

Purkinje-Sanson  images,  567 
Purple,  visual,  556,  581 
Pyloric  glands,  193 

muscle,  192 

orifice,  191 


Pylorus,  movements  of,  201 
Pyramidal  tracts,  473 
Pyramids  of  brain,  485 

QUADRATUS  lumborum,  371 
Quality  of  sound,  621,  623 

RACEMOSE  glands,  compound,  174 
Kami  communicantes,  488 
Ranvier's  nodes,  64 
Rations,  30 
Reason,  508 

Receptaculum  chyli,  331 
Recollection,  508 
Rectus  abdominalis,  372 

muscles,  557 

functions  of,  559 
Recurrent  sensibility,  483 
Red  corpuscles,  270 

chemical  composition  of,  275 
color  of,  274 
destruction  of,  287 
development  of,  286 
function  of,  288 
number  of,  271 
spleen  and,  338 
structure  of,  275 
Reflex  action,  478-481 

arc,  479 

centers  of  medulla,  486 

deep,  480- 

in  man,  479  •* 

superficial,  479 

time,  479 
Regio  olfactoria,  530 

respiratoria,  530 

vestibularis,  530 

Reichert's  water  calorimeter,  410 
ReiFs  island,  497,  498,  500 
Reissner's  membrane,  609,  613 
Relative  humidity,  376 
Remak's  fibers,  64  • 

Remembrance,  508 
Renal  arteries,  424,  425 
Rennin,  112 

in  gastric  juice,  198 
Reproduction,  624 

organs  of,  624.     See  also  Genital  Or- 
gans. 

Residual  air,  375 
Resonance,  391 
Resonators,  623 
Respiration,  352 

apparatus  of,  353 

at  birth,  663 

blood-changes  from,  381 

chemistry  of,  376 

Cheyne-Stokes,  387 

efferent  nerves,  388 

female  type,  375 

frequency  of,  375 

innervation  of,  386-388 


682 


L\DEX. 


Respiration,  internal,  386 

t&rvngOBOOpic  image  during,  391 

male  type,  375 

movements  of,  372 
rhythm  of%386 

muscles  of,  367 

of  skin,  419 

Respiration-calorimeter,  164 
Respiratory  center,  386,  481 

pigment,  276 

quotient,  377 
Restiform  body,  485 
Eete  mueosum,  413 

test  is,  627 

Retieular  lamina,  615 
Reiieulin,  116 
Retieulum,  24 
Retiform  tissue,  37 
Retina,  547,  576 

central  artery  of,  541,  549 

chemistry  of,  555 

circulation  in,  579 

epithelium  of,  552 

fatigue  of,  594 

layers  of,  550-553 

pars  optica  of,  minute  structure  of,  550 

pigmentary  layer  of,  553 

n-ilexof,  580  * 
Retinal  image,  562,  563 
Retzius'  fiber-cells,  610 
Reunions,  canalis,  611 
Reverse  air,  374 
Rheoseope,  physiologic,  458 
Rhodopsin,  556,  581 
Khomhoidei,  370 
Rhythmieality,  457 
Ribs,  365 
Ricin,  113 

Rigor  mortis,  62,  111,  456 
Ring  muscle  of  Miiller,  544,  546 
Rima  glottidis,  359 
Rivinus'  ducts,  174 
Rod-bipolars,  551 
Rod-elements,  552 
Rod -fiber,  Rod-granules,  552 
R..ds  :>.vj 

Rolandic  area,  509,  510 
Rolando's  lissure,  497 

funieulus,  485,  486 

Rontgen  rays  in  examination  of  stom- 
ach, 201 

Root-fiber,  anterior,  73 
Routs  of  spinal  nerves,  475 
Rope,  the,  581 
Rosenmiiller's  organ,  638 
Rotatory  power,  specific,  91 
Riiira'  01  stomai-h,  192 
Rumination,  486 
Rut,  647 

SACCHARTMETER,  89 
Saccharoses,  93 


Sacrule,  610,  623 
Sacculus  laryngis,  359 
Sacrolumbalis,  370 
Saliva,  alkalinity  of,  181 

amylolytic  action  of,  183 

celte  of,  changes  in,  180 

chemical  action  of,  182 
examination  of,  187 

composition  of,  180 

corpuscles  of,  181 

effect  of  alcohol  on  secretion  of,  159 
of  nerve-stimulation  on,  176 

mixed,  181 

with  gastric  juice,  195 

offices  of,  182-185 

properties  of,  180 

secretion  of,  179 

taste  and,  185 
Salivary  calculi,  182 

glands,  anatomy  of,  172 

secretory  nerves  of,  176 
Salted  plasma,  295 
Salts  as  food,  123 

excretion  of,  426 

in  body,  80 

Santorini's  cartilages,  354 
Sapokrinin,  239 
Saponification,  100 
Sarcolemma,  56 
Sarcomeres,  59 
Sarcoplasm,  57 
Sarcostyles,  57 

Sarcous  element  of  muscle,  59 
Sartoli's  columns,  625 
Scala  media,  609 

tyrnpani,  608 

vestibuli,  609 
Scaleni,  367 

Schemer's  experiment,  569 
Schlatter's  case  of  stomach  extirpation, 

212 
Schmidt's  theory  of  blood-coagulation, 

297 

Schmiedeberg's  ferratin,  240 
Schoen's  theory  of  accommodation,  569 
Schulze's  tests  for  glycogen,  98 
Schwann's  nucleated*  sheath,  64 

white  substance,  64 
Sclerocorneal  junction,  546 
Sclerotic  tunic  of  eye,  541 
Sebaceous  glands,  416 
Sebum,  416 
Second  sound,  316 
Secretin,  239 
Segmentation,  657 
Semen,  629 

ejaculation  of,  652 
Semicircular  canals,  607,  623 

impressions  from,  493 

membranous,  612 

positions  of,  494 

result  of  injury  to,  493 


INDEX. 


683 


Semilunar  valves,  307,  308 
Seminiferous  tubules,  625 
Senile  atrophy,  84 
Sensation,  paralysis  of,  464 
Senses,  527 

special,  trigeminus  and,  518 
Sensibility,  general,  527 

recurrent,  483 

tactile,  527 

Sensorimotor  area,  509,  510 
Sensory  area,  509,  512 

fibers,  recurrent,  483 
Septum,  auricular,  308 

ventricular,  308 
Serous  glands,  174 

membranes,  333 
Serrati  muscles,  370,  371 
Serum,  108 

bactericidal  property  of,  300 

blood,  294 

globulicidal  action  of,  300 
Serum-albumin,  108 
Serum-globulin,  110 
Sharpey's  perforating  fibers,  43 
Shock,  reflex  action  and,  480 
Shrapnell's  membrane,  602 
Sight,  563 

long,  572 

old,  572 

sense  of,  541 
Silicon,  86 

Singing,  resonance  chamber  in,  395-406 
Size,  appreciation  of,  583 
Skatol,  266 

Skatoxyl  in  urine,  439 
Skein,  29 
Skeletal  muscle,  61 

Skin,  413' 

care  of,  419 

excretion  of,  418 

functions  of,  418 

nerves  of,  in  respiration,  388 

protection  furnished  by,  418 

respiration  by,  419 

sensation  in,  418 

temperature  and,  419 
Smell,  sense  of,  530 

acuteness  of,  535 
Snake-poison,  113,  114 
Soap,  100 

emulsification  and,  237 

theory  of  fat-absorption,  263 
Sodium  carbonate,  83 

chlorid,  80 
in  osmosis,  81 

glycocholate,  247 

phosphate,  82 

sulphate,  83 

taurocholate,  247 
Solar  spectrum,  283,  587 
Solitary  glands,  226 


Soluble  starch,  96 

Solution  theories  of  fat-absorption,  263 
Somatopleure,  659 
Sum  men-ing's  foramen,  548 
yellow  spot,  548,  553J  577 
Sonometer,  622 
Sonorous  bodies,  616 
Sound  conduction  through  skull  bones, 

618 

definition  of,  616 
Sounds,  620 
Sound-waves,  616 
Spectroscope,  283 
Spectrum,  283,  587 
Speculum,  aural,  600 
Speech,  389,  393 
Speech-center,  511 
Spcnnatoblasts,  625 
Spermatogenesis,  625 
Spermatoxin,  301 
Spermatozoa,  625 
passage  of,  652 

Sphenopalatine  ganglion,  520 
Sphincter  antri  pylorici,  194 
internal,  227 
pupillae,  545 
pyloricus,  192 

movements  of,  201 
vesicae,  429 
Sphygmograph,  327 
Sphygmometer,  322 
Spider-cells,  73 
Spinal  accessory  nerve,  525 
columns,  471 
cord,  468 

as  nerve-center,  478,  480 
conduction-paths  in,  477 
enlargements  of,  468 
fissures  in,  471 
functions  of,  477 
gray  matter  of,  473 
minute  structure  of,  472 
nerve- cells  of,  474 
reflex  action  of,  478 
section  of,  471 
special  centers  of,  481 
tracts  of,  473 
white  substance  of,  472 
ganglia,  476 

functions  of,  483 
nerves,  475 

functions  of,  482 
in  respiration,  388 
Spiral  canal  of  ear,  608 
Spirem,  29 
Spirits  as  food,  157 
Splanchnopleure,  659 
Spleen,  335 

contraction  and  expansion  of,  338 
corpuscles  and,  338,  339 
during  digestion,  337 
enzymes  and,  339 


684 


INDEX. 


Spleen,  uric  acid  and,  339 
Splenic  arterv,  337 

cells,  44 

pulp,  336 
Spongework,  24 
Spongioblasts  of  retinal  molecular  layer, 

551 

Spongioplasm,  24 
Spreading  of  reflexes.  478 
Stains,  blood-,  precipitins  in  identifying, 

301 

Staircase  curve,  455 
Stapedius,  604 
Stapes,  603 
Starch,  95-97 
Starch-grains,  95 
Starch-paste,  96 
Steapsin,  236 
Stearin,  99 

Stellar  phosphates,  441 
Stellate  reticulum,  55 
Stenson's  duct,  173 
Stercobilin,  247,  266 
Stereoscope,  583 
Sterilization  of  milk,  144 
Sternohybid  muscle,  355 
Sternomastoid,  370 
Sternothyroid  muscle,  355 
Stilling's  canal,  554 
Stimulation,  443,  444 

previous,  effect  on  muscle-curve,  455 
Stimuli,  442,  443 

protoplasmic,  24 

summation  of,  453 
Stomach,  191 

absorption  in,  254 
of  alcohol  from,  161 

changes  in,  in  digestion,  204 

digestion,  191,  208 

excretory  function  of,  209 

movements  of,  200 
effect  on  food,  205 

progressive  atrophy  of,  219 

removal  of.  211,  214 

Rontgen  rays  in  examination  of,  201 

ruga?  of,  192 

self-digestion  of,  208 
Stomata,  333 
Strabismus,  external,  514 
Straight  tubes,  627 
Stratum  granulosum,  634 
Stria?,  56 

Striated  muscle,  56 
Stroma,  545,  633 
Stromuhr,  323 
Stylohyoid  muscle,  355 
Subclavius,  371 
Sul>epithelial  plexus,  544 
Sublingual  gland,  174 
iK-rve-supply  of,  177 
secretion  of,  181 
Sublobular  vein,  241 


Submaxillary  ganglion,  521 

gland,  173 

nerve-supply  of,  177 
secretion  of,  180 
Subsidiary  centers,  386 
Substantia  cinerea  gelatinosa,  472 

gelatinosa  centralis,  472 

lateralis,  472 
Succus  entericus,  228 
Sucking  center,  486 
Sudorific  center,  481 
Sudoriparous  glands,  413 
Sugar,  composition  of,  124 
Sulci,  496 
Sulphates,  83 

Sulphuretted  hydrogen,  86 
Superior  intercostal  vein,  364 

maxillary  nerve,  516 

oblique,  558 

rectus,  557 

Supplemental  air,  374 
Suprarenal  capsules,  347-349 
Suspensory  ligament,  555 
Sustentacular  cells,  336,  537,  625 
Swallowing,  189,  190 
Sweat,  414 
Sweat-gland,  413 
Sweetbread,  346 
Sylvius'  fissure,  496 
Sympathetic  nerve,  effect  of  stimulation 

of,  177 

Synaptase,  72 
Syntonin,  109 
System,  definition  of,  19 
Systemic  circulation,  311 
Systole,  312 
Systolic  sound,  316 

TAIL  fold  of  blastoderm,  658 
Tapetum  nigrum,  553 
Tartar,  182 
Taste,  facial  paralysis  and,  522 

saliva  and,  185 

sense  of,  535 

conditions  of,  540 
Taste-buds,  537 
Taurin,  247 
Tea,  156 
Tears,  597 
Teeth,  50,  55,  171 

development  of,  54 

in  mastication,  171 
Tegmen,  592 
Tegmentum,  499 

Telephone  theory  of  hearing,  619 
Temperature,  406,  407 

effect  on  muscle-curve,  455 

regulation  of,  413 

sense,  529 

skin  as  regulator,  419 
Temporosphenoidal  lobe,  498 
Tendo  A  chillis  reflex,  480 


INDEX. 


685 


Tendon  reflexes,  480 
Tendon-cells,  38 
Tenon's  capsule,  541 
Tension  of  dissociation,  383 
Tensor  tympani,  604 
Testes,  601,  625 
Test-meals,  210 
Tetanin,  115 
Tetanus,  454 

secondary,  458 
Theca  folliculi,  634 
Them,  156 

Thiry-Vella  fistula,  228 
Thoma-Zeiss  hemacytometer,  272 
Thoracic  cavity,  365 

duct,  331 
Thorax,  365 

aspiration  of,  330 

respiratory  muscles  of,  367 
Throat-sweetbread,  346 
Thrombin,  292 
Thrombosin,  297 
Thymus,  346 
Thyreo-antitoxin,  340 
Thyreoproteid,  340 
Thyro-arytenoideus  muscle,  357 
Thyro-ep'iglottideus  muscles,  357 
Thyrohyoid  muscle,  355 
Thyroid,  339 

arteries,  341 

cartilage,  354 

colloid  liquid  of,  340 

extract,  342 

innervation  of,  341 

internal  secretion  of,  342 

removal  of,  341 

treatment,  343 

venous  plexus,  361 

vesicles,  340 
Thyroidectomy,  341 
Thyro-iodin,  340 
Tidal  air,  374 

wave,  328 

Timbre,  393,  621,  623 
Time-markers,  450 
Tissues,  elementary,  30 

epithelial,  30.     See  also  Epithelium. 
Tone-color,  621,  623 
Tones,  621,  622 
Tongue,  186 

mucous  membrane  of,  536 

nerves  of,  536 
Ton  us,  muscular,  456,  481 
Touch,  sense  of,  527 
Toxalbumins,  114 
Trachea,  361 
Tracheal  glands,  361 
Trachealis  muscle,  361 
Transparent  bodies,  589 
Transversalis,  372 
Transverse  band,  194 

fibers,  506 


Trapezius,  369 
Travel  ration,  132 
Trial-meals,  210 
Triangularis  sterni,  371 
Tri  cuspid  valve,  307 
Trifacial  nerve,  515 
Trigeminus,  515 

anastomosis  of,  518 

ganglia  of,  520 

nerve,  388 

special  senses  and,  518 

trophic  influence  of,  519 
Trigonum  olfactorium,  533 
Trochlearis,  514 
Trommels  test  for  dextrose,  87 
Trophic  centers,  482 
Tropical  diet,  135 
Trunk,  motor  area  of,  511 
Trypsin,  235 
Tryptic  digestion,  236 
Tscherningfs  theorv  of  accommodation, 

568 

Tuberculosis  from  eating  raw  meat,  150 
Tubular  glands,  compound,  174 
Tubuli  lactiferi,  144 

uriniferi,  422 
Tunica  advehtitia,  310 

albuginea,  633 

externa,  634 

interna,  634 

intima,  308 

media,  308 

propria,  336 

Ruyschiana,  544 

vaginalis  oculi,  541 
Tiirck's  fasciculus,  473 
Twitch,  451 

Tympanic  cavity,  600,  602 
Tympanum,  600 

muscle  of,  604 

Typhoid  fever  from  drinking-water,  122 
Typhotoxin,  115 
Tyrotoxicon,  115 

UMBO,  602 

United  States'  ration,  133,  134 
Unpolarizable  electrodes,  447 
Urea,  432 

excretion  of,  427 
Ureters,  428 
Urethra,  430 
Uric  acid,  433 

excretion  of,  427 

influence  of  alcohol  on,  161 

purin  bases  and,  434 

spleen  as  producer  of,  339 

test  for,  434 
Urinary  apparatus,  421 
Urination,  430 
Urine,  431 

after  stomach  removal,  214 
Albumin  in,  438 


686 


INDEX. 


Urine,  albumoses  in,  438 

alloxuric  substances  in,  437 

aromatic  substances  in,  439 

carbonates  in,  441 

chlorids  in,  440 

color  of,  431 

composition  of,  426,  432 

creatinin  in,  438 

dextrose  in,  439 

formation  of,  426 

hippuric  acid  in,  437 

inorganic  constituents  of,  440 

lactose  in,  439 

peptone  in.  438 

phosphates  in,  440 

proteids  in,  438 

specific  gravity  of,  432 

sulphates  in,  441 

sulphur  in,  441 

urea  in,  432 

uric  acid  in,  433 

xanthin  bases  in,  437 
Urobilin,  247,  431 
Urobilinogen,  431 
Urochrome,  431 
Uroerythrin,  431 
Uterine  glands,  641 
Uterus,  640 
Utricle,  610,  623 
Utriculus,  610,  623 

VAGI  nerves,  388 
Vagus,  523 
Valvula  Heisteri,  244 
Valvuke  conniventes,  222 
Vas  aberrans,  627 

deferens,  628 
Vasa  recta,  627 

vasorum,  310 
Vascular  glands,  334 
Vasomotor  center,  481 

of  medulla,  487 
Vater's  corpuscles,  65 
Vegetable  proteids,  absorption  of,  261 
Vegetables  as  food,  155 
Vegetarianism,  128 
Veins,  310 

bronchial,  364 

circulation  in,  329 

compression  of,  329 

pulmonary,  364 

rate  of  flow  in,  325 
Vena  azygos  major,  364 
Vena?  vorticose,  544 
Ventilation,  378 

positive,  387,  388 
Ventricles,  306,  307 

blood  expelled  from,  314 

work  done  by,  315 
Ventricular  septum,  308 

systole,  312 
Vernix  caseosa,  416 


Vertebra,  365 
Vertebral  column,  365 
Verumontanum,  631 
Vesicospinal  center,  482 
Vesicula  seminalis,  629 
Vestibular  nerve,  616 
Vestibule  of  ear,  607 
Vibration,  period  of,  620 
Vibration-frequency,  620,  623 
Villi  cells,  224 

intestinal,  222 

of  chorion,  660 
Viperin,  114 
Vis  a  tergo,  329 
Vision,  binocular,  583 

physiology  of,  560 
Visual  angle,  563 

apparatus,  defects  of,  570 

area,  512 

judgment,  595 

purple,  566,  581 
Vital  capacity,  375 

heat,  406 

losing  of,  410 
sources  of,  409 

phenomena,  17 
Vitellin,  113 
Vitelline  circulation,  661 
Vitellus,  638 
Vitreous  body,  554,  556 

humor,  554,  556 
Vocal  cords,  358,  360 

in  change  of  register,  400 
in  singing,  398 
Voice,  389,  392 
Volume-pulse,  329 
Voluntary  muscle,  56 
Vomiting,  205 

after  stomach  removal,  214 

center,  486 

Von  Fleisch's  hemometer,  278 
Vowels,  394 

WALKING,  cord  and,  480 
Wallerian  degeneration,  464 

method    of    determining     course    of 

nerve-fibers,  473 
Warm-blooded  animals,  406,  407 
Water,  121 

absorption  of,  in  stomach,  254 

excretion  of,  80,  426 

in  body,  78 

intestinal  absorption  of,  256,  265 

quantity  of,  in  food,  79 
Weidel's  reaction,  434 
Welcker's  method  of  blood  estimation. 

269 

Wharton's  duct,  173 
Wheat-flour,  154 
Whey,  112,  143 
Whey-proteid,  112 
Whirling  machine,  590. 


INDEX. 


687 


Whiskey  as  food,  157 
White  corpuscles,  288.     See  also  Leuko- 
cytes. 

fibrous  tissue,  38 

matter  of  cerebrum,  505 

nervous  matter,  63 

of  egg,  149 

of  eye,  541 

substance,  472 
Whole-wheat-flour,  154 
Windpipe,  361 
Wines,  157 
Wisdom-teeth,  55 
Wrisberg's  cartilages,  354 

XANTHIN  bases,  437 
Xanthoproteic  reaction,  103 


YELLOW  spot  of  Sommerring,  548,  553, 

577 

Yolk  of  egg,  149 
Yolk-sac,  660 

walls  of,  659 
Young-Helmholtz  color  theory,  591 

Birch  modification  of,  592 

ZALESKI'S  hepatin,  240 
Zinn's  tendon,  557 
Zollner's  lines,  596 
Zona  fasciculata,  348 

pellucida,  637,  638 

reticularis,  348 

vasculosa,  633 
Zymogen,  119 
Zymolysis,  118 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
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WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
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OVERDUE. 


JBEO. 

MAY   2  1933 

APR   19  1934 
JAN    2  1934 

SFP  201935 


logy  Lfeary- 


EC  16   1937 


ffrrr  3 1964 


„       to  Recall 
Immediately 


LD  21-50m-l,'3 


BIOLOSY 
LIBRARY 

UNIVERSITY  OF  CALIFORNIA  LIBRARY 


